Authors : E. Alves Ion Beam Laboratory, Instituto Tecnológico e Nuclear EN. 10, 2686-953 Sacavém Portugal
Resume : During the last decades wide band-gap semiconductors became one of the most studied type of materials which led to a new generation of optoelectronic devices operating in the visible region of the electromagnetic spectrum. Although the entire visible region could be covered playing with the concentration of indium in the ternary In1-xGaxN compound there are a great interest in using rare-earth (RE) doped GaN and ZnO to produce devices emitting in the UV-visible region. Rare-earth doping of nitrides opens new possibilities to built new all-nitride electroluminescent devices. In fact the sharp emissions of the intra 4f transitions of the RE ions in the visible (red (Eu, Pr), green (Er) and blue (Tm)) are independent of temperature and almost independent of the host. In addition Er allows the extension of the operation range to the infrared region of the electromagnetic spectrum. Despite the promising results obtained with MBE, ion implantation offers the possibility to control the doping process including lateral patterning. In this contribution we present recent developments on rare earth (RE) implanted III-nitrides and ZnO wide bandgap semiconductors. We discuss the implantation damage formation and annealing processes and show the possibility to achieve intense emissions. This is a fundamental issue if ion implantation happens to become a processing technique in this area.

Authors : S. Tafon Penn, Z. Fleischman, V. Dierolf
Resume : GaN is a very promising semiconductor host for rare-earth (RE) based electrically-pumped light emitters. Recently stimulated emission in Eu-doped GaN has been reported under optical excitation rekindling the hope that an electrically-pumped rare-earth-doped semiconductor laser can be realized. In these laser experiments performed under pulsed UV excitation that different types of Eu ions are contributing in a complicated way emphasizing the need to understand the excitation mechanism for different RE-incorporation sites. In our work, we study the Eu:GaN material system using site selective cathodoluminescence under intense E-beam excitation and combined excitation emission spectroscopy. We address the following questions: • Which incorporation sites can be excited through hot electrons and electron-hole pairs most efficiently? • What limits the overall excitation efficiency? We find that defect-trap related sites exhibit the most efficient excitation by energetic electrons while most of the RE ions on a substitutional site (“majority site) cannot be excited at all. To explain this behavior, we propose that in all cases the excitation involves a trap that mediates the energy transfer to the RE ion. The proximity of the RE ion to such traps will determine the transfer rate and in combination with the intrinsic trap lifetime the excitation efficiency of the RE ion/defect trap pair. The total number of suitable pairs limits the overall emission efficiency.

Authors : F. Gloux1, P. Ruterana1, K. Lorenz2 and E. Alves2 1SIFCOM, UMR 6176, CNRS-ENSICAEN, 14050 Caen, France 2Instituto Tecnológico e Nuclear, EN10, 2686-953 Sacavém, Portugal
Resume : Rare earth (RE) doped GaN has been the subject of research over the last decade due to promising applications in optoelectronics and photonics. Ion implantation has many advantages for device production: control of the doped area, formation of highly resistive region, easy lateral and multiple RE integration. However, it causes a large undesirable structural damage in the GaN, which requires high temperature annealing for the RE optimal activation. Implanting GaN through an ultrathin epitaxial AlN cap has been reported as an efficient way to reduce the amount of induced damage. Using such a cap allows to implant REs with fluences one order of magnitude higher, i.e. about 3×1016RE/cm2, at 300keV and RT, before a highly disordered layer with nanocrystalline structure is formed. In this work, we present a detailed structural study of the damage build-up mechanisms in GaN versus the fluence when implantation is performed through the AlN cap at 300keV and RT, in comparison with the implantation in uncapped GaN. Investigation of the structure of AlN capped GaN layers implanted in the [0.5-3]×1016RE/cm2 range showed a damage build-up that proceeds first by nanocrystalline patches forming below the AlN cap. The high resistance of AlN to the damage formation is highlighted by the evolution of the damaged structure for higher fluences.

Authors : R. Ma?j, M. Dammak, S. Kammoun, M. Kammoun Laboratoire de Physique Appliqu? Groupe de Physique Th?ique, D?rtement de Physique, Facult?es Sciences de Sfax, 3018 Sfax, Tunisie.
Resume : Er3+ -doped GaN have spurred extensive interest because of their potential applications as electroluminescent devices in visible and infrared range used in optical communications and full colour displays. Generally, these optical properties are closely related to the local structure and dynamical behaviours of the Er3+ impurity in the GaN host. Since electronic paramagnetic resonance (EPR) is powerful tool to acquire useful information about electronic states and local structures of paramagnetic impurities in crystals, EPR experiments have been carried out on GaN:Er3+ systems [1]. The EPR-g factors ( g// and gT ) and hyperfine structure factors ( A// and AT ) have been measured previously. Until now, however, the experimental results have not been theoretically interpreted and local structures for the Er3+ center have not been obtained either. Since that information about the local structure of the Er3+ impurity in GaN may be helpful to understand optical properties of the materials, theoretical investigations of the g and A factors and the local structure for the Er3+ centers are of significance. In this work, we will undertake both crystal-field and EPR parameters analysis in order to investigate the lattice location of the impurity centers in the host material. [1] M.Palczewska, A.Wolos, M.Kaminska, I.Grzegory, M.Krulowski, T.Suski, S.Porowski Solid State communications 114(2000) 39-42

Authors : A. Ishizumi(a), J. Sawahata(b), K. Akimoto(b), and Y. Kanemitsu(c), (a)Graduate School of Materials Science, Nara Institute of Science and Technology, Ikoma, Nara 630-0192, Japan, (b)Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan, (c)Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
Resume : Recently, much attention has been paid to optical properties of Eu3+-doped GaN (GaN:Eu3+) crystals, because they are expected to be key materials for full-color light-emitting diode and laser diode applications by GaN-based materials. In this work, we have fabricated the GaN:Eu3+ epitaxial films and have studied their microscopic photoluminescence (PL) properties by a home-built confocal optical microscope. The GaN:Eu3+ epitaxial films were grown on the sapphire (0001) substrates by gas-source molecular beam epitaxy. The GaN:Eu3+ epitaxial films show the efficient PL due to intra-4f transitions of Eu3+ ions. The intensity and spectral shape of the dominant PL peak at about 622 nm depend strongly on the Eu3+ concentration, the excitation wavelength, and the monitored position. Under the lower energy excitation (3.06 eV) below the band-gap energy of GaN host crystals, bright spots are clearly observed in the spatial images of the Eu3+-related PL intensity for the 1 at.% Eu3+ samples, and are attributed to the Eu3+ ions around point defects of GaN host crystals [1]. By contrast, bright lines due to dislocations are clearly observed for the 3 at.% Eu3+ samples [1]. The intensity of Eu3+-related PL is strongly correlated with the spatial distribution of the point defects and the dislocations. The site-dependent Eu3+ luminescence in GaN:Eu3+ epitaxial films will be discussed. [1] A. Ishizumi, et at., Appl. Phys. Lett. 89, 191908 (2006).

Authors : L. Bodiou, A. Braud, M. Wojdak, J-L Doualan, R. Moncorgé, CIRIL-ENSICAEN, 6 Bvd Maréchal Juin, 14000 Caen, France K.Lorenz, E.Alves, Instituto Tecnologico e Nuclear, Estrada Nacional 10, PT-2685-953 Sacavém,Portugal J. H. Park, C. Munasinghe, A. J. Steckl, University of Cincinnati, OH 45221-0030 Cincinnati, USA B. Pipeleers, A. Vantomme, Instituut voor Kern-en Stralingsfysica, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium
Resume : Rare-earth (RE) doped gallium nitride (GaN) is being widely studied for its various applications in optoelectronics such as electroluminescent emitter or laser. Nevertheless mechanisms underlying the excitation of RE ions in this host as well as the quenching mechanisms impairing the luminescence of rare-earth ions are still unclear. Excitation mechanisms are studied in Eu implanted and Eu in-situ doped GaN by Molecular Beam epitaxy (MBE). Two predominant Eu centres are optically active in both types of samples under above-bandgap excitation. One of these centres is common to both types of Eu doped GaN. PL dynamics are presented as a function of temperature or excitation wavelength and reveal that excitation paths of both Eu centres are clearly different. The same differences in the PL dynamics are observed in implanted and MBE samples. Differences between Eu and Er doped samples will be discussed. RE PL quenching mechanisms in GaN are studied using a set of two colour experiments. In a first experiment, the sample is illuminated by two CW laser sources and in a second experiment by a pulsed laser and a CW laser. A strong quenching of the RE luminescence is observed and its dependence with the excitation density and wavelengths of both lasers is presented. Results are explained within the frame of a model describing the photo-ionization of the carriers trapped at RE related levels within the bandgap and/or with Auger effects between free carriers and excited RE ions.

Authors : Hua Chen†, Ying Chen†*, Chi Pui Li†, Hongzhou Zhang†, James S. Williams†, Yun Liu‡, Zongwen Liu#, and Simon P. Ringer# †Research School of Physical Sciences and Engineering, The Australian National University, Canberra, ACT 0200, Australia, ‡Research School of Chemistry, The Australian National University, Canberra, ACT 0200, Australia #The Australian Key Centre for Microscopy and Microanalysis, University of Sydney, NSW 2006, Australia
Resume : Rare-earth ion doped boron nitride nanotubes combine wide-band-gap semiconductors and rare-earth luminescence with significant potential applications in nanosized lighting, display devices, and nano surgery. A broad and tunable visible light emission, excited by electrons, from Eu doped BN nanotubes has been realized for the first time. The special broad light emission is due to the insertion of Eu2+ ions into nanotube walls via in-situ Eu doping during nanotube growth instead of a common post-synthesis doping process.

Authors : K. Lorenz1,2, E. Alves1,2, T. Monteiro3, M. Peres3, A.J. Neves3, M.R. Correia3 1 - Instituto Tecnologico e Nuclear, Estrada Nacional 10, 2686-953 Sacavem Portugal 2 - CFNUL, Av. Prof. Gama Pinto, 1649-003 Lisboa, Portugal 3 - Departamento de Fisica, Universidade de Aveiro, 3810-193 Aveiro, Portugal
Resume : Eu doped GaN has been extensively studied due to the sharp emission in the red spectral region interesting for applications in electroluminescent devices and lasers. The semiconductor band gap can be tuned when using the ternary alloy AlxGa(1-x)N with different Al/Ga ratios. This can change the excitation mechanisms of the rare earth ions and the efficiency of light emission processes can be optimized by choosing the appropriate AlxGa(1-x)N host. AlxGa(1-x)N films grown on sapphire substrates with AlN contents from 0 to 100 % were implanted with Eu ions. The implantation damage and the lattice site were studied by Rutherford backscattering and channelling spectrometry. Al-containing alloys are more resistant to implantation damage than GaN. The Eu ions are incorporated on lattice sites slightly displaced from the substitutional cation-site along defined directions. The displacement increases with increasing AlN fraction probably because of the decreasing lattice parameter leaving less free space to accommodate the large RE ion as well as defects. Experiments performed with different implantation geometries indicate that the displacement is due to the interaction with defects caused by the implantation. Raman measurements were performed to further characterize implantation damage and natural defects. Photoluminescence (PL) spectra after annealing at 1100 ºC show Eu related luminescence lines in the red spectral region for all samples. The PL intensity strongly depends on the AlN fraction and on the measuring temperature. PL measurements between 10 and 293 K show different temperature quenching for samples with different Al contents.

Authors : K. Makarova, M. Stachowicz, V. Glukhanyuk, A. Kozanecki Institute of Physics, PAS, Warsaw, Poland C. Ugolini, J. Y. Lin, and H. X. Jiang, Kansas State University, Manhattan, Kansas 66506 USA J. Zavada U.S. Army Research Office, Durham, NC27709, USA
Resume : We report on electron spin resonance (ESR) and the high resolution photoluminescence (PL) studies of highly Er-doped (2x10^20 – 2x10^21 cm-3) MOCVD grown GaN epilayers [1]. In ESR the axial Er3+ spectrum was observed with g(par.) = 2.861 and g(perp.) = 7.645 characteristic for substitutional Er ions at Ga sites (C3V symmetry). Angular dependence of the ESR did not reveal the existence of lower symmetry centers. The high resolution Fourier transform PL of Er3+ near 1.5 micrometer, site selective PL and PL excitation measurements show that in all samples only one Er center exists. The spectra reveal nonuniform broadening of the PL lines, which increases with increasing Er contents from 0.3 cm-1 for 2x10^20 cm-3 to 0.7 cm-1 for 2x10^21 cm-3. Measurements of the temperature dependent PL intensity show that temperature quenching of the PL for UV (333 nm) excitation is on the order of 20-30% [1], however, for resonant excitation to the 4I9/2 state the PL intensity between 4 K and 300 K is reduced by a factor of ~6. The estimated characteristic quenching energy between 200 and 300 K is ~15 meV which points to phonon related rather than electronic nature of the quenching process. The 1:1 correspondence of the PL intensity at room temperature to Er concentration suggest that co-operative processes in Er pairs do not influence the PL efficiency. [1] C. Ugolini et. al., Appl. Phys. Lett. 89, 151903 (2006).

Authors : K. Wang1, K. Lorenz2, P.R. Edwards1, I.M.Watson3, E. Alves2, K.P. O’Donnell1, R.W. Martin1 1Department of Physics, SUPA, Strathclyde University, 107 Rottenrow, Glasgow G4 0NG, UK 2 ITN, Estrada Nacional 10, 2686-953 Sacavém, Portugal 3Institute of Photonics, SUPA, Strathclyde University, 106 Rottenrow, Glasgow G4 0NW, UK
Resume : Photoluminescence (PL) and PL excitation spectroscopy have been used to investigate Eu implanted AlGaN alloys with AlN fraction ranging from 0 to 100 %. Significant spectral changes have been observed in the high resolution PL spectra as the AlGaN host changes from pure GaN to pure AlN. Firstly, the main Eu multiplets due to the 5D0—7F2 transition shift from 620.8nm for GaN:Eu towards lower energy (to 624.4nm) for AlN:Eu. Secondly, the spectral pattern of the transition changes dramatically. For GaN:Eu, the main Eu multiplet comprises of several luminescence peaks arising from two Eu sites. One of these sites can be excited by a broad excitation band (from 360nm to 420nm) below the GaN bandgap, but not the other. When the AlN fraction increases to 15%, the spectral pattern changes into a doublet, associated with only one of sites corresponding to the two in GaN:Eu. Further increasing in AlN fraction causes a greater red-shift of the doublet. PLE spectra demonstrate the AlGaN band edge and a broad excitation band below bandgap. Tuning the excitation source to these bands, the spectral patterns are exactly the same as that excited above AlGaN bandgap. Thus, the Eu luminescence from AlGaN:Eu is only from a single Eu site analogous to that excited by below-gap excitation of GaN:Eu. A strong influence of the AlN content on the emission intensity of AlGaN:Eu is also observed.

Authors : Andrew Steckl University of Cincinnati Cincinnati OH USA a.steckl@uc.edu
Resume : Recently, great progress has been achieved towards the long-term goal of rare-earth-based semiconductor lasers. Visible (red) stimulated emission has been reported (ref. 1) from Eu ions incorporated in GaN layers grown by molecular beam epitaxy on sapphire substrates. To our knowledge, this represents the first lasing from any RE-doped semiconductor. This was followed by Eu stimulated emission (ref. 2) in GaN grown on silicon substrates which carried nitride templates, producing the first visible lasing on Si. This paper reviews our current understanding of rare earth lasing sites in GaN, the relationship between materials growth, materials properties and resulting lasing performance. The prospects and challenges for electrically pumped injection GaN:RE lasers are discussed. The impact and potential benefits of RE emission for Si-based photonics is considered and a summary comparison with other approaches for obtaining lasing on Si is presented. Ref. 1: J. H. Park and A. J. Steckl, “Laser action in Eu-doped GaN thin film cavity at room temperature”, Appl. Phys. Lett., 85,). Ref. 2: J. H. Park and A. J. Steckl, “Visible Laser Action on Silicon Using Eu-doped GaN Thin Films”, J. Appl. Phys., 98,).

Authors : Marie-France Joubert Université de Lyon, Université Claude Bernard Lyon 1, CNRS, Laboratoire de Physico-Chimie des Materiaux Luminescents (LPCML),Domaine Scientifique de La Doua, 10 rue A.M. Ampere, 69622 Villeurbanne CEDEX, FRANCE
Resume : Emitting light devices may be based on rare-earth or transition metal ion doped materials as most of these ions have metastable electronic states located in all the spectral range from the IR up to the VUV. As soon as the required emitted photons have high energy, optical excitation of the active ion can lead to ionization of the impurity ions and delocalization of electrons. So, to control excitation and emission mechanisms in luminescent materials used for mercury-free fluorescent tubes, plasma display panels, scintillators, solid state lasers or integrated optics, it is necessary to study the quantum efficiency of the dopant ion photoionization process, the lifetime and mobility of photoexcited electrons as well as the location of its energy levels within the forbidden band gap. A microwave method was developed recently in the LPCML showing the possibility of using a microwave resonant cavity setup for the study of photoconductivity in doped insulators. This presentation will describe this technique which is based on the detection of the dielectric response of the crystal placed into a microwave resonator and irradiated by pulses of laser light. Experimental results were obtained for rare-earth-doped scintillators, laser crystals as well as doped dielectric powders. The processes responsible for the enhancement of the luminescence efficiency of rare earth doped Si-rich silica layers or nanostructures can be studied also by means of such microwave method.

Authors : E.S.Nikonyuk*, V.L.Shlyakhovyi*, M.O.Kovalets*, M.I.Kuchma*, Z.I.Zakharuk**, I.M.Yuriychuk** *National University of Water Management and Conservation, Rivne, Ukraine **Chernivtsi National University, Chernivtsi, Ukraine
Resume : Cadmium telluride is intensively studied lately as a promising material for photonics. For applications it is necessary to have a semiconductor with low concentration of charged scattering centers. In this work we report an interesting phenomenon of lowering of charged scattering centers concentration in CdTe crystals doped with gadolinium. Single crystals of undoped CdTe and CdTe:Gd were grown by Bridgman method in the same technological conditions. The concentrations of A2 (E2=0.12-0.15 eV), A1(E1=0.05 eV) acceptors and compensating donors in the crystals were determined from the studies of Hall-coefficient and carriers mobility temperature dependences (T=80-420K). It was found that the concentration of A1-acceptors in CdTe:Gd was essentially smaller than that in undoped CdTe. At the same time concentration of compensating donors was also lowered. The effect takes place at doping with gadolinium in concentration N>10^18 cm^(-3). Thus Gd impurity does not bring new electrical active centers into CdTe lattice while residual impurities concentration is lowered. We suggest that Gd impurity intensifies the formation processes of Te enriched precipitates which act as the getters for shallow acceptors and donors. The possibility of this intensification is caused by the existence of several chemical compounds and eutectics in Gd-Te systems. Further self-purification of CdTe:Gd crystals takes place under long-term thermal treatment at 380-440°C temperatures.

Authors : Yoon Shon, H. C. Jeon, Sejoon Lee, T. W. Kang( Quantum Functional Semiconductor Research Center, Dongguk University, Seoul 100-715, Korea); Eun Kyu Kim(Department of Physics, Hanyang University, Seoul 133-791, Korea); D. J. Fu and X. J. Fan(Department of Physics, Wuhan University, Wuhan 430072, P. R. China); Chong S. Yoon (Department of Materials Science and Engineering, Hanyang University, Seoul 133-791, Korea); Jeoung Ju Lee(Department of Physics, Gyeongsang National University, Jinju 660-701, Korea)
Resume : In the case of diluted magnetic semiconductor for spintronics, the study of Mn metal-incorporated InMnP codoped with Zn is new and promising. The p-type InP:Zn was prepared by the liquid encapsulated Czochralski method and subsequently implanted with Mn+ of 5  1015 cm-2. The results of energy dispersive x-ray displayed that the concentration of incorporated Mn into InP:Zn is about 1 at%. The cross-sectional transmission electron microscopy image of Mn+-implanted InMnP:Zn showed that the thickness of Mn-incorporated layer is ~ 300 nm. Auger electron spectoscopy(AES) was measured in order to investigate the morphology of Mn+-implanted InMnP:Zn. For photoluminescence measurements, the Mn-related optical transitions caused by incorporation of Mn were broadly observed at the energy region of 1.034, 0.985, and 0.958 eV. The samples clearly showed ferromagnetic hysteresis loops at 10 K, and the ferromagnetic behavior was observed to persist up to 360 K. Thus, the Curie temperature of Mn+-implanted InMnP:Zn (Mn ~ 1 at%) is expected to be above 300 K. It is found that a room-temperature-ferromagnetic semiconductor of InMnP:Zn can be formed by ion implantation of a relatively low concentration of Mn (1 at%).

Authors : Yu-Chun Li, Yee-Shin Chang, Yu-Cheng Lai, Yi-Jing Lin1, Chih-Hao Laing, Yen-Hwei Chang
Resume : The novel Phosphors of LaAlGe2O7 doped with Gd3+ and Tb3+ were synthesized and their luminescence properties have been investigated. In Tb3+-activated LaAlGe2O7, the extraordinary excitation spectra showed only intense f-f transition of Tb3+ ions around near-UV region, while the 4f-5d transition could be neglected. In Gd3+-Tb3+ system, time-resolved spectra exhibit a “grow-in” behavior, which indicates that the decay curves have a contribution from a Gd3+-to-Tb3+ energy transfer pathway. In response to Gd3+ excitation at the 6IJ energy levels, the 5D4 decay time-resolved spectra exhibited a “grow-in” behavior as the Tb3+ concentration was diluted (<0.03 mol), while only a simple exponential decay could be observed at higher (>0.05 mol) Tb3+ concentrations. Two linear relationships were found between the energy transfer probability (PGd→Tb) and the Tb3+ concentration, which is clear evidence that there were two kinds of efficient Gd3+ to Tb3+ energy transfer processes in terms of Tb3+ concentration.

Authors : António Moreira dos Santos‡†, Luís D. Carlos‡ and João Rocha† ‡- University of Aveiro, Physics Department, CICECO, 3810-193 Aveiro, Portugal †-University of Aveiro, Chemistry Department, CICECO, 3810-193 Aveiro, Portugal
Resume : Electrical materials incorporating lanthanide ions have great potential as electro-optical multifunctional systems. Polycrystalline NASICON fast-ion conductors (Na5LnSi4O12, Ln= Eu, Tb) have been prepared via solid-state synthesis. These materials have been characterized by photoluminescence spectroscopy, including steady-state emission and excitation spectra, and measurement of the lifetimes of the excited states. Two Eu3+ sites have been detected: (i) in regular framework positions, and (ii) replacing Na+ ions in the tunnels. The assignment of each of the Eu3+ sites was possible by applying time resolved spectroscopy and line shape analysis. Samples containing only Eu3+ or Tb3+ emit mainly from one transition, respectively, 5D0→7F2 (610 nm, red) and 5D4→7F5 (550 nm, green), resulting in phosphors with bright red and green emission. Mixed lanthanide samples, Na5Tb0.25Eu0.75Si4O12 and Na5Tb0.75Eu0.25Si4O12, have also been prepared and efficient Tb→Eu energy transfer has been observed for the latter.

Authors : Yoon Shon, H. C. Jeon, C. S. Park, T. W. Kang (Quantum-functional Semiconductor Research Center, Dongguk University, Seoul 100-715, Korea); Eun Kyu Kim(Department of Physics, Hanyang University, Seoul 133-791, Korea); D. J. Fu (Department of Physics, Wuhan University, Wuhan 430072, P. R. China); J. J. Lee (Department of Physics and Research Institute of Natural Science, Gyeongsang National University)
Resume : Undoped GaN epilayers were prepared by molecular beam epitaxy(MBE) and subsequently implanted with the Mn+ of 1 and 10 at%. P-type GaN epilayers were grown by metalorganic chemical vapor deposition (MOCVD) and subsequently implanted with the Mn+ of 5 and 10 at%. Our aim is the characteristic comparison between Mn+-implanted materials after the growth of the undoped GaN by MBE and the p-type GaN codoped with Mg by MOCVD, respectively. The results of energy dispersive x-ray peaks displayed the Mn+-implanted concentrations of 1, 5, 10 at%, respectively. X-ray diffraction patterns showed that the undoped and p-type GaN epilayers annealed at 700 ~ 900oC with the Mn+ of 10 at% revealed the shoulder peaks of GaMnN, together with GaN(002) peaks. In relation to Mn-activation, it was confirmed that the photoluminescence peak at 2.5 eV in a donor-Mn acceptor transition(D-A pair) and the photoluminescence peak around 3.0 eV is a conduction band – Mn acceptor transition. Based on above results, magnetic properties were characterized by superconducting quantum interference device magnetometer. The undoped and p-type GaMnN epilayers measured at 10 K with the Mn concentration of 10% showed clear ferromagnetic hysteresis loop with increasing annealing temperature and ferromagnetic behavior persisting up to 300 K. However, the magnetic properties of the p-type GaMnN were enhanced in comparison with those of the undoped GaMnN. And also, the p-type GaMnN epilayer with the Mn concentration of 5% showed weak and unstable ferromagnetic hysteresis loop, but the undoped GaMnN epilayers with the Mn concentration of 1% did not show ferromagnetic hysteresis loop at all. Consequently, the characteristics of the Mn+-implanted GaMnN epilayers after the growth of p-type GaN codoped with Mg by MOCVD are totally better than those of the Mn+-implanted GaMnN epilayers after the growth of undoped GaN by MBE when Mn+ was inserted into compound semiconductor GaN in both cases.

Authors : A. Og. Dikovska, P. A. Atanasov, I. G. Dimitrov Institute of Electronics, Bulgarian Academy of Sciences,Tsarigradsko shose 72, Sofia 1784, Bulgaria
Resume : The optical and luminescent properties of rare-earth ions doped materials have attracted considerable interest in connection with the development of high-performance optoelectronic devices. The aim of the present study was to fabricate thin film Y2O3 waveguide amplifier at 1.5 m by pulsed laser deposition. Optically active Er, Yb co–doped Y2O3 films were grown on YAG substrates from a ceramic target. Special attention was paid to the waveguide characteristics and luminescent properties of the films. The waveguide losses (of about 1 dB/cm at 633 nm) and transversal intensity distribution profile of the guided mode were measured. The PL spectrum around 1.5 m was observed using excitation of the Er3+ ions by cross–relaxation of Yb3+. The measurement of the amplification was performed by prism-coupling of 1.5 m probe beam into a waveguide and monitoring its intensity and temporal response as the waveguide was optically pumped by a 980 nm excitation source. Infrared-to-visible up-conversion was also observed. However, it did not have a significant effect on the PL performance in the IR range of spectrum.

Authors : V.B. Shmagin, A.V. Lyutov, D.Yu. Remizov and Z.F. Krasilnik Institute for Physics of Microstructures, Russian Academy of Sciences, GSP-105, Nizhny Novgorod 603950, Russia
Resume : A study of radiation from silicon doped with erbium is of great importance due to possible applications to the modern silicon industry. In addition the nature of effects accompanying Er3+ luminescence from Si is of interest in itself. We describe new data on abnormal increase in erbium electroluminescence (EL) with temperature from silicon p-n junctions emitting under reverse bias. After Hansson et al., we presume that this phenomenon is caused by the changes in the p-n junction breakdown mechanism but in contrast to them we connect it with the changes in the pumping current distribution over p-n junction area. We demonstrate how the decrease in temperature produces the transformation of the tunnel p-n junction breakdown to the avalanche one and as a consequence the transformation of the uniform EL pumping at higher temperatures to the drive current pinching at lower temperatures. In our opinion the effect under study should be interpreted as an additional EL quenching occurring at lower temperatures due to the drive current pinching. Finally the EL temperature dependence is determined by the stronger quenching factor: i) connected with the nonradiative Er3+ relaxation and growing with increasing temperature or ii) connected with the drive current pinching and growing with decreasing temperature. LEDs under study were grown completely by Sublimation MBE technique. The work has been partially funded by RFBR (06-02-16563). G.V. Hansson et al. Appl.Phys.Lett. 78, 2104 (2001).

Authors : K. D. Vernon-Parry and J. H. Evans-Freeman MERI, Sheffield Hallam University P. Dawson Physics Dept, University of Manchester
Resume : We have investigated PL decay from Er implanted into SiGe/Si quantum wells (QWs) grown by molecular beam epitaxy (MBE), as well as Er implanted into Si control samples. Efficient PL from confined states in the strained MBE QWs before the Er implant confirmed that there was little or no non radiative recombination. One set of QWs had Er grown-in during MBE growth. The Er concentration in all QWs was of the order of 4 x 10^18cm-3. The implanted QW sample was re-grown at 550°C for five hours and XRD after re-growth showed that a high degree of strain had been retained. Er PL at 1.54microns was more intense from all QWs than in the implanted Si control but the PL lifetime was somewhat shorter suggesting that the excitation efficiency is improved when QWs are present but the recombination efficiency is reduced. When the excitation laser power density was increased by ten times, the PL decay of the Er in the quantum well structures was largely unaffected, but the PL decay time of Er in Si reduced. In the Si, photo-generated carriers were not confined and more are available to sample competing non-radiative paths throughout the crystal. In the QWs, photo-generated holes were confined as the majority of the band discontinuity occurs in the valence band, therefore the holes were not free to sample other recombination routes. The presence of a long lived hole population is suggested to increase the potential for efficient emission from Er in Si-based structures.

Authors : N. Vivet, M. Morales, M. Levalois, X. Portier Laboratoire SIFCOM-Ensicaen 6 Bd Maréchal Juin 14050 caen cedex J. L. Doualan Laboratoire CIRIL - Ensicaen, 6 Bd maréchal juin 14050 caen cedex
Resume : With the aim of realizing an electrically pumpable mid-infrared microlaser, Cr2+: ZnSe films have been grown at room-temperature by radiofrequency (rf) magnetron co-sputtering of a silica target covered with ZnSe and chromium chips. Various substrates such as [100]-GaAs and [100]-Si and glass have been used, and the chromium quantity incorporated has been monitored by varying the amount of chromium chips and the sputtering power in the 150-250W range. The structural characterizations of the films have been performed by means of transmission electron microscopy and X-ray diffraction studies. Whatever the chosen substrate, the films crystallize in the cubic zinc-blende structure and exhibit a high <111> texture orientation associated with a systematic elongation of anisotropic crystallites along the [111] direction. Besides, a few amount of ZnSe wurtzite structure is also evidenced in the films. Photoluminescence (PL) experiments reveal that the shape of PL spectra are comparable to that reported for bulk materials, indicating that Chromium is incorporated in the optically active Cr2+ state. The intensity of the mid-infrared emission at about 2.2 µm have been studied at various temperatures and excitation powers as a function of chromium concentration under direct (1.85 µm) and indirect (370-514 nm) excitations. This study showed that rf sputtering can provide viable structures for the realization of optically and future possibly electrically mid-infrared microlaser.

Authors : S. Müller, S. Geburt, W. Dewald, D. Stichtenoth, C. Ronning, II. Physikalisches Institut, Georg-August Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany J. Wang, Q. Li, Department of Physics, Chinese University of Hong Kong, Shatin, Hong Kong
Resume : Wires of semiconductor materials with diameters in the nanometer range can be easily grown by a so called vapour-liquid-solid (VLS) mechanism. Especially nanowires out of zinc oxide (ZnO), a direct wide band gap semiconductor with a large excitation binding energy, are promising candidates for applications in sensing, field emission as well as in optoelectronics. The simple geometry of such nanowires could act as cavity; therefore, rare earth doped ZnO nanowires may be very suitable for lasing issues. ZnO nanowires were grown using a vapour transport method, dispersed in Isopropanol and spincoated on clean Si substrates. Yb was introduced by ion implantation with a box like profile at different fluences. The implantation damage was removed by annealing at 700°C in an oxygen ambience for 30 min. EELS and EDX confirm the incorporation of the rare earth elements. The photoluminescence measurements showed sharp intra-4f-transitions of the Yb3+ levels with low quenching up to room temperature. The power dependent measurements indicate stimulated emission of these intra-4f-transitions. These luminescence properties will be discussed in this presentation and compared with identically doped ZnO bulk single crystals.

Authors : E. Cattaruzza, F. Gonella, G. Peruzzo Dipartimento di Chimica Fisica, Università Ca` Foscari Venezia, Dorsoduro 2137, 30123 Venezia, Italy A. Quaranta Dipartimento di Ingegneria dei Materiali e delle Tecnologie Industriali, Università di Trento, 38050 Povo, Trento, Italy C. Sada, E. Trave Dipartimento di Fisica, Università di Padova, via Marzolo 8, 35131 Padova, Italy
Resume : The ion exchange process is used in several materials application fields for introducing high dopant doses into glass. In this frame, field-assisted techniques are particularly interesting, allowing the penetration of multivalent ions which could not diffuse into the glass matrix by simple thermal drive. In the presented experiments, field-assisted ion diffusion of erbium in silicate glasses was performed for the first time, with the aim to define suitable methodologies for the controlled Er-doping of glasses, with application in the field of rare earth doped photonic materials for light amplification. Metallic erbium films deposited onto the substrates by the rf-sputtering technique were used as the metal ions source. Secondary ion mass spectrometry indicates a partial diffusion of erbium into the silicate glass matrix (soda-lime glasses), depending on the electric field and the process temperature values, and a corresponding migration of alkaline species already present in the glass. Photoluminescence emission at 1.54 microns was also determined in the prepared samples.

Authors : L.Bodiou, A. Braud, M.Wojdak, J. L. Doualan R. Moncorgé,CIRIL-ENSICAEN, CNRS UMR 6637, 6 boulevard Maréchal Juin, 14050 Caen cedex 4, France P. Ruterana, P. Marie, SIFCOM, UMR6176, 6 boulevard Maréchal Juin, 14050 Caen, France L. Méchin, GREYC, CNRS UMR 6072, 6 boulevard Maréchal Juin, 14050 Caen, France H. M. Ng,Bell Laboratories, Lucent Technologies, 600 Mountain Avenue, Murray Hill, NJ, USA
Resume : We investigated the photoluminescence (PL) and electroluminescence (EL) properties of a GaN:Er based device. It was found that 1.54µm PL spectra obtained with above- and below-band-gap excitation and the EL spectrum are similar. Green and infrared EL were observed at room temperature in the vicinity of the negatively biased contact. Voltage dependence of the EL intensity shows voltage thresholds of 12.5V and 5V for the green and infrared emissions respectively. The predominant excitation mechanism seems to be the impact excitation of Er3+ ions by hot electrons, which are injected and accelerated by the electric field. However, above the voltage thresholds both emissions exhibit different dependencies on the applied voltage, indicating that the excitation mechanisms for both emissions are different. Besides the dependence of both luminescence as a function of temperature also shows clear differences. In order to investigate in details these differences we used specific experiments combining simultaneously both electrical excitation and optical illumination. This type of experiments enables us to discriminate indirect Er excitation processes mediated by carrier traps compared to direct impact excitation of Er3+ ions by hot electrons.

Authors : P. Miska1, H. Rinnert1, V. Brien2, P. Pigeat2, 1 Université Henri Poincaré Nancy 1, Laboratoire de Physique des Matériaux, UMRCNRS 7556, Faculté des Sciences et Techniques, Boulevard des Aiguillettes, B.P. 239, F﷓54506 Vandoeuvre-lès-Nancy Cedex, France 2. CNRS, Laboratoire de Physique des Milieux Ionisés et Applications, UMRCNRS 7040, Université Henri Poincaré Nancy 1, Faculté des Sciences et Techniques, Boulevard des Aiguillettes, B.P. 239, F-54506 Vandoeuvre-lès-Nancy Cedex, France
Resume : Rare earth doping of wide-band gap III-V semiconductors are promising materials for electroluminescent devices, for instance flat panel displays. More specifically, Er3+ doped AlN materials are expected to provide great advances in the development of temperature insensitive Light Emitting Diodes for telecommunications applications at 1.54 mm. The mechanism of optical emission of such materials is not fully understood yet. However, some authors1 observed that the morphology (crystallography, size of grains) of the semiconductor matrix has non-negligible effects on the optical emission. As ultra high vacuum radio frequency magnetron sputtering has recently shown to be able to produce AlN films with various well-controlled nanostructures2, the authors prepared nanostructured AlN:Er films with different Erbium contents with this technique. The first Transmission Electron Microscopy, Electron Dispersive Spectroscopy of X-rays and photoluminescence characterizations of this study will be presented. Precise characterizations of structure, crystalline morphology and stoichiometry were done, and the authors will discuss the correlation between the morphology, the Erbium content and the optical results. References : 1. A.R. Zanetta, Applied Physics Letters 82, 1395 (2003) 2. V. Brien, P. Pigeat, Microstructures diagram of magnetron sputtered AlN deposits : amorphous and nanostructured films, To be published in Journal of Crystal Growth (2007)

Authors : A. Lazreg (*), Z. Dridi (*), F. Benkabou (**), B. Bouhafs (*), and P. Ruterana (***) (*) Modelling and Simulation in Materials Science Laboratory, Physics Department, University of Sidi Bel-Abbes, 22000 Sidi Bel-Abbes, Algeria. (**)Departement de physique et d\'astronomie, Facultes des sciences, Universite Moncton, Moncton, NB E1A 3E9, Canada. (***)SIFCOM UMR 6176 CNRS-ENSICAEN, 6 Boulevard Marechal Juin, 14050 Caen Cedex, France.
Resume : First-principles calculations, by means of the full-potential augmented plane wave method using the local spin-density approximation, were carried out for the electronic and magnetic properties of MnN and the diluted magnetic alloys Ga0.75Mn0.25N in zinc-blende structure. We discuss the electronic structures, density of states, local magnetic moments, and exchange interactions. These ferromagnetic compounds are found to be half metallic materials. For Ga0.75Mn0.25N, the valence band is ferromagnetically coupled to the Mn atoms. The total magnetization of the cell is estimated to 4.0 B.

Authors : A. Podhorodecki,* M. Nyk and J. Misiewicz Institute of Physics, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland W. Strek Institute of Low Temperature and Structure Research, Polish Academy of Sciences P.O. Box 1410, 50-950 Wroclaw 2, Poland
Resume : Gallium nitride (GaN) nanocrystalline powder doped by europium ions at different concentration (0.5-2%) has been obtained by combustion method at 1050oC nitridation temperature. It has been found that this temperature gives high quality hexagonal crystalline structure of pure GaN nanocrystalls with diameter about ~30 nm. Structural and optical properties of GaN nanocrystalline powder, doped by europium ions have been investigated by X-ray diffraction and photoluminescence measurements. It has been found that doping GaN nanocrystals by europium ions reduce the nanocrystals diameter for small (0.5%) and high (2%) ions concentrations and increase nanocrystalls diameter for medium concentrations (1-1.5 %). It has been also found that depending on europium concentrations optical properties (and optical quality) of GaN:Eu3+ nanocrystalline powder changes significantly. In all samples, strong and narrow UV emission band centered at ~3.4 eV has been observed. Also strong emission band related to defects in GaN has been observed at ~2 eV. Moreover, emission bands related to europium f-f transitions partially, depending on Eu3+ concentration, covered by defect related emission band have been also observed. It has been also observed, that with increasing of europium concentration other GaN related defect states became optically active. Thus, in this work all these effects will be present and discuses.

Authors : D. Maouchea,1; P. Ruteranab,2 ; and L. Louaila. aDepartment of physics, Faculty of Sciences, University of Setif, Algeria bSIFCOM, UMR6176, CNRS-ENSICAEN, 6 Bld Mar?al Juin, Caen 14050, France
Resume : During recent years, rare earth or transition metal doped large band gap semiconductors (GaN, ZnO) are under intensive investigation for possible spin sensitive photonic applications at room temperature, in this vein Mn-doped ZnO which is anti-ferromagnetic spin glass state, has been shown to become ferromagnetic upon hole doping. In this wok we investigate (Zn,Mn)O codoped with N in order to determine how this modifies the ground state from antiferromagnetic to ferromagnetic. Our approach is based on the spin-polarized relativistic Korringa–-Kohn–Rostoker (SPR–KKR) density functional theoretical (DFT) method, within the coherent potential approximation (CPA ). Self-consistent electronic structure calculations were performed within the local density approximation, using the Vosko-Wilk-Nusair parameterization of the exchange-correlation energy functional. We show that by codoping with N and Mn, it is possible to turn ZnO into a dilute magnetic semiconductor. The results show that spin glass (SG) order is energetically more favoured than ferromagnetic (FM) order in Mn-doped ZnO with x=0.05. In 15%, 20 % and 25% concentrations of Mn-doped ZnO, the FM interaction dominates in all ranges of nitrogen concentrations, while for Mn-doped ZnO concentrations of 10%, the FM states do not exist with a nitrogen concentration of 5% and 10%.

Authors : F. Gloux1, P. Ruterana1, , K. Lorenz2 and E. Alves2 1SIFCOM, UMR 6176, CNRS-ENSICAEN, 14050 Caen, France 2Instituto Tecnol?o e Nuclear, EN10, 2686-953 Sacav? Portugal
Resume : Rare earth (RE) doped GaN is the subject of on going research due to expected applications in photonics. The use of ion implantation is of high interest for its compatibility with industrial production, the possibility to control the lateral distribution of REs and to perform easy multiple REs integration. However, implantation leads to structural damage in the GaN structure. In order to reduce the amount of induced implantation damage, one solution is to implant at elevated temperatures. Unfortunately, it was reported that such implantation leads to erosion of GaN. Interestingly, it was also shown that a thin epitaxial AlN cap on GaN with optimized conditions may prevent from the surface erosion induced by implantation performed at RT and the subsequent high temperature annealing. In this work, we investigated the behaviour of AlN protected GaN layers during the implantation at 500°C. For this we carried out a comparative study of the structural damage induced in capped and uncapped GaN layers, at 300keV in the fluence range [1-20]?015RE/cm2. Such layers have also been annealed at 1300°C, we will discuss the resulting microstructure.

Authors : E. van der Kolk (e.vanderkolk@tudelft.nl), P. Dorenbos, Delft University of Technology, 2629JB Delft, The Netherlands
Resume : New Lanthanide (Ln) doped materials for photonic applications such as lasers, wide bandgap electroluminescent devices, LED phosphors, scintillator detectors, etc. are continuously being developed. Material discovery usually proceeds via guided trial and error with time consuming material preparation and laboratory characterization. Design of materials, with deliberately chosen properties, through ab initio or phenomenological modeling will certainly accelerate discovery. Considerable progress has been made in the past years in developing models describing the energy of the Ln-ion 4f and 5d-states, either parameter based [1], ab initio based [2-3] or empirical based [4-5]. These models predict the energy of the 5d-states relative to the 4f-states as a function of the type of Ln-ion of the Ln-series (La,Ce,Pr,..,Lu). These models were recently complemented with an empirical model that describes the energy of the 4f and 5d-states relative to the valence and conduction band of the host [6]. In this contribution an empirical model for stoïchiometric (fully concentrated) lanthanide materials (like CeO, Ce2O3, CeO2) is presented that describes a systematic and material independent variation of the electronic structure over the Ln-series. The model is derived from experimental data on 4f and 5d-energies of Ln-ions as impurities in (luminescent) materials but, as will be shown, can fruitfully be applied to stoïchiometric Ln-materials [7]. The validity and usefulness of the model is demonstrated by application to the Ln-sulfides and the well known Ln-oxides LnO, Ln2O3, and LnO2 for which the model correctly predicts insulating, semi-conducting or metallic behavior, nature and magnitude of band-gap energies and chemical stability of Ln-materials as well as valence and valence changes of Ln-ions. The model may serve as a reliable tool to accelerate design of a broad range of Ln-materials with deliberately chosen properties. [1] Van Pieterson L, Reid M.F, Wegh R.T, Soverna S, Meijerink A. Phys. Rev B. 65 (4): Art. No. 045113 (see also Art. No. 045114). [2] Andriessen J, Dorenbos P, van Eijk C.W.E, Phys. Rev. B 72 (4): Art. No. 045129 (2005). [3] Marsman M, Andriessen J, van Eijk C.W.E, Phys. Rev. B 61 (24): 16477-16490 (2000). [4] Dorenbos P. J. Lum. 91 (2000) 91 (ibid. 155). [5] Dorenbos P. J. Phys. Cond. Matter 15, 575 (2003). [6] Dorenbos P. J. Lum. 108, 301 (2004). [7] Van der Kolk E, Dorenbos P, Chemistry of Materials, 18 (15) 3458-3462 (2006).

Authors : Y. Luo, X. Multone, C. N. Borca, P. Hoffmann Advanced Photonics Laboratory, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland
Resume : Large-scale fabrication of functional devices from thin oxide film has attracted great interest in the fields of electronics and optics. We successfully deposited amorphous alumina (Al2O3) thin films by high vacuum chemical vapor deposition (HV-CVD), with high homogeneity in thickness over the entire surface of a 6 inch wafer. Alternatively in a combinatorial deposition approach, a large number of different samples are produced on one single 4 inch wafer. By means of photolithography followed by reactive ion etching, channel waveguides have been obtained from the deposited planar alumina waveguide films on an 8 um thick silica buffer layer. The width of the waveguides ranges from 2 to 10 um, with a freely chosen length between several micrometers to the full wafer diameter (10 cm). Passive wave-guiding properties have been demonstrated in as-deposited alumina thin film as well as in the micro-structured channels, for several wavelengths up to the telecom window. The propagation loss in both planar and channel waveguides has been evaluated to a high precision by optical low coherence reflectometry (OLCR) in the reflection mode. The results are important for the application of passive and active channel waveguide devices. The optical influence of co-deposited rare-earth ions (such as Er or Yb) in the alumina film during the HV-CVD procedure will also be discussed.

Authors : A. I. Chroneos1,2 and I. L. Goulatis3 1 Imperial College London, Department of Materials, London, SW7 2BP, UK 2 NCSR Demokritos, Institute of Microelectronics, Aghia Paraskevi 15310, Greece 3VN Karazin Kharkov National University, 4 Svobody Sq., UA - 61077 Kharkov, Ukraine
Resume : Electronic structure simulation techniques have been used to study the stability of erbium-vacancy and aluminium-vacancy complexes in germanium carbide (GeC). The calculations used a plane-wave basis set and pseudo-potentials within the generalized gradient approximation (GGA) of density functional theory (DFT). GeC is being considered as a promising alternative material for photovoltaic and other electro-optic applications. This is partly because the addition of carbon in germanium results to the increase of the band gap and reduces the lattice parameters thus allowing the ordered growth on silicon substrates. The incorporation of dopants such as aluminium in GeC decreases the crystallinity but enhances the photon absorption and therefore is important for the optoelectronic properties of the material. In the present work the erbium-vacancy and aluminium-vacancy complexes in GeC have been studied in detail. The calculations indicate the important differences in the stability of the erbium-vacancy and aluminium-vacancy complexes in GeC.

Authors : F. d\'Acapito ($), C. Maurizio ($), P. Mukul (*), Th. S. Lee (*), W. Blanc (*), B. Dussardier (*) ($) CNR-INFM-OGG c/o ESRF, 6 Rue Jules Horowitz, F-38043 Grenoble France. (*) LPMC, UMR6622 CNRS / Université de Nice - Sophia Antipolis, F-06108 Nice, France
Resume : Rare-earth (RE)-doped optical fiber based devices, such as lasers or amplifiers for telecommunications have recently experienced tremendous progress. Silica-based fibers are cheap, reliable and able to sustain extremely high optical densities, compared to other alternative glasses. However silica has a low solubility for RE ions, and often provides low quantum efficiency to some interesting RE optical transitions, mostly due to high local phonon energy. Hence, we explore the potential of encapsulating RE ions in nanoparticles (NP) within the fiber glass, in order to provide them with specific local compositional and/or structural environment. Our preparation technique is based on commercially available MCVD (Modified Chemical Vapour Deposition) associated to \"solution doping\". Fiber preforms of composition SiO2-GeO2-P2O5-Er2O3 with and without CaO have been investigated by x-ray absorption spectroscopy (XAS) to evidence the role of Ca in the incorporation site for Er in the glass. A XAS study at the Er-LIII edge has been carried out at the GILDA beamline at the ESRF. In absence of CaO, Er locates in the highly symmetric P-related cages which exhibit a local geometry similar to that in ErPO4. No NP were evidenced by Transmission Electron Microscopy (TEM) in these samples. On the other hand, when CaO is present in the glass, TEM shows the presence of amorphous particles that contain most of the Er3+ ions and, correspondingly, XAS shows that Er is in a glassy environment.

Authors : A. Najar 1,2, J. Charrier1, H. Ajlani2, N. Lorrain1, S. Haesaret1, M. Oueslati2, L. Haji1
Resume : Erbium-Ytterbium co-doped porous silicon planar and buried waveguides were prepared from P+-type silicon. Erbium (Er3+) and Ytterbium (Yb3+) ions were electrochemically introduced at different Yb3+ concentrations. The doping profiles of erbium and ytterbium ions were determined by EDX analysis performed on sample cross section. The mean concentration in the guiding layer closed 1020 cm-3. The refractive indices were measured from co-doped porous silicon before and after the thermal treatments of oxidation and dopant activation. The photoluminescence (PL) peak of optically activated erbium ions at 1,53 µm was recorded. Its intensity depends of the Yb3+ concentration due to the Yb3+ Er3+ energy resonant transfer at 0.98 µm. Optical losses at 1.53 µm were measured on these waveguides and were about 1.7 dB/cm. The optical gain at 1,53 µm with copropagating pump at 0.98 µm in these waveguides was determined and discussed for various Er3+/Yb3+ ratio.

Authors : Antoine Al Choueiry, Anne-Marie Jurdyc, Bernard Jacquier (1), Frederic Lacour, Nathalie Herlin (2), Corinne Chanéac (3) 1 : Laboratoire de Physico Chimie des Matériaux Luminescents Lyon1, 10 rue André Marie Ampère 69622 Villeurbanne France, choueiry@pcml.univ-lyon1.fr, jurdyc@pcml.univ-lyon1.fr, jacquier@pcml.univ-lyon1.fr 2 : Service des Photons Atomes et Molecules, Laboratoire Francis Perrin (CEA-CNRS URA 2453), Bat 522 CEA Saclay - 91191 Gif/Yvette Cedex, frederic.lacour@cea.fr , nathalie.herlin@cea.fr , 3 : Laboratoire de Chimie de la Matière Condensée Paris VI chaneac@ccr.jussieu.fr
Resume : In the last decade, an intense research activity has been devoted to use erbium doped silicon nanocrystals (Si-Nc) for optical amplification around 1.54µm wavelength range. Energy transfer process between silicon microclusters and erbium ions have been discover by Kenyon1 in 1994. Recent studies have shown the possibility of optical gain at 1.5µm in planar waveguide2 doped by Si-Nc and erbium ions, but to our knowledge no optical fibres doped by Si-Nc and erbium ions have been elaborated for the moment. The aim of our work is to prove the feasibility to insert Si-Nc in optical fibre by controlling the optical properties of Si-Nc in all process stages (from as synthesized Si-Nc powder to a silica fibre doped with Si-Nc). Si-Nc elaborated by laser pyrolysis of silane in a gas flow reactor were dispersed in a silica matrix by sol gel technique. Additional doping with erbium was performed for some samples to investigate energy transfer process. We have performed a detailed study of the optical properties and temporal behavior of Si-Nc in gel matrix treated at different temperature and under different gas atmosphere. For gel samples codoped with Si-Nc and erbium we observe a week energy transfer probably because the erbium ions were far from Si-Nc. Efforts are done currently to optimize the interaction distance between Si-Nc and erbium by controlling the elaboration process. 1 A. J. Kenyon et al, J. Phys. Condens. Matter, 6 (1994), 319 2 H. Lee et al, Optics express 13 (2005), 9981

Authors : B. González-Díaz (1), B. Díaz-Herrera (1), J. Méndez Ramos (2), V.D. Rodríguez (2), C. Hernández-Rodríguez (1), R. Guerrero-Lemus (1) and J.M. Martínez-Duart(3). (1)Departamento de Física Básica. Universidad de La Laguna. Avda. Astrofísico Francisco Sánchez. 38204 La Laguna. S/C de Tenerife. Spain. Tel. +34922318306, Fax. +34922318228, rglemus@ull.es. (2)Departamento de Física Fundamental, Experimental Electrónica y Sistemas. Universidad de La Laguna. Avda. Astrofísico Francisco Sánchez. 38204 La Laguna. S/C de Tenerife. Spain. (3) Departamento de Física Aplicada, C-XII. Universidad Autónoma de Madrid. 28049 Cantoblanco. Madrid. Spain. Tel. +34914974509, Fax. +34914973969, martinez.duart@uam.es
Resume : In this work a simple erbium doping process applied to porous silicon stain etched surfaces is proposed. This doping process has been developed for application in porous silicon solar cells, where conventional erbium doping processes are not affordable because of the high processing cost (ion implantation), technical difficulties (epitaxy) or the long processing times (sol-gel). The porous silicon layers (PSL) were formed by immersion in an aqueous solution of HF/HNO3 with different concentrations for properly matching the porosity and pore thickness to an optimal doping of the porous structure. After the formation of the porous structure, the PSL were analyzed by means of nitrogen BET area and scanning electron microscopy. Next, the PSL were immersed in a saturated erbium solution in order to cover the porous surface. After this process, the samples were subjected to a thermal process to activate the Er3+. Different temperatures and annealing times were used in this process. The photoluminescence of the PSL was evaluated before and after the doping processes. Moreover the composition of the porous surface was analyzed by means of a Fourier transform IR spectrometer.

Authors : M. Wojdak1, I. I. Liaw2, I. Ahmad1, C. J. Oton3, W. H. Loh3, A.J. Kenyon1, I. W. Boyd2 1 Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE, United Kingdom 2 London Centre for Nanotechnology, 17-19 Gordon Street, London WC1H 0AH, United Kingdom 3 Optoelectronics Research Centre, University of Southampton, SO17 1BJ Southampton, United Kingdom
Resume : Silicon-rich silica samples doped with erbium were grown by PECVD and characterised by photoluminescence, time resolved photoluminescence and Fourier transform infrared spectroscopy. We observe that upon increased silicon content, the absorption spectrum reveals the formation of a Si-N bond. This indicates the possible incorporation of nitrogen from the precursor N2O gas into the Si nanoclusters. The erbium emission is shown to increase with silicon content and results in decay times up to 5ms with nearly single exponential characteristics. In addition to erbium emission, a visible luminescence peak at about 550nm is observed. This shows multi-exponential decay kinetics with decay times of the order of 10ns. We propose that this emission is due to small Si nanoclusters covered by a Si-N shell. From the measurements, we study a mechanism to explain the erbium excitation in this material.

Authors : H. Touati, M. Souissi*, Z. Chine, A. Bchetnia, B. El jani Unité de Recherche sur les Hétéro-Epitaxies et Applications, Faculté des Sciences de Monastir 5000, Tunisie.
Resume : Photoluminescence (PL) of vanadium-doped GaN (GaN: V) has been studied. Samples were successfully prepared on sapphire substrates by metalorganic vapour phase epitaxy technique (MOVPE). A characteristic infrared luminescence band, dominated by a zero phonon line at 0.82 eV and a blue band at 2.6 eV has been observed. The temperature dependence of the spectra, which were measured from 9 K to 300 K, showed a decrease in the infrared intensity and an increase of visible emission intensity at room temperature.

Authors : J. Mayandi, A. Galeckas, S. Foss, T.G.Finstad, Dept. Physics and Centre Materials Science and Nanotechnology, University of Oslo Norway. M.Stange Materials and Chemistry, SINTEF, Oslo, Norway
Resume : We report on the fabrication of Si and Ge nanoclusters in Er doped Al2O3 films by RF sputtering and annealing. Samples with different concentrations Si and Ge respectively have been prepared. Control samples without Si and Ge in Al2O3 have also been prepared for comparison. We have studied the Er3+ (1.5µm) photoluminescence from these structures as a function of annealing temperatures from 500 – 1100 ºC in nitrogen ambient. The samples with Si show relatively intense Er luminescence compared to the control samples and also compared to the Ge case. For the Ge case the Er luminescence is even weaker than that of the control sample without Ge (containing Er and Al2O3). We have made additional structural studies on similar samples and intend to characterize the present sample set by HRTEM, XPS, XRD, and FTIR measurements to correlate with the trends of photoluminescence intensity

Authors : Marco Peres, Departamento de Fisica e I3N, Universidade de Aveiro, 3810-193 Aveiro, Portugal M. Macatrao Departamento de Fisica e I3N, Universidade de Aveiro, 3810-193 Aveiro, Portugal A. Lourenço Departamento de Fisica e Ciceco, Universidade de Aveiro, 3810-193 Aveiro, Portugal A.J. Neves, Departamento de Fisica e I3N, Universidade de Aveiro, 3810-193 Aveiro, Portugal M. J. Soares, Departamento de Fisica e I3N, Universidade de Aveiro, 3810-193 Aveiro, Portugal T. Monteiro, Departamento de Fisica e I3N, Universidade de Aveiro, 3810-193 Aveiro, Portugal E. Alves, Instituto Tecnologico e Nuclear, ITN, Estrada Nacional nº 10, 2686-953 Sacavem Portugal V. Munoz SanJose, Departamento de Fisica Aplicada, Universidad Valencia, Valencia, Spain F. Hosseini Teherani, Nanovation SARL, 103 bis rue de Versailles, 91400, France L. Divay, Universite Technologie de Troyes, 12 rue Marie Curie, Troyes, 10010, France D. J. Rogers, Nanovation SARL, 103 bis Rue de Versailles, Orsay, 91400, France. & Universite Technologie de Troyes, 12 rue Marie Curie, Troyes, 10010, France
Resume : Praseodymium implanted ZnO samples, including bulk crystals and thin films grown by MOCVD, PLD and RF sputtering on sapphire were studied by optical spectroscopy and structural techniques. Sharp emission lines due to intra 4fn shell transitions were observed near 6500A in photoluminescence spectra. We assign these lines, detected under below band gap excitation, to transitions between 3P0,1->3F2,3 levels of the Pr3 ion. We report on the temperature dependence of the intra-ionic emissions. The influence of the growth method and ion implantation fluence on the optical properties and structural quality of the samples is discussed. The implanted rare earth ion site location in bulk samples was analysed by random and aligned RBS measurements.

Authors : C. L. Heng, E. Chelomentsev, O. H. Y. Zalloum, and P. Mascher Department of Engineering Physics and Centre for Emerging Device Technologies, McMaster University, Hamilton, Ontario L8S 4K1, Canada
Resume : During the past decade, Er3+ photoluminescence (PL) at 1.54 µm from Er-doped Si-rich Si oxide (Er-SRSO) films has attracted great interest for the development of light sources or small-sized and Si-compatible optical amplifiers.1-4 Compared to the Er-SRSO system, light emission from Ge-doped SiO2 system are quite different,5 which may result in different luminescence properties when doped with Er ions.6 In this work, we have studied the PL from the SiO2 films co-doped with (Er, Ge) or co-doped with (Er, Ge and Si) to investigate excitation efficiency of Ge and/or Si nanoclusters to the Er PL. The films were deposited by magnetron sputtering composite target Ge+Er+SiO2 or Ge+Si+Er+SiO2 in a pure Ar ambient and excited using a non-resonant excitation of 325 nm He-Cd laser line. After annealing at 950 °C in N2 for 30 min., strong blue emission bands around 400 nm and near-infrared bands around 800-850 nm have been observed from the (Ge, Er) co-doped film, which are attributed to Ge-related defects and Ge nanoclusters, respectively; while the Er PL reaches the highest intensity after an 800 °C anneal. Our initial results demonstrate that the PL spectra from the (Er, Ge and Si) co-doped SiO2 film show different emissions behavior with increasing annealing temperature. This is attributed mainly to the gradual formation of Ge clusters, SiGe alloy and Si nanocrystals. A further study is in progress. This work has been supported by the Ontario Research and Development Challenge Fund under the auspices of the Ontario Photonics Consortium. 1. A. J. Kenyon, P. F. Trwoga, M. Federighi, and C. W. Pitt, J. Phys.: Condens. Matter. 6, L319 (1994). 2. A. Polman, J. Appl. Phys. 82, 1 (1997). 3. G. Franzò, V. Vinciguerra, and F. Priolo, Appl. Phys. A: Mater. Sci. Process. 67, 3 (1999). 4. T. Nakamura, M. Fujii, S. Miura, M. Inui and S. Hayashi, Phys. Rev. B 74, 045302 (2006). 5. L. Rebohle, J. von Borany, H. Fröb, W. Skorupa, Appl. Phys. B: Lasers and Optics 71, 131 (2000). 6. M. J. A. de Dood, J. Knoester, A. Tip, and A. Polman, Phys. Rev. B 71, 115102 (2005).

Authors : V.S.Gurin, Physico-Chemical Research Institute, Belarusian State University, Leningradskaya str., 14, 220080, Minsk, Belarus; A.A.Alexeenko, Gomel State Technical University, Gomel, Belarus
Resume : Various photonic applications of rare earth elements demand a possibility to control their luminescence features determined by their chemical and electronic states in compounds. One of useful type of emissive materials with rare earth ions is solid dielectric matrices with controllable optical properties, e.g. silica derived by various techniques. It is usable as good optical material (both films and glasses). In spite of much research activity in the field of matrix-stabilized rare earth ions, there remain the problems to produce desired electronic states of the multivalent ions, Eu(II)/Eu(III), Sm(II)/Sm(III), etc. A difference in the valence states has the dramatic effect upon emission properties. Meanwhile, chemistry of these elements allowing the redox-transformations in solutions is changed significantly in solid state when materials are fabricated at elevated temperatures. In the present work, we have collected our studies of rare earth ions in a series of silica-based materials demonstrating the possibility to control chemistry of these ions in the matrices and their luminescent properties. The redox-transformations were realized through solid-state reactions in a controllable gaseous media and interaction with second dopants. The method to manage the luminescence of the rare earth ions through physical effects was elaborated in the matrices with metal- and semiconductor nanoparticles absorbing light radiation due to own familiar mechanisms.

Authors : A.Sh.Abdinov, R.F.Babaeva, A.T.Bagirova
Resume : High photosensitivity of crystals InSe and GaSe at temperatures down to 300-350K in all visible and significant part of near IR region of optical spectrum makes their as perspective materials for creation of photovoltaic elements not demanding special cooling. However, presence in these semiconductors of simultaneously various dot and large-scale intrinsic defects cause low stability and reproducibility of their photoelectric parameters, and also parameters and characteristics of photovoltaic elements on their basis. By present time with the purpose of overcoming this lacks of the specified materials are undertaken various attempts. However the question has not found the exhaustive decision. In the present work the opportunity of control of a degree of disorder of crystals InSe and GaSe is investigated by alloying them with rare-earth elements (RE). Thus besides increase of a degree of stability and reproducibility of parameters, main attention has addressed also to expansion of photosensitivity contour of the photovoltaic elements. As a result of the carried out investigations, it is established, that by means of change of entered impurity percentage (NRE) can vary in the significant image as absolute size (down to 60-80 %), and photosensitivity spectrum contour (almost up to 25 %) both materials. moreover, the optimum values of NRE (10-1 аt.%) at which the greatest high degree of stability and reproducibility of parameters, and also characteristics of the elements photovoltaic is provided on the basis of these crystals.