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Microchannel epitaxy (MCE) of (001) GaAs with super-low supersaturation usually provides a very thin and wide lateral growth. However, it sometimes produces abnormal growth with a very low aspect ratio. In the abnormal growth, the layer grows very thick, and accordingly, the width becomes small. The aspect ratio is less than 1. The cause of the abnormal growth is studied and the edge effect is found to be responsible. The edge effect in liquid phase epitaxy (LPE) produces a high supersaturation near the periphery. Consequently, numerous steps are produced on the surface of the edge. This forms a step source in LPE and grows a thick layer with a very low aspect ratio. To suppress the abnormal growth, two types of mask patterns are proposed, which are designed to decrease supersaturation at the periphery. With the aid of the new masks, very wide and thin MCE layers are successfully obtained with high yields. For example, the width and thickness of an MCE layer are 210 and 6 µm, respectively, giving a high aspect ratio of 35.

Aluminum oxide was investigated as a mask material for the selective growth of GaN by liquid phase electroepitaxy in comparison with SiO 2 , SiN, and W. SiO 2 and W masks were dissolved in a solution and many polycrystals were generated on the SiN mask. Therefore, these masks are not suitable for selective growth. On the other hand, aluminum oxide was found durable in the solution, and growth selectivity was also achieved. Then, microchannel epitaxy was conducted using the aluminum mask by liquid phase electroepitaxy. Not only the selective growth but also the lateral growth of c-plane GaN with a width of about 8 µm was successfully achieved using the aluminum oxide mask.

High resolution transmission electron microscopy (HRTEM) is the effective technique for characterization of detailed structure of semiconductor materials. Oxygen is one of the important impurities in semiconductors. Detailed structure of highly oxygen doped silicon has not clearly investigated yet. This report describes detailed structure of highly oxygen doped silicon observed by HRTEM. Both samples prepared by Molecular beam epitaxy (MBE) and ion implantation were observed to investigate effects of oxygen concentration and doping methods to the crystal structure.The observed oxygen doped samples were prepared by MBE method in oxygen environment on (111) substrates. Oxygen concentration was about 1021 atoms/cm3. Another sample was silicon of (100) orientation implanted with oxygen ions at an energy of 180 keV. Oxygen concentration of this sample was about 1020 atoms/cm3 Cross-sectional specimens of (011) orientation were prepared by argon ion thinning and were observed by TEM at an accelerating voltage of 400 kV.

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