Evidence for relaxed and high-quality growth of GaN on SiC(0001) (original) (raw)
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physica status solidi (a), 1999
The band alignment at the SiC/GaN interface is of relevance for electronic devices such as the wide-gap emitter (GaN layer) SiC based heterostructure bipolar transistor. We extracted the valence band offset (VBO) at this heterojunction by depositing thin layers of GaN on 6H-SiC(0001) by means of plasma enhanced MBE and measuring in-situ X-ray photoemission spectra. Differently thick samples were considered, showing a trend in the shift of the Ga 3p core level position. This effect is connected to a band bending induced by internal polarization fields. EXAFS measurements on the same samples showed a relaxed growth already for the thinnest layer. We therefore infer that the field in the GaN originates from the spontaneous polarization, without piezoelectric contributions. The extracted value for the valence band discontinuity is 0X9 AE 0X1 eV, in good agreement with previous theoretical results. The fits of the EXAFS data do not exclude a possible C/N intermixing at the otherwise, when abrupt, unstable GaN/SiC interface.
Growth of GaN on SiC substrates by MBE
We report the growth of Al x Ga 1-x N alloys on (0001) sapphire by the method of Electron Cyclotron Resonance-assisted Molecular Beam Epitaxy (ECR-MBE). The films were doped n-type with silicon at carrier concentration levels from 10 16 to 10 19 cm -3 . SEM studies reveal smooth surface morphology consistent with the observed 3x4 surface reconstruction in the RHEED pattern. Independent determination of the Al-concentration and the lattice constant of the alloys shows that Vegard's rule is obeyed in the pseudo-binary GaN-AlN system. The bandgap of the alloys, determined by transmission and photoluminescence measurements, was found to depend linearly on Al-concentration.
Journal of Electron Spectroscopy and Related Phenomena, 2005
The valence band discontinuity and the interface formation of the n-type hexagonal GaN/SiC(0 0 0 1) heterointerface have been studied by means of angle-resolved photoelectron spectroscopy using synchrotron radiation. Gallium nitride thin films were grown on SiC(0 0 0 1) substrates by molecular beam epitaxy using either nitrogen plasma or ammonia gas as nitrogen source. The interface properties were investigated in situ by a combination of core level and valence band spectroscopy. The interface formation and the valence band offset of the epitaxial GaN films grown by the two methods have been compared. The GaN/SiC interface shows Si N bond formation and the measured valence band discontinuity is 1.02 ± 0.1 eV for the ammonia grown films and 1.10 ± 0.1 eV for the nitrogen plasma grown films. These values are in good agreement with the theoretical prediction and indicate that the band alignment of the GaN/SiC heterojunction is of the staggered type.
Atomistic investigation of various GaN (0001) phases on the 6H-SiC (0001) surface
Physical Review B, 1999
A number of superstructures of the GaN ͑0001͒ surface have been investigated systematically by reflection high-energy electron diffraction, scanning tunneling microscopy, and first-principles theoretical calculations. The GaN-thin films are grown on the Si-terminated 6H-SiC ͑0001͒ surface by an N plasma-assisted molecularbeam epitaxy under the Ga-rich condition. While the as-grown GaN surface is revealed to be a featureless 1ϫ1 structure, post-growth deposition of Ga at lower temperatures results in the formation of a series of ordered structures, such as 2ϫ2, 4ϫ4, 5ϫ5, 5ͱ3ϫ2ͱ13, ͱ7ϫͱ7, and 10ϫ10 in the order of the increasing Ga coverage. An 1ϫ1-Ga-fluid structure is obtained with the highest Ga coverage. Neither ordered structure nor smooth morphology has been observed under the N-rich regime. We conclude that the atomic structures of all these Ga-rich phases can be described best by a Ga-adatom scheme. We further show that the 5ϫ5 and 5ͱ3ϫ2ͱ13 phases are two configurations that exhibit a unique one-dimensional characteristic in the adatom arrangement. Their structures can be understood by Peierls distortion against Fermi-surface instability under the Ga-adatom scheme.
Cubic GaN epilayers grown by molecular beam epitaxy on thin β-SiC/Si (001) substrates
Applied Physics Letters, 2000
The molecular beam epitaxy of cubic GaN on Si͑001͒ substrates, which were covered by a 4 nm thick -SiC layer, is reported. The structural and optical properties of the cubic GaN epilayers were studied by transmission electron microscopy, high-resolution x-ray diffraction, and low-temperature photoluminescence measurements. We find clear evidence for the growth of cubic GaN layers almost free of hexagonal inclusions. The density of extended defects and the near band edge photoluminescence of the cubic GaN layers grown at substrate temperatures of 835°C is comparable to that of high quality cubic GaN epilayers grown by molecular beam epitaxy on GaAs ͑001͒ substrates.
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 &...
Growth of GaN on porous SiC and GaN substrates
Journal of Electronic Materials, 2003
We have studied the growth of GaN on porous SiC and GaN substrates, employing both plasma-assisted molecular beam epitaxy (PAMBE) and metalorganic chemical vapor deposition (MOCVD). For growth on porous SiC, transmission electron microscopy (TEM) observations indicate that the epitaxial GaN growth initiates primarily from surface areas between pores, and the exposed surface pores tend to extend into GaN as open tubes and trap Ga droplets. The dislocation density in the GaN layers is similar to, or slightly less than, that observed in layers grown on non-porous substrates. For the case of GaN growth on porous GaN the overgrown layer replicates the underlying dislocation structure (although considerable dislocation reduction can occur as this overgrowth proceeds, independent of the presence of the porous layer). The GaN layers grown on a porous SiC substrate were found to be mechanically more relaxed than those grown on non-porous substrates; electron diffraction patterns indicate that the former are free of misfit strain or are even in tension after cooling to room temperature. Significant changes in the stress of the overgrown layers on porous GaN were also found, as seen in line shifts of low-temperature photoluminescence spectra.