Growth of GaN on SiC(0001) by Molecular Beam Epitaxy (original) (raw)
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Properties of GaN epitaxial layers grown on 6H-SiC(0001) by plasma-assisted molecular beam epitaxy
Journal of Electronic Materials, 2001
The structural, electrical, and optical properties of GaN grown on 6H-SiC(0001) substrates by molecular beam epitaxy are studied. Suitable substrate preparation and growth conditions are found to greatly improve the structural quality of the films. Threading dislocation densities of about 1 × 10 9 cm-2 for edge dislocations and < 1 × 10 6 cm-2 for screw dislocations are achieved in GaN films of 0.8 µm thickness. Mechanisms of dislocation generation and annihilation are discussed. Increasing the Ga to N flux ratio used during growth is found to improve the surface morphology. An unintentional electron concentration in the films of about 5 × 10 17 cm-3 is observed, and is attributed to excess Si in the films due to a Si-cleaning step used in the substrate preparation. Results from optical characterization are correlated with the structural and electronic studies.
Role of Ga flux in dislocation reduction in GaN films grown on SiC(0001)
Applied Physics Letters, 2001
GaN films are grown by plasma-assisted molecular-beam epitaxy on SiC substrates. The width of the x-ray rocking curve for the (101̄2) reflection exhibits a distinct minimum for Ga/N flux ratios which are only slightly greater than unity. Correlated with this minimum, the surface morphology is somewhat rough, with a hill and valley topography. Based on transmission electron micrographs, the reduction in rocking curve width is attributed to enhanced annihilation of edge dislocations due to their tendency to cluster at topographic valleys.
Journal of Alloys and Compounds, 2017
The effects of growth temperatures and post-annealing treatment for GaN films by plasma-assisted molecular beam epitaxy are investigated. The heteroepitaxial GaN films were deposited on 4H-SiC substrates with 4 miscutting orientation at growth temperatures from 700 C to 800 C with a constant N/Ga flux ratio, while the post-annealing process was carried out at 800 C for 10 min. GaN films are characterized by reflective high-energy electron diffraction, field-emission scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, high-resolution X-ray diffraction and photoluminescence spectroscopy. For the growth at the temperature of 750 C, we can obtain a smooth surface, high percentages of GaeN bond and low R GaO/GaN revealing a more stable composition on the surface. The higher crystalline structure of GaN films can be also obtained with the minimum of threading dislocation density. The sharpest near band edge emission and lowest defect band emission can be observed for GaN films grown at temperature of 800 C. However, the surface roughness increases, and surface decomposition of GaN films occurs for the high-temperature growth. Moreover, post-annealing process can make the surface smoother, remove Ga droplets, and improve the stability of surface composition. After the post-annealing process, the increase of crystalline quality and optical property can be also demonstrated by the reduction of dislocation density and yellow band emission, respectively. In summary, the optimization of growth temperatures and post-annealing process can produce a high-quality GaN compound semiconductor for the applications in the future.
Lateral epitaxy and dislocation density reduction in selectively grown GaN structures
Journal of Crystal Growth, 2001
The results of a comparative study of the defect microstructures at different regions in epitaxial, monocrystalline GaN structures grown selectively within windows in and laterally over SiO 2 masks deposited on GaN/AlN/6H-SiC heterostructures are presented. The defects in the GaN grown within the SiO 2 windows were predominantly threading dislocations of mostly mixed character with Burgers vector b ¼ 1=3h1 1 " 2 3i and edge dislocations with b ¼ 1=3h1 1 " 2 0i with a density range of 10 9-10 10 cm À2 , as determined using transmission electron microscopy (TEM). The regions of lateral epitaxial overgrowth (LEO-GaN) contained short dislocation segments parallel to the interfacial planes, which were usually aligned parallel or nearly parallel to the h1 " 1 0 0i or h1 1 " 2 0i directions and with densities of 410 6 cm À2. Specific morphologies exhibited by the LEO-GaN were determined to be associated with the mechanism of stress relaxation. Finite element analysis of these complex heterostructures showed that the accommodation of the mismatches in the coefficients of thermal expansion among the different phases in the heterostructures was manifest in the formation of the curved surfaces observed in cross-sectional TEM.
MRS Internet Journal of Nitride Semiconductor Research
Discrete and coalesced monocrystalline GaN and AlxGa1−xN layers grown via pendeo-epitaxy (PE) originated from side walls of GaN seed stripes with and without SiNx top masks have been grown via organometallic vapor phase deposition on GaN/AlN/6H-SiC(0001) and GaN(0001)/AlN(0001)/3C-SiC(111)/Si(111) substrates. Scanning and transmission electron microscopies were used to evaluate the external microstructures and the distribution of dislocations, respectively. The dislocation density in the laterally grown sidewall regions and in the regions grown over the SiNx masks was reduced by at least five orders of magnitude relative to the initial GaN seed layers. Tilting of 0.2° in the coalesced GaN epilayers grown over the SiNx masks was determined via X-ray and selected area diffraction; however, tilting was not observed in the material suspended above the SiC substrate and that grown on unmasked stripes. A strong, low-temperature photoluminescence band-edge peak at ~3.45 eV with a FWHM of &...
Studies of Defect Structure in Epitaxial AlN/GaN Films Grown on (111) 3C-SiC
Nanomaterials
Several aspects such as the growth relation between the layers of the GaN/AlN/SiC heterostructure, the consistency of the interfaces, and elemental diffusion are achieved by High Resolution Transmission Electron Microscopy (HR-TEM). In addition, the dislocation densities together with the defect correlation lengths are investigated via High-Resolution X-ray Diffraction (HR-XRD) and the characteristic positron diffusion length is achieved by Doppler Broadening Spectroscopy (DBS). Moreover, a comparative analysis with our previous work (i.e., GaN/AlN/Si and GaN/AlN/Al2O3) has been carried out. Within the epitaxial GaN layer defined by the relationship F4¯3m (111) 3C-SiC || P63mc (0002) AlN || P63mc (0002) GaN, the total dislocation density has been assessed as being 1.47 × 1010 cm−2. Compared with previously investigated heterostructures (on Si and Al2O3 substrates), the obtained dislocation correlation lengths (Le = 171 nm and Ls =288 nm) and the mean distance between two dislocation...
Screw Dislocations in GaN Grown by Different Methods
Microscopy and Microanalysis, 2004
A study of screw dislocations in Hydride-Vapor-Phase-Epitaxy (HVPE) template and Molecular-Beam-Epitaxy (MBE) over-layers was performed using Transmission Electron Microscopy (TEM) in plan-view and in cross-section. It was observed that screw dislocations in the HVPE layers were decorated by small voids arranged along the screw axis. However, no voids were observed along screw dislocations in MBE overlayers. This was true both for MBE samples grown under Ga-lean and Ga-rich conditions. Dislocation core structures have been studied in these samples in the plan-view configuration. These experiments were supported by image simulation using the most recent models. A direct reconstruction of the phase and amplitude of the scattered electron wave from a focal series of high-resolution images was applied. It was shown that the core structures of screw dislocations in the studied materials were filled. The filed dislocation cores in an MBE samples were stoichiometric. However, in HVPE materials, single atomic columns show substantial differences in intensities and might indicate the possibility of higher Ga concentration in the core than in the matrix. A much lower intensity of the atomic column at the tip of the void was observed. This might suggest presence of lighter elements, such as oxygen, responsible for their formation.
The structure of GaN layers grown on SiC and sapphire by molecular beam epitaxy
Materials Science and Engineering: B, 1997
A comparative study of the defects at the interfaces and inside the layers was carried out in GaN/AlN epitaxial layers on SiC and sapphire. Whereas surface cleaning of the sapphire substrates is rather standardised now, the SiC substrates cleaning is still to optimise conditions, as the high densities of defects inside the epitaxial layers cannot be explained solely by the 3.54% lattice mismatch. The investigated specimens were grown by molecular beam epitaxy (MBE), either assisted by electron cyclotron resonance or an NH 3 gas source system to provide atomic nitrogen. Assuming that MBE is a growth technique more or less close to equilibrium, the observed defects are interpreted and a growth mechanism, for GaN layers on the stepped (0001) SiC and sapphire surfaces, is proposed. © 1997 Elsevier Science S.A.
Structural properties of GaN epilayers directly grown on on-axis 6H-SiC(0001) by plasma-assisted MBE
Journal of Crystal Growth, 1999
We report on the structural properties of a series of thin GaN epilayers directly grown on on-axis 6H-SiC(0 0 0 1) by plasma-assisted MBE. X-ray measurements show that the crystalline perfection of the layers steadily improves with "lm thickness. In fact, the density of threading defects detected by transmission electron microscopy is found to decrease drastically with the distance away from the GaN/SiC interface, "nally reaching a value of less than 5;10 cm\ at a layer thickness of 0.5 m. The formation mechanisms of the threading dislocations in the GaN "lms are discussed in consideration of the speci"c GaN/SiC interface structure.