Eriko Takuma

Reduction of Planar Defect Density in Laterally Overgrown Cubic‐GaN on Patterned GaAs(001) Substrates by MOVPE

The metalorganic vapor phase epitaxy (MOVPE) growth of cubic-GaN (c-GaN) layers has been performed on the [110]-stripe patterned GaAs (001) substrates. The surface morphology of the laterally overgrown layer was much improved with the formation of the flat (311)A surfaces as the growth proceeded. It is shown that the c-GaN layer thicker than 20 μm was grown on GaAs(001) substrates with the stripe direction in [110] for 90 min. Microstructure and extended defect distribution in the laterally overgrown c-GaN films have been analysed by transmission electron microscopy (TEM). It is found that the planar defect (stacking faults and twins) density drastically decreases at the region away from the substrate toward the top of the c-GaN stripe. On the other hand, the dislocations become dominant. The density of the dislocations was found to be lower than 10 8 cm -2 . These results suggest that the lateral overgrowth on [110]-stripe-patterned GaAs (001) substrates via MOVPE is an efficient method for obtaining a low planar defect density c-GaN layer.

Laterally Overgrown GaN on Patterned GaAs (001) Substrates by MOVPE

The characteristics of single-crystal GaN regions obtained by selective-area and subsequent lateral overgrowth on stripe-patterned GaAs (001) substrates by MOVPE were studied. Under certain growth conditions, the surface kinetics of the MOVPE process result in lateral-growth of both hexagonal-GaN (h-GaN) and cubic-GaN (c-GaN) stripes with the appropriate mask stripe orientation, namely [110] and [110], respectively. The facet structure comprises the c-GaN stripes surrounded with (111) B facets and mixture facets of (311) A, (111) A, and an inversed (111) B for the stripe window opening along the [110] and [110] directions, respectively. The cross-sectional TEM micrographs showed that the h-GaN is laterally overgrown along the (111) B facets of the c-GaN stripes. For the [110]-stripes, the laterally overgrown h-GaN regions contained a very low density of dislocations (< 10 8 cm -2 ). On the other hand, for the [110]-stripes, a large reduction of stacking fault density was found in the overgrown c-GaN regions. We demonstrated that both high quality h-GaN and c-GaN films were successfully grown on the stripe-patterned GaAs (001) substrates by MOVPE.

Chemical Structure Analysis of a Σ 9 Grain Boundary in α-SiC by Arhvtem

Grain boundary chemical structure of high purity α silicon carbide was investigated by an atomic resolution high voltage transmission electron microscope (ARHVTEM). Each of a ‘darker’ spots and each of the ‘brighter’ spots in the image have been identified to be silicon (Si) and carbon (C). Two (0001)/(1 1 07) Σ 9 CSL grain boundaries were observed. One boundary showed a rigid body translation of 1/3 1 00> to the component crystals and the other did not. The unit period of the boundary was determined to 2.26 nm along >11 2 0

Atomic and Electronic Structure of Interfaces at Sic Studied by Indirect Super Hrtem and Electron Spectroscopyn Imaging

Obtaining electronic and atomic structure of material simultaneously is very important for developing the nano-technology. In this paper, we demonstrate that atomic and electronic structure of an interface can be extracted with combination of Gerchberg-Saxton indirect microscopy and electron spectroscopy imaging (ESI) technique. Basically, Gerchberg-Saxton algorithm includes two projections. Projection in the real space is a maximum entropy (ME) de-convolution process and in reciprocal space is an amplitude substitution process. It has been shown that Gerchberg-Saxton algorithm can extend the structural resolution to near 0.1nm. An application case of Gerchberg-Saxton algorithm to solve the atomic structure for 3C-polytypic SiC boundary is shown. ESI spectrum processed by FFT interpolation, maximum entropy de-convolution and wavelet transformation allow us to extract 2-dimensional map of the sp 2 /sp 3 with a sub-nanometer resolution. Grain boundary and interface at SiC are good candidates for this study, since the bond distance of Si-C is slightly less than 0.1nm which is not routinely resolvable using a FEG TEM and Si-L (99eV) and C-K-edges (283 eV) locate in a reasonable energy range. The resultant electronic structure can be compared with that calculated using WIEN97. An example of quantitative analysis on 2-dimensional sp 3 /sp 2 map deduced from the C K-edge of ESI spectra acquired from 6H-SiC is given.