水熱法によるZnO単結晶の成長と特性評価(<小特集>バイオクリスタルにおける核形成・成長の制御機構)

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ZnO has been attracting much interest for the application of UV and blue light emitter. Growth of large high quality ZnO crystals is important not only for basic studies but also for application. On such a standpoint, we have grown bulk ZnO crystals by the hydrothermal method and studied their optical and electrical properties. Several seeds and sintered ZnO powder together with a mixture of KOH and LiOH aqueous solution were put into a Pt crucible. It was sealed and put in an autoclave to hold at 400℃ and 0,1 Gpa. Seed crystals were grown about 10 mm in dimension after 2 weeks. They were trans-parent and greenish yellow or pale yellow in color. The colors disappeared when the crystal was grown in an oxygen rich condition, suggesting that these colors were related to the deficiency in oxygen content in the crystal and that oxygen rich condition compensates the deficiency. The optical property of the crystal was studied by cathodoluminescence (CL) at room temperature. UV (band edge luminescence) and visible (related to deep levels) emissions were observed. In the +c growth sector (grown with Zn-surface), strong green emission (540 nm) was observed together with the UV emission. In the - c growth sector (grown with O-surface), weak orange emission (600 nm) and weak UV emission was observed. In the m growth sector, the UV emission was the strongest while the orange emission was weak. The green emission may be attributed to the impurities such as Cu, while the orange emission to the intrinsic defects such as O vacancies. The Zn surfaces tend to incorporate impurity atoms during growth. The O surfaces, on the other hand, tend to create some deep levels acting as nonradiative centers. In the m-growth sectors, where both Zn and O are facing to the surface, the density of the deep levels is the lowest among these three types. This result showed that it is preferable to use the m-region for the UV applications. Similar dependence of growth sectors were measured in the I-V characteristics.
日本結晶成長学会の論文
1999-09-30

水熱法によるZnO単結晶の成長と特性評価(<小特集>バイオクリスタルにおける核形成・成長の制御機構)

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