GaN Epilayers (gan + epilayer)

Distribution by Scientific Domains


Selected Abstracts


Metalorganic Chemical Vapor Deposition Growth of a GaN Epilayer on an Annealed GaN Buffer Layer

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2003
F. 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]


Structural and optical characterization of (11-22) semipolar GaN on m -plane sapphire without low temperature buffer layer

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010
Sung-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]


GaN/air gap based micro-opto-electro-mechanical (MOEM) Fabry-Prot filters

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007
E. Cho
Abstract Structural and optical properties of Fabry-Prot 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]


Epitaxial strain energy measurements of GaN on sapphire by Raman spectroscopy

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005
H. 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]


Improved crystallinity and polarity manipulation of MOVPE-grown GaN epilayers with deep sapphire-nitridation followed by Al-preflow at high temperatures

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003
B. 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 interlayer

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003
A. 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]


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 2007
Yoon 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]


Effect of growth temperature of AlN interlayers on the properties of GaN epilayers grown on c-plane sapphire by metal organic chemical vapor deposition

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2010
J. S. Xue
Abstract The effect of growth temperature of AlN interlayers on the properties of GaN epilayers grown on c-plane sapphire by metal organic chemical vapor deposition has been investigated by high resolution X-ray diffraction (HRXRD) and Raman spectroscopy. It is concluded that the crystalline quality of GaN epilayers is improved significantly by using the high temperature AlN (HT-AlN) interlayer in GaN buffers. The density of threading dislocation is reduced especially for edge type dislocations. Higher compressive stress exists in GaN epilayers with HT-AlN interlayer than with low temperature AlN (LT-AlN) interlayer, which is related to the reduction of strain relaxation caused by the formation of misfit dislocation. ( 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Morphological study of non-polar (11-20) GaN grown on r-plane (1-102) sapphire

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008
C. F. Johnston
Abstract In order to grow high quality non-polar GaN-based LED structures it is important to understand the mechanism of GaN growth by MOVPE on r-plane (1-102) sapphire. In this work, (11-20) GaN epilayers have been characterised at three stages of growth using high resolution X-ray diffraction (HRXRD), transmission electron microscopy (TEM) and atomic force microscopy (AFM). Following nucleation, 3D islands were grown, then the V/III ratio was lowered and the islands coalesced to form a smooth film. A series of symmetric XRD ,-scans obtained at different azimuthal angles revealed an anisotropy in the layers with respect to the [1-100] and [0001] axes. AFM scans show that the islands are elongated along the [0001] axis. TEM has been used to analyse the layers further. A high density of stacking faults (5x105 cm,1) and threading dislocations (4x1010 cm,2) was found in the film with 120 s high V/III growth followed by low V/III growth. Defects were found to run perpendicular and at ,60 degrees to the sapphire interface in uncoalesced "island" samples. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Raman scattering analysis of GaN with various dislocation densities

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008
T. Kitamura
Abstract We characterized GaN crystals with various dislocation densities by micro-Raman spectroscopy. Defects and Strain for the GaN layer were examined through measurements of the Raman shift and the width of the TO phonon bands. The broadening of Raman bands in GaN crystals occurred as the dislocation density increased. The up-shift of the peak frequencies corresponding to compressive strain was observed for the heteroepitaxial samples grown by MOCVD and MBE. The in-plane distribution of defects and strain in epilayers with various dislocation densities was also examined by Raman mapping. The Raman maps showed that the examined phonon frequency and band width in samples fluctuated spatially. The increase of dislocation density in GaN epilayers induced not only the broadening of Raman bands but also increase of fluctuation. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Spectrally-resolved nonlinear spectroscopy of in-plane anisotropy in uniaxially-strained GaN epilayers

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2005
Satoru Adachi
Abstract Spectrally-resolved four-wave mixing technique has revealed the internal structures of excitons in uniaxially strained gallium nitride films. Nonlinear response of four-wave mixing on the oscillator strength highlights the polarized excitons, and therefore allows us to map out the uniaxial strain field and the resultant anisotropic exchange splitting. Such a measurement gives a kind of crystalline analysis achieved in X-ray diffraction spectroscopy as well as information of the exciton fine structures including their temporal dynamics. ( 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Thermal activation of beryllium-related photoluminescence by annealing of GaN grown by molecular beam epitaxy

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005
Kyoungnae Lee
Abstract Surface polarity related differences in the optical activity of Be in GaN epilayers grown by rf-plasma molecular beam epitaxy are investigated. N-polar GaN doped with Be exhibits a significantly higher intensity of donor-acceptor pair (DAP) photoluminescence (PL) than similarly doped Ga-polar GaN, indicating the Be is incorporating at microscopically different sites, or possibly is forming different compensating complexes. Highly Be-doped Ga-polar GaN forms isolated polarity-inverted regions which then incorporate Be via the N-polar mechanism resulting in the DAP PL. High temperature annealing of the Ga-polar layers both under nitrogen/hydrogen mixtures and under pure nitrogen atmospheres activates the DAP PL. ( 2005 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 temperatures

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003
B. 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]


Improvement of the optical properties of GaN epilayers on Si(111): Impact of GaAs layer thickness on Si and pre-growth strategy

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003
Bablu K. Ghosh
Abstract This paper reports the effect of the GaN coating layer on the optical properties of GaN epilayers grown on GaAs/Si(111). Almost crack free GaN epilayers are found to be grown when a thin (,25 nm) GaN coating layer is inserted on 0.5 and 2 ,m GaAs layers at 550 C. Then nitridation of the GaAs layer is done through the coating layer by NH3 flow while the substrate temperature is ramped at 1000 C for epilayer growth. An attempt has also been made by implementing an additional GaN interlayer at 800 C while growth is continued for epilayer growth. For this growth strategy, cracks also happened without improvement of the epilayer quality. PL measurements show high excitonic peak energy and high excitonic to yellow band intensity ratio for GaN epilayers grown on the 0.5 ,m GaAs converted layer (CL) using a thin GaN coating layer. Those values are also found to be comparable/ better than for epilayers grown on 2 ,m CL. ( 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Reduction of Gallium Vacancy Concentration in Gallium Nitride Grown with Preheated Ammonia

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2003
S.-Y. Kwon
Abstract The use of ammonia preheater reduces the Ga vacancy (VGa) concentration in GaN. The epilayers grown with or without preheated ammonia had little differences in structural properties from X-ray diffraction and transmission electron microscopy. It was found, however, that the GaN epilayers grown with unheated ammonia had more charge compensation centers. The intensities of yellow luminescence (YL) in GaN epilayers grown with preheated ammonia decreased with Si doping, whereas those grown with unheated ammonia increased with Si doping. It is suggested that the use of preheated ammonia reduced the VGa concentration in GaN without altering structural properties. [source]