容量過渡分光法による半導体薄膜の評価

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Deep levels in semiconductors grown by MOCVD were investigated by DLTS and ICTS methods. The dependence of concentrations of levels on growth conditions was studied. Especially, the influence of interruption of growth that is often necessary for heteroepitaxial layers was investigated.For undoped GaAs, accumulation of carrier was induced by the interruption. The carrier is due to shallow level, the concentration being-1016cm-3. Furthermore, deep levels localized near the surface (within the thickness of 550nm) were observed. These consist of multiple or continuous levels. These were observed irrespectively of the growth condition.The interruption of growth at junction surfaces of pn-GaAs and Ga0.7 Al0.3 As caused pile of O that was not observed for undoped GaAs. This was confirmed by SIMS. The pile was entirely removed by thermal etching in the case of GaAs. However, this still remained for GaAlAs. Therefore, the status of O is different. New deep levels induced by thermal etching were observed for both cases. The condition for getting clean surface by thermal etching is now inquired.
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