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Epilayers
Kinds of Epilayers Selected AbstractsMetalorganic 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] Nitrogen-doped zirconia single crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2006T.-C. Rödel Abstract The aim of this work is the preparation of nitrogen-doped single crystals of cation-stabilized zirconia. Thin plates of these crystals were nitrided in a graphite heated resistance furnace with nitrogen as reaction gas. Several dwell times and reaction temperatures were tested and their effect on the amount of incorporated nitrogen is investigated. During nitridation at high temperatures a rock salt-type ,ZrN' layer grows on the surface, leading to the destruction of the crystal. In contrast to the fluorite-type bulk material, which can be described as a fast anion conductor, the surface layer shows electronic conductivity. For possible applications of the bulk material (solid electrolyte) the formation of the surface layer must be avoided. Therefore, the interface between surface epilayer and bulk material was investigated in detail by electron microscopy methods. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Nanoshells with Targeted Simultaneous Enhancement of Magnetic and Optical Imaging and Photothermal Therapeutic ResponseADVANCED FUNCTIONAL MATERIALS, Issue 24 2009Rizia Bardhan Abstract Integrating multiple functionalities into individual nanoscale complexes is of tremendous importance in biomedicine, expanding the capabilities of nanoscale structures to perform multiple parallel tasks. Here, the ability to enhance two different imaging technologies simultaneously,fluorescence optical imaging and magnetic resonance imaging,with antibody targeting and photothermal therapeutic actuation is combined all within the same nanoshell-based complex. The nanocomplexes are constructed by coating a gold nanoshell with a silica epilayer doped with Fe3O4 and the fluorophore ICG, which results in a high T2 relaxivity (390,mM,1,s,1) and 45× fluorescence enhancement of ICG. Bioconjugate nanocomplexes target HER2+ cells and induce photothermal cell death upon near-IR illumination. [source] Controlled Growth of High-Quality ZnO-Based Films and Fabrication of Visible-Blind and Solar-Blind Ultra-Violet DetectorsADVANCED MATERIALS, Issue 45 2009Xiaolong Du Abstract ZnO is a wide-bandgap (3.37,eV at room temperature) oxide semiconductor that is attractive for its great potential in short-wavelength optoelectronic devices, in which high quality films and heterostructures are essential for high performance. In this study, controlled growth of ZnO-based thin films and heterostructures by molecular beam epitaxy (MBE) is demonstrated on different substrates with emphasis on interface engineering. It is revealed that ultrathin AlN or MgO interfacial layers play a key role in establishing structural and chemical compatibility between ZnO and substrates. Furthermore, a quasi-homo buffer is introduced prior to growth of a wurtzite MgZnO epilayer to suppress the phase segregation of rock-salt MgO, achieving wide-range bandgap tuning from 3.3 to 4.55,eV. Finally, a visible-blind UV detector exploiting a double heterojunction of n-ZnO/insulator-MgO/p-Si and a solar-blind UV detector using MgZnO as an active layer are fabricated by using the growth techniques discussed here. [source] Enhancement of crystalline perfection by organic dopants in ZTS, ADP and KHP crystals as investigated by high-resolution XRD and SEMJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2006S. Parthiban To reveal the influence of complexing agents on crystalline perfection, tristhiourea zinc(II) sulfate (ZTS), ammonium dihydrogen phosphate (ADP) and potassium hydrogen phthalate (KHP) crystals grown by slow-evaporation solution growth technique using low concentrations (5 × 10,3M) of dopants like ethylenediamminetetraacetic acid (EDTA) and 1,10-phenanthroline (phen) were characterized by high-resolution X-ray diffractometry (XRD) and scanning electron microscopy (SEM). High-resolution diffraction curves (DCs) recorded for ZTS and ADP crystals doped with EDTA show that the specimen contains an epilayer, as observed by the additional peak in the DC, whereas undoped specimens do not have such additional peaks. On etching the surface layer, the additional peak due to the epilayer disappears and a very sharp DC is obtained, with full width at half-maximum (FWHM) of less than 10,arcsec, as expected from the plane wave dynamical theory of X-ray diffraction for an ideally perfect crystal. SEM micrographs also confirm the existence of an epilayer in doped specimens. The ZTS specimen has a layer with a rough surface morphology, having randomly oriented needles, whereas the ADP specimen contains a layer with dendric structure. In contrast to ADP and ZTS crystals, the DC of phen-doped KHP shows no additional peak, but it is quite broad (FWHM = 28,arcsec) with a high value of integrated intensity, , (area under the DC). The broadness of the DC and the high value of , indicate the formation of a mosaic layer on the surface of the crystal. However, similar to ADP and ZTS, the DC recorded after etching the surface layer of the KHP specimen shows a very sharp peak with an FWHM of 8 arcsec. An SEM photograph of phen-doped KHP shows deep cracks on the surface, confirming the mosaicity. After removing the surface layer, the SEM pictures reveal a smooth surface. A similar trend is observed with other complexing agents, like oxalic acid, bipy and picolinic acid. However, only typical examples are described in the present article where the effects were observed prominently. The investigations on ZTS, ADP and KHP crystals, employing high-resolution XRD and SEM studies, revealed that some organic dopants added to the solution during the growth lead to the formation of a surface layer, due to complexation of these dopants with the trace metal ion impurities present in the solution, which prevents the entry of impurities, including the solvent, into the crystal, thereby assisting crystal growth with high crystalline perfection. The influence of organic dopants on the second harmonic generation efficiency is also investigated. [source] Combined 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] Growth behavior and microstructure of ZnO epilayer on ,-LiAlO2(100) substrate by chemical vapor depositionPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2009Liuwen Chang Abstract Low lattice-mismatched ,-LiAlO2(100) substrates were employed to grow ZnO epitaxial films by chemical vapor deposition. The influence of growth temperature on growth behavior of ZnO was investigated. Results indicated that the low lattice-matched (100) crystallites nucleate on substrate at all growth temperatures employed. However, a second type of crystallites having an (0001) orientation can also nucleate on substrate at low growth temperature of 575 °C and 640 °C. The growth rate of the later crystallite is, however, higher than that of the (100) one and finally results in a single crystalline ZnO film having an [0001] azimuthal orientation. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Bismuth containing III,V quaternary alloy InGaAsBi grown by MBEPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2006G. Feng Abstract InGaAsBi epilayers were created on InP substrates by molecular beam epitaxy for the first time. The high crystalline quality of the InGaAsBi epilayer with smooth interface was confirmed by high resolution X-ray diffraction measurements. Up to 2.5% Bi was incorporated in the film based on Rutherford back scattering (RBS) results. The RBS channeling spectra give clear evidence that the Bi atoms were substitutionally located in the InGaAs zinc-blende lattice sites. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] AlGaN/GaN HFETs on Fe-doped GaN substratesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010Yoshinori Oshimura Abstract AlGaN/GaN HFETs with different undoped GaN thicknesses were grown on Fe-doped freestanding GaN substrates by conventional MOVPE. To realize a high drain current, thick undoped GaN is found to be necessary. SIMS measurement shows that Fe is redistributed into the epilayer, by which the scattering center is generated at the channel when the thickness of the undoped GaN is insufficient. We also observed a similar Fe profile in the GaN/sapphire template placed on the side of the Fe-doped GaN substrate during growth. Therefore, Fe in the Fe-doped GaN substrate is redistributed not only through a solid but also through vapor. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structural and optical characterization of (11-22) semipolar GaN on m -plane sapphire without low temperature buffer layerPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010Sung-Nam Lee Abstract We reported the high quality semipolar (11-22) GaN grown on m-sapphire by using the novel two-step growth method without low temperature GaN or AlN buffer layer. It is found that macroscopic surface morphology of semipolar GaN epilayer was very smooth, while microscopic surface structure was arrowhead-like surface structure toward the direction of [1-21-1]. Anisotropic crystal properties of semipolar GaN/m-sapphire were also observed by two incident directions of X-ray beam. Therefore, we suggested that the anisotropic crystal properties and arrow-head like surface structure would be caused by heteroepitaxial crystallograhpic difference between semipolar GaN and m-sapphire. Additionally, photoluminescence (PL) measurements showed the strong bandedge emission of n-type semipolar GaN without yellow luminescence (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Characteristics of He+ -irradiated Ni Schottky diodes based on 4H-SiC epilayer grown by sublimationPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2009A. M. Strel'chuk Abstract Forward and reverse current-voltage (I-V) and capacitance-voltage (C-V) characteristics of the of He+ , irradiated Ni-SiC(4H) Schottky diodes (SDs) are presented prior and after irradiation. The effect of irradiation was weakly observed in the region of small forward and reverse current, but series resistance of SD demonstrated tendency to rise with increasing irradiation dose. The most interesting effect was the big scatter of the series resistances after exposure to high irradiation dose 2×1012 cm -2. By contrast, uncompensated donor concentration had just minor changes (from 3.3×1017 cm -3 prior irradiation to 1.8×1017 cm -3 at highest irradiation dose) with no connection with SDs resistance. Hypothesis that localized defect-induced current paths could explain this behaviour is discussed. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] GaN/air gap based micro-opto-electro-mechanical (MOEM) Fabry-Pérot filtersPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007E. Cho Abstract Structural and optical properties of Fabry-Pérot filters (FPFs) with GaN/air gap based distributed Bragg reflectors (DBRs) were studied. Reflectance of GaN/air gap DBRs on sapphire substrate was calculated from the standard transmission matrix method and results showed that 98% reflectance is achievable with only 3.5 pairs at a center wavelength of 450 nm. The thickness of the GaN layer and the first AlN layer was determined according to the deformation induced by the residual stress. In-plane strain corresponding to growth conditions and the thickness of the GaN epilayer was considered for this analysis. Optical tuning efficiency and spectral range were found to be 0.27 and 25 nm respectively for FPFs with GaN/air gap (322 nm/113 nm) based DBRs and a ,0/2 air resonant cavity. The calculated pull-in voltage was 1.5 V. Crack free AlN grown on GaN by in-house MOCVD showed an etching rate of 0.2 nm/min. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] 1.3 µm high indium content (42.5%) GaInNAs/GaAs quantum wells grown by molecular beam epitaxyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2006Zhichuan Niu Abstract High structural and optical quality 1.3 µm GaInNAs /GaAs quantum well (QW) samples with 42.5% indium content were successfully grown by molecular beam epitaxy. The growth of well layers was monitored by reflection high-energy electron diffraction (RHEED). Room temperature photoluminescence (PL) peak intensity of the GaIn0.425NAs/GaAs (6 nm/20 nm) 3QW is higher than, and the full width at half maximum (FWHM) is comparable to, that of In0.425GaAs/GaAs 3QW, indicating improved optical quality due to strain compensation effects by introducing N to the high indium content InGaAs epilayer. The measured (004) X-ray rocking curve shows clear satellite peaks and Pendellösung fringes, suggesting high film uniformity and smooth interfaces. The cross sectional TEM measurements further reveal that there are no structural defects in such high indium content QWs. (© 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] Growth of InGaN quantum dots on GaN by MOVPE, employing a growth temperature nitrogen annealPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003R. A. Oliver Abstract We have studied the growth of InGaN epitaxial layers on GaN by MOVPE (metal-organic vapour phase epitaxy), and have discovered that nanostructures may be formed if a flat epilayer is annealed in molecular nitrogen immediately after growth. The size and density of the nanostructures are shown to be dependent on the growth/anneal temperature. We demonstrated the quantum dot nature of our nanostructures by performing spatially resolved photoluminescence on samples that had been capped with a layer of GaN, grown at the same temperature as the InGaN epilayer. This revealed narrow, delta-function-like lines in the luminescence spectrum with full width at half maximum (FWHM) limited by the resolution of the spectrometer at 4.2 K. Measurement of the FWHM as a function of temperature revealed significant broadening above 20 K. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Improved crystallinity and polarity manipulation of MOVPE-grown GaN epilayers with deep sapphire-nitridation followed by Al-preflow at high temperaturesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003B. W. Seo Abstract The polarity manipulation and crystallinity of GaN epilayers grown by metalorganic vapor phase epitaxy (MOVPE) on deeply nitrided c -sapphire was studied by using TMAl preflow at high temperatures (HT-TMAl preflow) of 1100 °C. It was found that the HT-TMAl preflow was very effective to change the surface polarity; the successful change to Ga-polarity from N-polarity and the atomic-steps were observed when the Al layer thickness was above two-monolayers, though it was remained N-polarity without the Al layer. The crystallinity of GaN epilayer is increased using HT-TMAl preflow. High quality Ga-polarity GaN epilayers was grown by this technique and typical full width at half maximums (FWHMs) for X-ray rocking curves were 300,320 arcsec and 450,480 arcsec for (002) and (102) diffractions, respectively. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Formation of "air-gap" structure at a GaN epilayer/substrate interface by using an InN interlayerPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003A. Yamamoto Abstract We propose a new technique for "air-gap" formation at a GaN/sapphire interface by using an InN interlayer. This is aimed to grow epitaxial GaN films with reduced stress and cracks. First, an InN interlayer of about 0.2 ,m thick is grown at 600 °C in atmospheric pressure. Then a 30 nm-thick GaN buffer layer is grown on the InN layer at 550 °C. The substrate temperature is ramped up to 1000 °C in the NH3 flow, and finally a 1.5 ,m-thick GaN epilayer is grown on the annealed GaN buffer layer using nitrogen carrier gas. Consequently, an "air-gap" structure is naturally formed close to the substrate surface. During the ramping period of substrate temperature, the InN layer decomposes due to its thermal instability and metallic In is formed. It is found that metallic In drops as a result of InN decomposition contribute to the air-gap formation. No cracks are found on the GaN surface and a reduced stress in the layer is confirmed by PL and Raman shift measurements. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spatially resolved X-ray diffraction as a tool for strain analysis in laterally modulated epitaxial structuresCRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2009A. Wierzbicka Abstract Spatially resolved X-ray diffraction (SRXRD) is applied for micro-imaging of strain in laterally modulated epitaxial structures. In GaAs layers grown by liquid phase epitaxial lateral overgrowth (ELO) on SiO2 -masked GaAs substrates a downward tilt of ELO wings caused by their interaction with the mask is observed. The distribution of the tilt magnitude across the wings width is determined with ,m-scale spatial resolution. This allows measuring of the shape of the lattice planes in individual ELO stripes. If a large area of the sample is studied the X-ray imaging provides precise information on the tilt of an individual wing and its distribution. In heteroepitaxial GaSb/GaAs ELO layers local mosaicity in the wing area is found. By the SRXRD the size of microblocks and their relative misorientation were analyzed. Finally, the SRXRD technique was applied to study distribution of localized strain in AlGaN epilayers grown by MOVPE on bulk GaN substrates with AlN mask. X-ray mapping proves that by mask patterning strain in AlGaN layer can be easily engineered, which opens a way to produce thicker, crack-free AlGaN layers with a higher Al content needed in GaN-based laser diodes. All these examples show that high spatial and angular resolutions offered by SRXRD makes the technique a powerful tool to study local lattice distortions in semiconductor microstructures. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Homoepitaxy of ZnTe on (100) oriented substrates: Technology issues and MOVPE growth aspectsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 10-11 2005M. Traversa Abstract The metalorganic vapour phase epitaxy of ZnTe on single crystal (100)ZnTe:P wafers is reported. The technological steps to prepare a substrate surface suitable for the high quality homoepitaxy of ZnTe are identified and optimised in terms of structural and morphological properties of overgrown epilayers. Removal of ,7 µm of material from the ZnTe:P wafers by chemical etching in 1% Br2 -methanol solution proved necessary to achieve a sufficiently smooth and homogeneous surface; in-situ H2 heat treatment of the wafers at 350°C immediately before growth ensures optimal desorption of residual oxides, allowing epilayer crystalline quality comparable to the substrate. However, the structure of epilayers degrades for growth temperatures (TG) above 350 °C due to the occurrence of stacking faults (SFs) within ,200-300 nm from the epilayer-substrate interface. Accordingly, the epilayer band-edge luminescence vanishes below 350 nm, indicating a worsening of the material radiative efficiency in very thin epilayers. The epilayer surface morphology is the result of a complex interplay between SF nucleation and Te:Zn ad-atom stoichiometry during growth. Almost featureless morphologies are obtained for growth at 350 °C, i.e. under nearly stoichiometric surface conditions. Pyramid-like hillocks develop instead for TG , 360 °C, corresponding to Te-rich surface conditions, their density rapidly increasing up to around 9 × 106 cm,2 at TG = 400 °C. Hillocks occur in close pairs on the epilayer surface, their nucleation being strongly reduced if a thin ZnTe buffer layer is grown at low (325 °C) temperature, i.e. if SFs do not occur at the epilayer-substrate interface. This demonstrates that hillocks form as a result of three-dimensional growth around partial dislocations pairs bounding SFs, the phenomenon being driven by Te ad-atoms experiencing a Schwoebel potential barrier at the surface step edges around the dislocations. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Routes to Grow Well-Aligned Arrays of ZnSe Nanowires and Nanorods,ADVANCED MATERIALS, Issue 11 2005X. Zhang Well-aligned ZnSe nanowires and nanorods can be grown on ZnSe epilayers on different GaAs substrates, with and without catalyst, by metal,organic chemical vapor deposition. Gold particles affect the number density, growth direction, and the morphology of the resulting nanostructures. In the absence of the gold catalyst, hexagonal nanorods grow along the <111> directions (see Figure). Growth defects on the epilayers may be the nucleation sites of the nanorods. [source] MOVPE growth and characterization of a -plane AlGaN over the entire composition rangePHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 7 2010Masihhur R. Laskar Abstract We report the metal organic vapor phase epitaxy (MOVPE) growth and characterization of non-polar (110) a -plane Alx Ga1,xN on (102) r -plane sapphire substrates over the entire composition range. Alx Ga1,xN samples with ,0.8 ,m thick layers and with x = 0, 0.18, 0.38, 0.46, 0.66, and 1.0 have been grown on r -plane sapphire substrates. The layer quality can be improved by using a 3-stage AlN nucleation layer and appropriate V/III ratio switching following nucleation. All a -plane AlGaN epilayers show an anisotropic in-plane mosaicity, strongly influenced by Al incorporation and growth conditions. Careful lattice parameter measurements show anisotropic in-plane strain that results in an orthorhombic distortion of the hexagonal unit cell, making Al composition determination from X-ray diffraction difficult. In general lower Al incorporation is seen in a -plane epilayers compared to c -plane samples grown under the same conditions. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] In-plane polarization of GaN-based heterostructures with arbitrary crystal orientationPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 10 2010Q. Y. Wei Abstract The total polarization fields of pseudomorphic InxGa1,xN/GaN and AlxGa1,xN/GaN heterostructures with 0,,,x,,,0.4 have been calculated as a function of the crystal orientation. Especial attention is placed on the direction and magnitude of in-plane piezoelectric polarization, which is not negligible for the non-polar and semi-polar growth. For an arbitrary crystal orientation, the piezoelectric polarization prevails in the InGaN/GaN system while the spontaneous polarization prevails in the AlGaN/GaN system. The in-plane potential due to polarization fields in non-polar epilayers is found to depend on the degree of planarity of the heterojunctions, and on the respective lateral dimensions. [source] Excitonic effects and Franz,Keldysh oscillations in photoreflectance of ultrapure GaAs epilayersPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2009O. S. Komkov Abstract A model based on the exciton theory has been presented for lineshape analysis of photoreflectance (PR) spectra. Experimental PR spectra of high-quality thick GaAs epilayers of different purity were measured to verify the theoretical results. It has been shown that excitonic effects completely prevail over the one-electron theory in the formation of photoreflectance spectrum even at high electric fields and room temperature, giving evidence of the existence of Franz,Keldysh oscillations enhanced by excitonic effects. A comparison of PR spectra simulated using the exciton theory and the one-electron approximation has shown that the semiperiods of the oscillations were practically similar. This demonstrates the validity of using the simple "high-field" model of Aspnes and Studna to determine surface electric fields. In photoreflectance of thick ultrapure GaAs epilayers an oscillating structure was experimentally observed in the region between the excitonic and the fundamental bandgap. This provides a possibility for contactless characterization not only for doped (N , 1014,1018 cm,3) but also for ultrapure (N , 1011,1013 cm,3) GaAs epilayers as well as other semiconductor materials. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Hall effect anomalies in n-type Pb1,xEux Se layers grown on siliconPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 10 2007A. Almaggoussi Abstract Transport measurements (resistivity and Hall density) were made in the temperature range 10,300 K on n-Pb1,xEux Se (0 , x , 8%) epilayers grown by molecular beam epitaxy on silicon substrates. In the vicinity of 77 K anomalies of electron concentration were observed. To explain this anomalous behaviour, a model is proposed based on the existence of three levels: two donors and one acceptor. The origin of these levels is attributed to native defects. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optical, structural, and magnetic properties of p-type GaN implanted with Fe+ (5 and 10 at%)PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2007Yoon Shon Abstract p-type GaN epilayers were prepared by metalorganic chemical vapor deposition and subsequently implanted with Fe+. The results of energy dispersive X-ray peak displayed the Fe-injected concentration of 5 and 10 at%, respectively. The results of photoluminescence measurement show that optical transitions related to Fe appear at 2.5 and 3.1 eV. It was confirmed that the photoluminescence peak at 2.5 eV is a donor-Fe acceptor transition and the photoluminescence peak at 3.1 eV is a conduction band-Fe acceptor transition. Apparent ferromagnetic hysteresis loops measured at 10 and 300 K with the Fe concentration of 10 at% were observed, and the temperature-dependent magnetization displayed a ferromagnetic behavior persisting up to 300 K. The systematic enhancement of ferromagnetic hysteresis loops for GaN implanted with high doses of Fe (5 , 10 at%) takes place with an increase in the annealing temperature from 700 to 850 °C. The trends of magnetic properties coincide with the results of the increased full width at half maximum of triple axis diffraction for GaN (0002) including the appearance of GaFeN, the enhanced Fe-related photoluminescence transitions, and the increased sizes of symmetric spin ferromagnetic domains GaFeN in atomic force microscopy and magnetic force microscopy systematically. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Bismuth containing III,V quaternary alloy InGaAsBi grown by MBEPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2006G. Feng Abstract InGaAsBi epilayers were created on InP substrates by molecular beam epitaxy for the first time. The high crystalline quality of the InGaAsBi epilayer with smooth interface was confirmed by high resolution X-ray diffraction measurements. Up to 2.5% Bi was incorporated in the film based on Rutherford back scattering (RBS) results. The RBS channeling spectra give clear evidence that the Bi atoms were substitutionally located in the InGaAs zinc-blende lattice sites. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Mg-doped AlGaN grown on an AlN/sapphire template by metalorganic chemical vapour depositionPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2006Hongbo Yu Abstract The growth of high-performance Mg-doped p-type AlxGa1,xN (x = 0.35) layers using low-pressure metalorganic chemical vapour deposition on an AlN/sapphire template is reported. The influence of growth conditions on the p-type conductivity of the AlxGa1,xN (x = 0.35) alloy was investigated. It was found that the p-type resistivity of the AlGaN alloy demonstrates a marked dependence on the Mg concentration, V/III ratio and group III element flow rate. A minimum p-type resistivity of 3.5 , cm for AlxGa1,xN (x = 0.35) epilayers was achieved. A Ni/Au (10 nm/100 nm) ohmic contact was also fabricated and a specific contact resistivity of 8.1 × 10,2 , cm2 was measured. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Electrical transport phenomena in magnesium-doped p-type GaNPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2009Leszek Konczewicz Abstract In this paper we present the resistivity and Hall-effect measurements on p-type GaN doped with Mg. The experiments were carried out as a function of hydrostatic pressure up to 1200 MPa in the temperature range 260,400 K. Both bulk GaN crystals as well as GaN:Mg epilayers were studied. In the investigated samples the decrease of resistivity and increase of hole concentration under pressure was observed. Such a behavior, which is contrary to the n-type material, strongly suggests a decrease of the ionization energy of Mg acceptor (Ea = 183 meV) with pressure. This shift is very weak, less than ,2 meV/GPa. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Surface morphology effects on the optical phonon modes in InAsxSb1,x epilayers on GaAs(001)PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2006P. Jayavel Abstract We have studied Raman scattering from longitudinal- and transverse-optical (LO and TO) phonon modes in InAsxSb1,x epilayers grown on GaAs(001) substrates with various arsenic compositions (x). InSb-like and InAs-like LO and TO phonon modes of the epilayers are observed. We find that the peak intensity ratio of the InAs-like LO to TO-mode decreases for x < 0.6 while it increases for x > 0.6. This intensity ratio change is attributed to two- and three-dimensional (2D and 3D) growth mode of the epilayers using atomic force microscopy. Further, the intensity ratio depends on the root mean square surface roughness of the alloy. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Magneto-optical spectroscopy of (Zn,Co)O epilayersPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2006W. Pacuski Abstract We present a magneto-optical study of (Zn,Co)O layers grown by molecular beam epitaxy. We observed sharp lines related to 4A2,2E intra-ionic Co2+ transitions, and to the A , B and C excitons. Intra-ionic transitions observed by absorption and photoluminescence were used to determine the values of the parameters describing the isolated Co ions, such as the easy-plane magnetic anisotropy and the g -factor of the S = 3/2 Cobalt spin. Excitonic transitions observed in reflectivity were used to determine the giant Zeeman splitting and to estimate the effective coupling ,N0(, , , ),A ,B = 0.4 eV between excitons and Cobalt spins. Due to the electron,hole exchange within the exciton, this effective spin,exciton coupling is much weaker than the exchange integrals for free carriers, estimated to be N0|, , , | , 0.8 eV, with a positive value of (, , , ) if the normal ordering of the valence band of ZnO is assumed. The Zeeman splitting of diluted samples and the magnetic circular dichroism (for a higher Co content) are proportional to the magnetization of the paramagnetic, isolated Cobalt ions. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||