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Sapphire Substrates (sapphire + substrate)
Kinds of Sapphire Substrates Selected AbstractsOptical properties of InN grown on Si(111) substratePHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2010E. Sakalauskas Abstract A comprehensive characterization of the optical properties of wurtzite InN films grown by molecular beam epitaxy on Si(111) substrates is presented. Two types of films are investigated in this work: InN on AlN/Si(111) and InN on GaN/AlN/Si(111). Their properties are compared to a layer deposited on GaN/sapphire substrate. The dielectric function (DF) is obtained from spectroscopic ellipsometry (SE). The infrared studies yield the plasma frequency and thus the electron density, while the interband absorption is probed between 0.56 and 9.8,eV. For InN grown on Si(111) substrate, the absorption onset is slightly shifted to higher energies with respect to the InN film grown on GaN/sapphire which can be attributed to higher electron concentrations. Despite this, strongly pronounced optical transitions due to critical points of the band structure are found in the high-energy part of the DF. It emphasizes the already promising quality of the InN films on silicon. Band-gap renormalization (BGR), band filling, and strain are taken into account in order to estimate the intrinsic band gap of wurtzite InN. For the InN layers on silicon, we get a band gap between 0.66 and 0.685,eV. [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] Effects of growth temperature on exciton lifetime and structural properties of ZnO films on sapphire substratePHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 15 2006S. Cho Abstract We report on optimization of growth conditions by studying the structural and optical properties of ZnO films grown on sapphire substrate by pulsed laser deposition at different growth temperatures. The crystallographic structure and surface morphology were studied by X-ray diffraction and atomic force microscopy, respectively. The flattest surface was observed in the sample grown at substrate temperature of 500 °C. The optical characterization was performed by steady state and time resolved photoluminescence spectroscopy. Photoluminescence of the samples was studied at low CW excitation and at high-power-density pulsed excitation in picosecond domain. Stimulated emission was observed at pulsed excitation. Carrier lifetimes were found to significantly depend on the growth temperature reaching the peak value also in the samples grown at approximately 500 °C. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Highly a -axis oriented ,-LiAlO2 layer on a -plane sapphire fabricated by vapor transport equilibrationPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2004Shengming Zhou Abstract A single-phase ,-LiAlO2 layer with a highly-preferred (100) orientation on sapphire substrate is successfully fabricated by vapor transport equilibration (VTE) technique in Li-rich ambient. The VTE treatment temperature is essential to obtaining the high-quality layer of ,-LiAlO2, and the optimized temperature is about 1050 °C in the present work. It is promising to fabricate the ,-LIAlO2(100)//sapphire composite substrate for GaN-based epitaxial film. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Activation energy of Mg in a -plane Ga1,xInx N (0 < x < 0.17)PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2009Daisuke Iida Abstract We investigated the electrical properties of Mg-doped Ga1,xInx N grown on an a -plane template. High-hole-concentration p-type Mg-doped Ga1,xInx N films with an InN molar fraction of 0.17 were fabricated on sidewall-epitaxial-lateral overgrown a -plane GaN grown on an r -plane sapphire substrate by MOVPE. Variable-temperature Hall effect measurement showed that a maximum hole concentration of 1.4 × 1019 cm,3 for x = 0.17 was reproducibly achieved at room temperature. The activation energy of Mg acceptors in Mg-doped a -plane Ga0.83In0.17N was found to be as low as 48 meV. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Hot carrier energy losses in conducting layers of AlGaN/GaN heterostructures grown on SiC and Al2O3 substratesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2006B. A. Danilchenko Abstract The energy relaxation rate for hot electrons in AlGaN/GaN heterostructures was measured over the temperature range 4.2,300 K. Samples grown on sapphire and 4H-SiC substrates were studied. The most important result is that the hot carrier energy dissipation differs for samples grown on sapphire and SiC substrates. In the case of sapphire substrate, the dissipation can be described by the emission of optical phonons with an energy of 90 meV and relaxation time of 25 fs. In the case of SiC substrate, both activation energy and relaxation time exceed the values characteristic of the electron-LO-phonon dissipation process. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Photoluminescence from InGaN/GaN MQWs on sapphire and membranes fabricated by laser lift-offPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2004Tongjun Yu Abstract Photoluminescence and Raman scattering spectra of InGaN/GaN MQWs on sapphire and membranes free of substrate fabricated by laser lift-off have been studied. It is observed that photoluminescence peak of 850 °C annealed sample red-shifts from that of as grown sample, while in the case of membrane samples, the luminescence peak blue-shifts when annealed at 700 °C. In Raman scattering spectra, InGaN/GaN MQWs film without sapphire substrate has a lower E2 mode frequency (569.3 cm,1) than that of the films with substrate (570.8 cm,1), which indicates that compressive stress in the films releases partially when the sapphire substrate is taken off. It is believed that the piezoelectric field decrease leads to the blue-shift in luminescence spectra. Compared with the samples with sapphire substrate, the free-standing membranes showed blue-shift of luminescence peak after relatively low temperature annealing, because the piezoelectric field reduced more easily in the films without substrate. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Growth and properties of In-rich InGaN films grown on (0001) sapphire by RF-MBEPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2004M. Kurouchi Abstract We have performed detailed investigations of the optical properties of strain-free In-rich InxGa1,xN (0.61 , x , 1.0) films that were grown directly on (0001) sapphire substrates by radio-frequency plasma-excited molecular beam epitaxy. In-composition dependence of photoluminescence peak energy for the InxGa1,xN films, measured at room temperature, exhibited a monotonic and smooth decrease with the increase in the In-composition, approaching to 0.66 eV of a strain-free InN film that was also grown directly on the sapphire substrate. The energy bowing parameter, b was determined to be 1.8 eV using these strain-free InxGa1,xN films. Structural properties of these films are also investigated in detail. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Preparation of ZnO thin films by MO-CVD method using bis(acetylacetonato) zinc(II) anhydrate fiberPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2010Shigeyuki Seki Abstract The MO-CVD method as a deposition process corresponding to the mass production of the high-quality ZnO film that can be used as an active layer in the thin film transistor is paid to attention. Bis(acetylacetonato) zinc(II) (Zn(acac)2) which has chemical stability and low toxicity is promising as the inexpensive raw material for CVD. The problem includes (1) pollution with water in process by character to easily take water of crystallization, and (2) the supply of the gas-phase raw material by sublimation should be not able to be controlled easily because it is a fine particle. In this study, Zn(acac)2 anhydrate fiber was prepared from Zn(acac)2 monohydrate powder by the sublimation process. Melting point of this fiber was almost same (,134 °C) as the monohydrate powder in N2 atmosphere. ZnO film was deposited on r-face sapphire substrate by MO-CVD process using Zn(acac)2 anhydrate fiber, successfully. RMS of the film flatness was 0.48 nm. This film had resistivity of 4.6 × 10,1 ,·cm, carrier electron density of 9.1 × 1017 cm,3 and Hall mobility of 15 cm2·V,1·s,1. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] GaN layer growth by HVPE on m-plane sapphire substratesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009Alexander Usikov Abstract Semipolar GaN layers were grown on m-plane sapphire substrates by HVPE. Insertion of AlxGa1,xN (x , 0.1-0.6) layer in-between m-plane sapphire substrate and GaN layer promoted to improve crystalline quality and to grow of semipolar (11-22) plane GaN layers. X-ray diffraction (11-22) ,-scan rocking curve FWHM of 298 arcsec was measured for a 30 ,m thick (11-22) GaN layer. Depending on growth conditions, m-plane GaN layer having micro-crystallites of other orientations (mainly of (11-24) plane GaN layer) was also grown. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Morphology control of GaN nanowires by vapor-liquid-solid growthPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2008Y. Inoue Abstract We synthesized GaN nanowires on sapphire substrate by metal organic chemical vapour deposition. The GaN nanowires were grown via vapor-liquid-solid (VLS) growth catalyzed with Ni thin film. Shape of nanowires depended on the substrate temperature and the growth pressure. The wire-like structure with high aspect ratio changed into the tapered structure with increasing substrate temperature, and with increasing the growth pressure. This dependency was attributed to the change of the surface diffusion length of source atoms. The VLS growth of GaN nanowire was revealed that the source species, absorbed at the eutectic droplet, came along the side wall of the nanowire as well as other semiconductor nanowires. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Formation of nitride laser cavities with cleaved facets on transferred laser diodes on GaAs substratesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008Wen-Chien Yu Abstract Smoothly cleaved facets with high reflectivities have been demonstrated on GaN laser diodes after the devices were transferred onto GaAs substrates. The GaN based laser diode structure was first fabricated by metal organic chemical vapor deposition (MOCVD) on c-plane sapphire substrates. The samples were then mounted onto thin GaAs substrates using wafer-bonding technology. Laser lift-off (LLO) technique was applied to remove the original sapphire substrate and transfer the GaN laser structure onto GaAs substrates. Since the cubic substrates have well-defined laser cavity cleavage facet, the GaN structures bonded onto the substrates also formed smooth facets after cleavage. The cleaved facets of GaN laser diodes have been characterized using atomic force microscopy (AFM) with less than 2 nm roughness. The present study demonstrated the feasibility of transferring GaN laser structures onto other more appealing substrates for formation of laser cavities. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optimization of underlying layer and the device structure for group-III-nitride-based UV emitters on sapphirePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008K. Iida Abstract Epitaxial lateral overgrowth (ELO) was applied for the growth of AlGaN on a sapphire substrate by metalorganic vapor phase epitaxy. Among several processes, the ELO of AlGaN on grooved AlGaN showed the best surface morphology and the lowest dark-spot density of 1×108 cm,2 as measured using cathodoluminescence. The light output power of a UV LED fabricated on ELO-Al0.25Ga0.75N on grooved Al0.25Ga0.75N was the strongest among several UV LEDs fabricated by different processes. The effect of the Al composition in the electron-blocking (EB) layer on the performance of UV LEDs was investigated. The UV LED with a low-Al-content EB layer showed high output power under a low-injection condition, while the output power of a UV LED with a high-Al-content EB layer did not saturate even under a high-injection condition. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optical properties of Na0.68CoO2 thin filmPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2007M. H. Hsu Abstract The optical reflectance of single-crystalline Na0.68CoO2 (thickness around 3000 Å) thin film has been measured over a wide frequency (40,55000 cm,1) and at temperatures between 20 and 300 K. The room-temperature optical conductivity spectrum displays a metallic character. In addition, one E1u phonon mode at about 518 cm -1 is identified, while the other four phonon peaks are due to the sapphire substrate. As the temperature is lowered, the Drude plasma frequency exhibits little temperature dependence, whereas the scattering rate monotonically decreases with decreasing temperature. Notably, the Drude scattering rate at 20 K is found to approach zero, consistent with the small residual resistivity, indicating high quality of Na0.68CoO2 thin film. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] In situ gravimetric monitoring of decomposition rate on the surface of (0001) c-plane sapphire for the high temperature growth of AlNPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007K. Akiyama Abstract The thermal stability of (0001) sapphire was investigated at atmospheric pressure using the in situ gravimetric monitoring (GM) method. The weight change of a sapphire substrate was monitored at various hydrogen partial pressures in carrier gas (P) at temperatures over 1200 °C. Although the sapphire substrate was stable up to 1450 °C in an inert carrier gas (P = 0.0 atm), sapphire decomposition started to occur at 1200 °C in H2 carrier gas (P = 1.0 atm). Moreover the activation energy and order of reaction for sapphire surface decomposition changed at approximately 1300 °C. These results indicate that the rate-limiting reaction for sapphire decomposition shifts near 1300 °C. (© 2006 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] Current spreading and thermal effects in blue LED dicePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2007K. A. Bulashevich Abstract We have applied simulations to study current the spreading and heat transfer in blue III-nitride light-emitting diodes (LEDs) with the focus on self-heating and its effect on the device characteristics. A conventional planar design of an LED die is considered for the heat sink through a sapphire substrate. The computations predict a great current crowding at the contact electrode edges, resulting in a non-uniform temperature distribution over the die. The thermal effect on the current-voltage characteristic, output optical power, and series resistance of the diode is analyzed and the theoretical predictions are compared with available observations. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Efficiency enhancement of 400 nm violet LEDs utilizing island-like GaN thick film by HVPE technologyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2007Jenq-Dar Tsay Abstract In this study, we develop a novel way to fabricate InGaN/GaN LED chips with special shape for improving the output power. Crack-free shaped GaN islands were first prepared on c-axis sapphire substrate by using HVPE selective area growth. By doing so, GaN islands with flat top surface and inclined side faces are obtained. Then, the InGaN/GaN LED structure was grown on the top surface of the GaN island subsequently. The output powers of the p-side up and the p-side down shaped LED chip are 1.4 and 2.2 times the output power of the cubic chip, respectively. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] AlGaN films grown on trenched sapphire substrates using a low-temperature GaNP buffer layer by MOCVDPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006K. Sumiyoshi Abstract A technique has been developed to grow low-dislocation-density AlGaN films in this paper. The AlGaN film is laterally overgrown on a trenched sapphire substrate with a low-temperature (LT) GaNP buffer layer by metalorganic chemical vapour deposition (MOCVD). The optical charactertics and microstructure of the AlGaN films have been invesigated by means of cathodoluminescence (CL), high-resolution X-ray diffraction (HRXRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. It is shown that the dislocation densities in the Al0.07Ga0.93N film are reduced to 8.7 x 108 cm,2 (by CL) and 2.7 x 109 cm,2 (by TEM) in the whole trenched sapphire, and 4.0 x 108 cm,2 (by CL) and 1.3 x 109 cm,2 (by TEM) in the trenched area. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Mechanisms of bending of threading dislocations in MOVPE-grown GaN on (0001) sapphirePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006R. Datta Abstract In this article, we describe possible mechanisms associated with the bending of threading dislocations (TDs) through 90° in GaN. In-situ ELOG using SiNx masking on a sapphire substrate and in-situ SiNx interlayer (IL) deposition on a GaN pseudo-substrate have been used to reduce the TD density in GaN. The bending of TDs through 90° is essential in order to reduce their numbers in the upper growing layer. The bending of TDs is facilitated by a change in growth mode, i.e. predominantly 2D to 3D and then 3D to 2D. A new mechanism is tentatively proposed which can explain the bending of all types of TDs (edge, screw, and mixed). This new mechanism is based on first, step formation at 3D island side facets when TDs terminate there, following which, depending on the subsequent change in growth mode (3D to 2D) and the direction of the atomic ledge movement, the TDs will bend over. (© 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] Comparison of ECR plasma pretreatment techniques for ZnO atomic layer epitaxy on the sapphire substratePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2004Kyoungchul Shin Abstract ZnO films were grown on sapphire substrates treated with ECR plasma by the atomic layer epitaxy (ALE) technique. ZnO nucleation enhancing effects of oxygen, hydrogen, and argon plasma treatments were compared. The incubation period for ZnO nucleation was measured by using scanning electron microscopy (SEM) and Auger electron emission spectrometric (AES) analysis. The incubation period for ZnO nucleation on the Al2O3 substrate not treated with plasma was more than 40 ALE cycles. The incubation period was shortened down to less than 35 cycles by argon or hydrogen ECR plasma pretreatment and to less than 30 cycles by oxygen ECR plasma pretreatment. It was found that a microwave power of 300W and a plasma exposure times of 10 min were appropriate for oxygen ECR plasma treatment of sapphire substrate surfaces to enhance ZnO nucleation. Higher power and longer exposure time would not be effective or would rather aggravate than enhance ZnO nucleation. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] GaN-free transparent structure for ultraviolet light emitting diodesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2004T. Nishida Abstract AlGaN-based light emitting diodes (LEDs) are expected to be the next generation of ultraviolet light (UV) sources. With the aim of achieving AlGaN-based UV-LEDs comparable to those of conventional blue and red LEDs, we have investigated the regular epitaxial growth, the fabrication of uniform and abrupt heterointerfaces, the optical characteristics of AlGaN-based nitride quantum structures, the validity of the band engineering, the p-n junction designs, radiative recombination and light extraction. Efficient and transparent UV-LEDs grown on a high-quality AlN-template layer on a sapphire substrate are free from binary GaN, and have great potential for lighting equipment and other applications. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Repeated Growing and Annealing Towards ZnO Film by Metal-Organic CVD,CHEMICAL VAPOR DEPOSITION, Issue 7-9 2009Chia-Cheng Wu Abstract ZnO deposited on sapphire substrate is investigated as a function of growth temperature in the range 350,650,°C. The surface morphology of ZnO structures changes significantly with increasing growth temperature. Though ZnO crystal quality and optical property can be improved under high growth temperature, ZnO is inclined to form nanostructures. Therefore, we propose the repeated growing and annealing (RGA) growth mode as a reliable and reproducible way for the growth of ZnO film. The RGA growth mode is performed at a growth temperature of 450,°C for 8,min, an anneal temperature of 650,°C for 20,min, and repeatedly switched between growing and annealing. Meanwhile, we compare the effects of annealing under Ar, N2, and O2, and found that a low resistivity of 3.4,×,10,3,, cm and a high mobility of 85.2,cm2 V,1 s,1 can be obtained annealing under N2. [source] Properties of InAs co-doped ZnO thin films prepared by pulsed laser depositionCRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2009J. Elanchezhiyan Abstract InAs co-doped ZnO films were grown on sapphire substrates by pulsed laser deposition. The grown films have been characterized using X-ray diffraction (XRD), Hall effect measurements, Atomic force microscope (AFM) and Field emission scanning electron microscope (FESEM) in order to investigate the structural, electrical, morphological and elemental properties of the films respectively. XRD analysis showed that all the films were highly orientated along the c-axis. It was observed from Hall effect measurements that InAs co-doped ZnO films were of n-type conductivity. In addition, the presence of In and As has been confirmed by Energy dispersive X-ray analysis. AFM images revealed that the surface roughness of the films was decreased upon the co-doping. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Development of 230,270 nm AlGaN-based deep-UV LEDsELECTRONICS & COMMUNICATIONS IN JAPAN, Issue 3 2010Hideki Hirayama Abstract We demonstrated AlGaN multi-quantum well (MQW) deep-ultraviolet (UV) light-emitting diodes (LEDs) with wavelengths in the range of 227.5 to 273 nm fabricated on high-quality AlN buffers on sapphire substrates grown by metal-organic chemical vapor deposition (MOCVD). We realized crack-free, thick AlN buffers on sapphire with a low threading dislocation density (TDD) and an atomically flat surface by using the ammonia (NH3) pulse-flow multilayer (ML) growth technique. We obtained single-peaked operation of an AlGaN-MQW LED with a wavelength of 227.5 nm, which is the shortest wavelength of AlGaN-based LED on sapphire. The maximum output power and the external quantum efficiency (EQE) of the 261- and 227.5-nm LEDs were 1.65 mW and 0.23% in room-temperature (RT) continuous-wave (CW) operation, and 0.15 mW and 0.2% in RT pulsed operation, respectively. © 2010 Wiley Periodicals, Inc. Electron Comm Jpn, 93(3): 24,33, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10197 [source] Fabrication of Vertically Well-Aligned (Zn,Mn)O Nanorods with Room Temperature Ferromagnetism,ADVANCED MATERIALS, Issue 22 2005M. Baik Vertically well-aligned (Zn,Mn)O nanorods (see Figure) that show ferromagnetic behavior at room temperature have been grown on sapphire substrates by chemical vapor deposition. The high optical quality of the nanorods has been demonstrated by photoluminescence spectroscopy. These nanowires may find use in future nanoscale magneto-optic and magneto-electronic applications. [source] High-temperature (1500,K) reciprocal space mapping on a laboratory X-ray diffractometerJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2007R. Guinebretière A laboratory X-ray diffractometer devoted to the in situ characterization of the microstructure of epitaxic thin films at temperatures up to 1500,K has been developed. The sample holder was built using refractory materials, and a high-accuracy translation stage allows correction of the dilatation of both the sample and the sample holder. The samples are oriented with respect to the primary beam with two orthogonal rotations allowing the registration of symmetric as well as asymmetric reciprocal space maps (RSMs). The association of a monochromatic primary beam and a position-sensitive detector allows the measurement of RSMs in a few minutes for single crystals and in a few hours for imperfect epitaxic thin films. A detailed description of the setup is given and its potential is illustrated by high-temperature RSM experiments performed on yttria-doped zirconia epitaxic thin films grown on sapphire substrates. [source] Microstructure of Nanocrystalline Yttria-Doped Zirconia Thin Films Obtained by Sol,Gel ProcessingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2008Benjamin Butz Nano- and microcrystalline yttria-stabilized zirconia (YSZ) thin films with a dopant concentration of 8.3±0.3 mol% Y2O3 were prepared with a variation in grain size by two orders of magnitude. A sol,gel-based method with consecutive rapid thermal annealing was applied to fabricate YSZ films, resulting in about 400 nm YSZ on sapphire substrates. The average grain sizes were varied between 5 nm and 0.5 ,m by heat treatment in the temperature range of 650°,1350°C for 24 h. High-resolution (HRTEM) and conventional transmission electron microscopy analyses confirmed specimens,irrespective of the thermal treatment,consisting of cubic (c -)ZrO2 grains with nanoscaled tetragonal precipitates coherently embedded in the cubic matrix. Energy-dispersive X-ray spectroscopy and HRTEM on a large number of specimens yielded a homogeneous yttria concentration within the grains and at the grain boundaries with the absence of impurities, i.e. silica at the grain boundaries. [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] | ||||||||||||||||||||||||||||