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Epitaxial Layers (epitaxial + layer)
Kinds of Epitaxial Layers Selected AbstractsCombined structural and optical studies of stacking faults in 4H-SiC layers grown by chemical vapour depositionPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2009Maya Marinova Abstract The formation of in-grown stacking faults (SFs) in chemical vapour deposition (CVD) grown 4H-SiC epilayer has been studied by high-resolution transmission electron microscopy (HRTEM) and low-temperature photoluminescence (LTPL). Local inhomogeneities in the SF density have been found, where different SF arrangements appear. They range from pure 8H-SiC unit cells to a few distinguished sequences, forming in some cases long-range semi-periodic incommensurate structures. Despite such large dispersion, the same optical (LTPL) signature is always found. This is discussed in the light of coupled quantum well models. HRTEM image showing the formation of an extended defect (16 bilayers thick) in a CVD grown 4H-SiC epitaxial layer. [source] Atomic layer epitaxy of GaMnAs on GaAs(001)PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2007M. Ozeki Abstract A self-limiting mechanism in atomic layer epitaxy (ALE) has been investigated for the heterogrowth of GaMnAs on GaAs(001) substrate. In the ALE, trimethylgallium, bismethylcyclopentadienylmanganese and trisdimethylaminoarsine were used as source materials of gallium, manganese and arsenic atoms, respectively. Although the growth of GaMnAs was carried out at a high growth temperature of 500 °C, a distinct self-limiting mechanism was observed for the manganese alloy composition up to 6% and the epitaxial layer had no indications of including MnAs phase. The layer showed an atomically flat surface morphology reflecting the self-limiting growth. The self-limiting mechanism was largely affected by the lattice mismatch between GaMnAs epitaxial layer and GaAs substrate. When the manganese alloy composition exceeded 7%, the self-limiting mechanism was broken and MnAs precipitates were observed in the epitaxial layer. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] High performance Schottky UV detectors (265,100 nm) using n-Al0.5Ga0.5N on AlN epitaxial layerPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003H. Miyake Abstract A high responsivity spectrum in the near ultraviolet (UV) and the vacuum UV (VUV) region was realized using Schottky UV detectors consisting of Al0.5Ga0.5N on an AlN epitaxial layer. The cut-off wavelength of AlGaN UV detectors was 4.7 eV (265 nm), a value that corresponds to the band gap of Al0.5Ga0.5N. The contrast of responsivity between the near UV and the visible was about 104. The GaN Schottky detector hads a high responsivity region in the near-UV from 3.4 to 5.0 eV (250,360 nm), whereas the AlGaN UV detector had a high responsivity in the UV,VUV region from 4.7 to 12.4 eV (100,265 nm). From these results, the fabricated AlGaN-based UV photodetectors can likely be used in detectors for the UV,VUV region. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Localized biexcitons in AlxGa1,xN ternary alloy epitaxial layersPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003Y. Yamada Abstract Excitonic optical properties of AlxGa1,xN ternary alloy epitaxial layers have been studied by means of photoluminescence (PL), time-resolved PL, and PL excitation (PLE) spectroscopy. The luminescence line due to radiative recombination of biexcitons was clearly observed in an Al0.08Ga0.92N epitaxial layer. The PL decay time of excitons and biexcitons was estimated to be 350 and 210 ps, respectively. PLE spectroscopy of biexcitons enabled us to observe a two-photon absorption process of biexcitons. On the basis of the energy separation between exciton resonance and two-photon biexciton resonance, the binding energy of biexcitons in Al0.08Ga0.92N was estimated to be 15 ± 2 meV. This value was approximately 2.5 times as large as the binding energy of biexcitons in GaN. This value was also found to be comparable to the observed energy separation between the exciton luminescence and the biexciton luminescence, which indicated the strong localization of biexcitons. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Plasma assisted LED wafer scribing and fabrication of Ag nanoparticle-embedded LEDPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010Jong-Moo Lee Abstract Two applications of plasma effects in fabrication of LEDs are introduced. One is scribing LED wafer by mechanical impacts of plasma, which is induced by laser ablation, to the bottom of LED wafer. The other one is the surface plasmon effect on light emission. Ag nano-particles are formed on about 50-nm thick p-GaN epitaxial layer over multi-quantum wells (MQWs) and an additional 150-nm thick p-GaN layer is grown again over the surface. As the result, the Ag nano-particles are located within the overall p-GaN epitaxial layer, very near to MQWs. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] High power AlGaN/GaN HFETs on 4 inch Si substratesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009Nariaki Ikeda Abstract In this paper, we successfully demonstrate an AlGaN/GaN HFET with a high breakdown voltage on 4-inch Si substrates. In order to obtain the high breakdown voltage and to improve the crystalline quality of GaN layers, a thick GaN epitaxial layer including a buffer layer was grown. The breakdown voltage and the maximum drain current were achieved to be over 1.3 kV and 120 A, respectively. Furthermore, the suppression of a current collapse phenomenon was examined. The on-resistance was not significantly increased up to a high drain off-bias-stress of 900 V. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Growth of InN on 6H-SiC by plasma assisted molecular beam epitaxyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006April S. Brown Abstract We have investigated the growth of InN films by plasma assisted molecular beam epitaxy on the Si-face of 6H-SiC(0001). Growth is performed under In-rich conditions using a two-step process consisting of the deposition of a thin, low-temperature 350 °C InN buffer layer, followed by the subsequent deposition of the InN epitaxial layer at 450 °C. The effect of buffer annealing is investigated. The structural and optical evolution of the growing layer has been monitored in real time using RHEED and spectroscopic ellipsometry. Structural, morphological, electrical and optic properties are discussed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Epitaxial strain energy measurements of GaN on sapphire by Raman spectroscopyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005H. J. Park Abstract This study reports a non-destructive method of measuring the residual strain in the GaN epilayer grown on sapphire substrate by micro-Raman spectroscopy. Operating in confocal mode this method allows a depth-dependent measurement of residual strain in the epitaxial layer without prior treatment of the sample. This approach to measurement of residual strain is demonstrated on GaN epitaxial films grown by both MOCVD and H-MOVPE. In the case of MOCVD grown films, the biaxial strain energy was found to vary from 0 (GaN surface) to 5.0 kJ/mole (GaN/sapphire interface), but in the case of H-MOVPE grown samples the strain energy varied from 6.5 kJ/mole , hydrostatic strain (GaN surface) to 25.0 kJ/mole , biaxial strain (GaN/sapphire interface), indicating that the surface layer of the N-terminated H-MOVPE material is not free from strain. Estimates are given for the curvature of substrate, lattice parameter of epitaxial layer, and the interface shear modulus. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Schottky diodes fabricated on cracked GaN epitaxial layer grown on (111) siliconPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005Sung-Jong Park Abstract The planar Schottky diodes were fabricated, characterized and modelled to study the electrical characteristics of cracked GaN epitaxial layer on (111) silicon substrate. We deposited Ti/Al/Ni/Au as the ohmic metal and Pt as the Schottky metal. The ohmic contact resistivity was 5.51 × 10,5 ,·cm2 after annealing in N2 ambient at 700 °C for 30 s. The fabricated Schottky diode exhibited the barrier height of 0.7 eV and the ideal factor was 2.4. We got the cutoff wavelength at 360 nm, peak responsivity of 0.097 A/W at 300 nm, and UV/visible rejection ratio was about 104. The SPICE simulation with the circuit model, which was composed with one Pt/GaN diode and three parasitic diodes, showed good agreement with the experiment. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] GaN on Si substrates for LED and LD applicationsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2004Suzuka Nishimura Abstract GaN epitaxial layer has been grown on 2 inch diameter Si substrates by using highly conductive BP buffer crystal. It has been found that the 2-inch GaN on BP/Si wafers are remarkably flat after epitaxial process. BP layer has grown flat and continuously on a large size silicon wafer. GaN has been found to grow continuously on such a substrate.?BP crystals have been found to be highly conductive and controllable depending on the gas ratio. In addition, UV illumination enables us to study the chamber conditions such as contamination by impurity. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] 3C-SiC:Ge alloys grown on Si (111) substrates by SSMBEPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2004P. Weih Abstract In this work for the first time a comprehensive research of (Si1-xC1-y)Gex+y thin films epitaxially grown on Si (111) substrates by solid source molecular beam epitaxy are presented. The layers were grown at substrate temperatures ranging from 900 °C to 1040 °C with a growth rate of 0.6 nm/min. They were analysed by atomic force microscopy, scanning electron microscopy, X-ray diffraction, Auger electron spectroscopy, secondary ion mass spectroscopy and transmission electron microscopy. The structural analysis revealed that the grown epitaxial layer consists of the cubic polytype. A maximum Ge incorporation of 0.16% was achieved in epitaxial layers grown at 900 °C. It was obtained that the Ge concentration decreases with increasing growth temperature. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Solid C60 layer growth on AlN (0001) surface for C60 FET structure by MBEPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003D. Yokoyama Abstract One of the most important problems is how to form an excellent interface between the insulator and the C60 layers in the C60 field-effect doping technique. In this paper, we propose a new structure of the C60 field-effect transistor which consists of an epitaxial AlN layer as the insulator and a C60 epitaxial layer grown on an AlN (0001) surface. We have mainly investigated solid C60 growth on the AlN (0001) surface by the MBE technique in the present work. C60 grains with face centred cubic structure have been obtained on a smooth AlN surface. Four types of the C60 grains were obtained, that is, the 0° orientation and its twin grains and the 30° orientation and its twin grains. We have found that the 0° orientation grains only can be obtained by controlling the growth temperature. The results strongly indicate that an excellent interface between the AlN insulator and the C60 layer can be formed for device applications. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Metalorganic Chemical Vapor Deposition Growth of a GaN Epilayer on an Annealed GaN Buffer LayerPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2003F. Degave Abstract We investigated the growth of an epitaxial layer deposited on an annealed buffer layer using transmission electron microscopy. It is shown that crystalline quality of the epitaxial layer depends on the annealing conditions of the buffer layer. Dislocations and formation of V-shaped defects are observed and may originate from the structure and morphology of the buffer layer. [source] Chemically Directed Assembling of Functionalized Luminescent Nanocrystals onto Plasma Modified Substrates Towards Sensing and Optoelectronic ApplicationsPLASMA PROCESSES AND POLYMERS, Issue S1 2009Eloisa Sardella Abstract In this work semiconductor nanocrystals (NCs) were assembled by means of a layer-by-layer procedure, by properly combining RF (13.56,MHz) glow discharge-assisted processes with wet chemistry approaches. Colloidal core shell type NCs formed by CdSe coated with an epitaxial layer of ZnS (CdSe@ZnS) were then assembled, from aqueous solution, onto the plasma modified materials. The obtained results show that spatially resolved NC assembling can be successfully achieved on micro-structured domains obtained by means of plasma assisted processes. Layers of functionalized NCs are thus demonstrated to be materials that can be effectively integrated into devices for application in photovoltaics, electronic nano-devices and biological sensors. [source] Simulation and implementation of a porous silicon reflector for epitaxial silicon solar cellsPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 5 2008Filip Duerinckx Abstract One of the main challenges in the ongoing development of thin film crystalline silicon solar cells on a supporting silicon substrate is the implementation of a long-wavelength reflector at the interface between the epitaxial layer and the substrate. IMEC has developed such a reflector based on electrochemical anodization of silicon to create a multi-layer porous silicon stack with alternating high and low porosity layers. This innovation results in a 1,2% absolute increase in efficiency for screenprinted epitaxial cells with a record of 13·8%. To reach a better understanding of the reflector and to aid in its continued optimization, several extensive optical simulations have been performed using an in-house-developed optical software programme. This software is written as a Microsoft Excel workbook to make use of its user-friendliness and modular structure. It can handle up to 15 individual dielectric layers and is used to determine the influence of the number and the sequence of the layers on the internal reflection. A sensitivity analysis is also presented. A study of the angle at which the light strikes the reflector shows separate regions in the physical working of the reflector which include a region where the Bragg effect is dominant as well as a region where total internal reflection plays the largest role. The existence of these regions is proved using reflection measurements. Based on these findings, an estimate is made for the achievable current gain with an ideal reflector and the potential of epitaxial silicon solar cells is determined. Copyright © 2008 John Wiley & Sons, Ltd. [source] Large-area epitaxial silicon solar cells based on industrial screen-printing processesPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 8 2005Filip Duerinckx Abstract Thin-film epitaxial silicon solar cells are an attractive future alternative for bulk silicon solar cells incorporating many of the process advantages of the latter, but on a potentially cheap substrate. Several challenges have to be tackled before this potential can be successfully exploited on a large scale. This paper describes the points of interest and how IMEC aims to solve them. It presents a new step forward towards our final objective: the development of an industrial cell process based on screen-printing for >,15% efficient epitaxial silicon solar cells on a low-cost substrate. Included in the discussion are the substrates onto which the epitaxial deposition is done and how work is progressing in several research institutes and universities on the topic of a high-throughput epitaxial reactor. The industrial screen-printing process sequence developed at IMEC for these epitaxial silicon solar cells is presented, with emphasis on plasma texturing and improvement of the quality of the epitaxial layer. Efficiencies between 12 and 13% are presented for large-area (98,cm2) epitaxial layers on highly doped UMG-Si, off-spec and reclaim material. Finally, the need for an internal reflection scheme is explained. A realistically achievable internal reflection at the epi/substrate interface of 70% will result in a calculated increase of 3,mA/cm2 in short-circuit current. An interfacial stack of porous silicon layers (Bragg reflectors) is chosen as a promising candidate and the challenges facing its incorporation between the epitaxial layer and the substrate are presented. Experimental work on this topic is reported and concentrates on the extraction of the internal reflection at the epi/substrate interface from reflectance measurements. Initial results show an internal reflectance between 30 and 60% with a four-layer porous silicon stack. Resistance measurements for majority carrier flow through these porous silicon stacks are also included and show that no resistance increase is measurable for stacks up to four layers. Copyright © 2005 John Wiley & Sons, Ltd. [source] High-rate deposition of epitaxial layers for efficient low-temperature thin film epitaxial silicon solar cellsPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 5 2001Lars Oberbeck Low,temperature deposition of Si for thin-film solar cells has previously been hampered by low deposition rates and low material quality, usually reflected by a low open-circuit voltage of these solar cells. In contrast, ion-assisted deposition produces Si films with a minority-carrier diffusion length of 40,,m, obtained at a record deposition rate of 0.8,,m/min and a deposition temperature of 650°C with a prebake at 810°C. A thin-film Si solar cell with a 20-,m-thick epitaxial layer achieves an open-circuit voltage of 622,mV and a conversion efficiency of 12.7% without any light trapping structures and without high-temperature solar cell process steps. Copyright © 2001 John Wiley & Sons, Ltd. [source] 4H SiC Epitaxial Growth with Chlorine AdditionCHEMICAL VAPOR DEPOSITION, Issue 8-9 2006F. La Abstract The growth rate of a 4H-SiC epitaxial layer has been increased by a factor of 19 (up to 112,,m h,1) with respect to the standard process, with the introduction of HCl in the deposition chamber. The epitaxial layers grown with the addition of HCl has been characterized by electrical, optical, and structural characterization methods. The effects of various deposition parameters on the epitaxial growth process have been described, and an explanation of this behavior in terms of the diffusion coefficient on the surface, Ds, and the ratio between the characteristic times, ,D:,G, has been provided. The diodes, manufactured on the epitaxial layer grown with the addition of HCl at 1600,°C, have electrical characteristics comparable with the standard epitaxial process. This process is very promising for high-power devices with a breakdown voltage of 10,kV. [source] The impact of SiC substrate treatment on the heteroepitaxial growth of GaN by plasma assisted MBECRYSTAL RESEARCH AND TECHNOLOGY, Issue 10-11 2005A. S. Brown Abstract We report on the impact of the preparation of the Si-face 4H-SiC(0001)Si substrate using a Ga flash-off process on the epitaxial growth of GaN by plasma-assisted molecular beam epitaxy. The nucleation, as well as the resultant structural and morphological properties of GaN grown directly on 4H-SiC(0001)Si are strongly influenced by the chemical and morphological modifications of the SiC surface induced by the Ga flash-off process. Herein we describe the impact of the specific concentration of Ga incident on the surface (quantified in terms of monolayer (ML) coverage): of 0.5 ML, 1ML and 2ML. The residual oxygen at the SiC surface, unintentional SiC nitridation and the formation of cubic GaN grains during the initial nucleation stage, are all reduced when a 2 ML Ga flash is used. All of the above factors result in structural improvement of the GaN epitaxial layers. The correlation between the SiC surface modification, the initial nucleation stage, and the GaN epitaxial layer structural quality has been articulated using x-ray photoelectron spectroscopy, x-ray diffraction, atomic force microscopy and spectroscopic ellipsometry data. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] High temperature arsenic doping of CdHgTe epitaxial layersCRYSTAL RESEARCH AND TECHNOLOGY, Issue 1 2004A. Vlasov Abstract Experimental results on solid-state arsenic doping of the n-type bulk and ISOVPE epitaxial CdXHg1- XTe (X = 0.19 ÷ 0.3) alloys are presented. The arsenic doped thin epitaxial CdxHg1- xTe films (nAs , 5 · 1016 ÷ 1 · 1020 cm -3; d = 2 ÷ 5 ,m) obtained by RF sputtering in a mercury glow discharge were used as As diffusion sources. The arsenic diffusion and activation were carried out at temperatures T = 500 ÷ 600 °C under Hg vapour pressure. Immediately after the high temperature treatment all samples were annealed to annihilate point defects. The SIMS analysis was used for determination of the quantitative admixture distribution of As in the diffusion area. The arsenic electrical activity has been evaluated by means of differential Hall, resistivity and thermoemf measurements. The analysis of experimental data obtained as well as their comparison with previously obtained results has been performed. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A new method for analysing peak broadening caused by compositional fluctuation in X-ray diffraction measurementsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2001Kiichi Nakashima A new method for analysing X-ray peak broadening caused by compositional fluctuation is proposed. The method is applicable to epitaxial layers with diamond or zinc-blende structure on (001) substrates. In the new method, a rescaling procedure with a difference variable ,A is applied to measured X-ray profiles and the dependence of the profiles on various reflection indices hkl is analysed. The theoretical formula reveals that X-ray peak profiles become independent of hkl after the rescaling. A new criterion is proposed; an experimental examination based on the criterion makes it possible simply to judge whether or not X-ray peak broadening is caused by compositional fluctuation. The method is verified experimentally and demonstrated by applying it to an InGaAs multilayer sample having artificial compositional fluctuation. [source] Formation of nanovoids/microcracks in high dose hydrogen implanted AlNPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2008R. Singh Abstract Aluminium nitride (AlN) epitaxial layers grown on sapphire were implanted with 100 keV hydrogen, H2+ ions with doses in the range of 5 × 1016 cm,2 to 2.5 × 1017 cm,2 and subsequently annealed at temperatures up to 800 °C in order to observe the formation of surface blisters. The implantation-induced damage in AlN was analyzed by cross-sectional transmission electron microscopy, which revealed a band of defects extending from 330,550 nm from the surface of AlN. Higher magnification TEM images showed the formation of nanovoids that are distributed in the damage band. Upon annealing these nanovoids agglomerate leading to the formation of microcracks. Due to the overpressure of hydrogen trapped in the microcracks, surface blisters are eventually formed in the hydrogen implanted AlN. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Strong ultraviolet emission from non-polar AlGaN/GaN quantum wells grown over r -plane sapphire substratesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003W. H. Sun Abstract GaN and GaN/Al0.25Ga0.75N multiple quantum wells (MQWs) over c - and r -plane sapphire substrates have been grown by metal-organic chemical vapor deposition. A comparative study of photoluminescence (PL) in GaN epitaxial layers and AlGaN/GaN MQWs on these two types of substrates is reported. At low excitation levels, the measured room temperature PL signal in GaN layers grown over r -plane sapphire was more than order of magnitude lower than in GaN on c -plane substrates. In contrast, the emission intensity from AlGaN/GaN MQWs grown over r -plane substrates was almost 30 times stronger than in the structures grown over c -plane sapphire. Furthermore, with excitation power density up to 1 MW/cm2, the PL peak position for the non-polar MQWs kept completely stable whereas the one for the c -plane structures exhibited a blue shift as large as 250 meV. We attribute this large difference in the ultraviolet emission intensity to the suppression of a strong quantum Stark effect in the AlGaN/GaN MQWs on the r -plane sapphire. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Hybrid reflections in InGaP/GaAs(001) by synchrotron radiation multiple diffractionPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2009Alan S. de Menezes Abstract Hybrid reflections (HRs) involving substrate and layer planes (SL type) [Morelhão et al., Appl. Phys. Lett. 73 (15), 2194 (1998)] observed in Chemical Beam Epitaxy (CBE) grown InGaP/GaAs(001) structures were used as a three-dimensional probe to analyze structural properties of epitaxial layers. A set of (002) rocking curves (, -scan) measured for each 15° in the azimuthal plane was arranged in a pole diagram in , for two samples with different layer thicknesses (#A , 58 nm and #B , 370 nm) and this allowed us to infer the azimuthal epilayer homogeneity in both samples. Also, it was shown the occurrence of (13) HR detected even in the thinner layer sample. Mappings of the HR diffraction condition (,:,) allowed to observe the crystal truncation rod through the elongation of HR shape along the substrate secondary reflection streak which can indicate in-plane match of layer/ substrate lattice parameters. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Exciton localization in MgxZnyCd1,x,ySe alloyPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2004O. Maksimov Abstract We report photoluminescence and reflectivity measurements of MgxZnyCd1,x,ySe epitaxial layers (0 < x < 0.53) grown by molecular beam epitaxy on InP (100) substrates. Significant emission line broadening, increase in activation energy and Stokes shift are monitored with increasing Mg content. For MgxCdyZn1,x,ySe samples with large Mg content (x > 0.3), we observe an anomalous temperature dependence of both the emission energy and line broadening. This behavior is assigned to the emission from localized states. Different mechanisms of carrier localization are discussed and exciton localization on statistical CdSe clusters is proposed to be the most likely one. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Localized biexcitons in AlxGa1,xN ternary alloy epitaxial layersPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003Y. Yamada Abstract Excitonic optical properties of AlxGa1,xN ternary alloy epitaxial layers have been studied by means of photoluminescence (PL), time-resolved PL, and PL excitation (PLE) spectroscopy. The luminescence line due to radiative recombination of biexcitons was clearly observed in an Al0.08Ga0.92N epitaxial layer. The PL decay time of excitons and biexcitons was estimated to be 350 and 210 ps, respectively. PLE spectroscopy of biexcitons enabled us to observe a two-photon absorption process of biexcitons. On the basis of the energy separation between exciton resonance and two-photon biexciton resonance, the binding energy of biexcitons in Al0.08Ga0.92N was estimated to be 15 ± 2 meV. This value was approximately 2.5 times as large as the binding energy of biexcitons in GaN. This value was also found to be comparable to the observed energy separation between the exciton luminescence and the biexciton luminescence, which indicated the strong localization of biexcitons. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Exciton localization in Al-rich AlGaN ternary alloy epitaxial layersPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010Hideaki Murotani Abstract Exciton localization in Al-rich AlGaN ternary alloy epitaxial layers has been studied by means of temperature-dependent photoluminescence (PL) spectroscopy. Anomalous temperature dependence of the PL peak energy (red-blue shift) was observed, which enabled us to estimate the localization energy of excitons. The localization energy increased as the 1.2th power of the exciton linewidth. The value of exponent for Al-rich alloys was smaller than that for Ga-rich alloys. This indicated that the excitons in Al-rich alloys were strongly localized compared to that in Ga-rich alloys. In addition, the exponent value for Al-rich alloys increased with increasing excitation power density. This increase in the exponent suggested that the exciton population approached the extended states owing to the saturation of localized states by photo-generated excess excitons. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] RF-MBE growth of InN on 4H-SiC (0001) with off-anglesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010Misao Orihara Abstract We have grown InN on 4H-SiC (0001) substrates with various off-angles by RF-N2 plasma molecular beam epitaxy (RF-MBE). Scanning electron microscope observation revealed that InN films grown on 4H-SiC (0001) substrates with off-angles of 4° and 8° are very smooth and that there are no voids which have often observed for InN epitaxial layers. X-ray diffraction reciprocal space maps for InN grown on 4H-SiC (0001) showed that the c-axes of InN grown on 4H-SiC 4° and 8° off substrates are inclined by 0.35° and 0.8°, respectively, toward the misorientation of the substrate while the c-axis of InN is parallel to that of 4H-SiC for the on-axis substrate. Strong PL peak was observed from InN grown on 4° off substrate at 0.68 eV at 15 K. The PL peak was clearly observed even at room temperature and simply shifted to lower energies with increasing temperature. The difference in the PL peak energy between at 15 K and 300 K was 20 meV, which is reasonable taking into account the difference in the thermal coefficients of InN and SiC (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Total reflectance and Raman studies in AlyInxGa1-x-yN epitaxial layersPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2010A. Margarida Bola Abstract This study comprises a set of AlyInxGa1-x-yN thin films grown on GaN/sapphire substrate by MOVPE, with In content between 2 and 8% and Al between 21 and 38%. The thin films were optically characterized by means of UV-Visible total reflectance and ,-UV-Raman scattering, performed at room temperature. It is shown that the [Al]/[In] ration influences strongly the Reflectance spectra and a good correlation has been found between the reflectance maximum located at higher energy and the band gap predicted by Vegard's law for quaternary alloys. The Raman results indicate that the LO-AlGaN-like vibration mode is the dominated vibration in good agreement with the oscillator strength values obtained theoretically [12] for this alloys. It is shown how the influence of competing effects, such as composition and strain influences the frequency observed for the LO-AlGaN-like mode (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Low-temperature MBE-grown GaBiAs layers for terahertz optoelectronic applicationsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2009Vaidas Pa, ebutas Abstract Gallium bismide arsenide epitaxial layers were grown by molecular-beam-epitaxy at low substrate temperatures and investigated for their suitability in terahertz optoelectronic applications. Optical pump-terahertz probe measurements on these layers have shown that carrier dynamics can be described using two characteristic times. The faster decay component has characteristic times shorter than 1 ps, whereas the slower component decays in several tens of picoseconds. Fitting the electron lifetimes dependence on optical excitation level the electron trapping cross-section and trap density were determined. The possible mechanism of carrier recombination was discussed. The photoconductive terahertz emitters and detectors made from GaBiAs layers have been manufactured and used in time-domain spectroscopy system with a signal bandwidth larger than 4.5 THz. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||