Growth of p-type ZnO single crystal films by photo-assisted metal-organic chemical vapor deposition

II-VI化合物半导体中，ZnO有望成为高效紫外半导体激光器的材料。然而，高质量p型薄膜的生长是困难的。在本研究中，我们通过MOCVD对ZnO薄膜的低温生长进行了如下表征：1。采用紫外原位吸收法研究了源物质的分解温度、Zn金属有机物与氧源在气相中的过早反应以及载气（H_2, N_2）的差异。根据以上结果选择了分解温度低、早反应性低的原料。结果表明，生长温度在400℃左右时，t-丁胺适合作为氮掺杂的源材料。ZnO薄膜的生长采用MOCVD法，在低于400℃的生长温度下，以二甲基锌或二异丙基锌和异丙醇或正丁醇为原料，生长出具有镜面的ZnO薄膜。以自由激子发射为主的光致发光光谱表明制备了高纯度的ZnO薄膜。然而，改变源材料中n型杂质的掺入成为了一个问题。通过这个问题，薄膜的电子浓度为10^<18> ~ 10^<19>cm^<-3>，这个值并没有提高。这些实验没有显示光照射对底物的影响。氮掺杂在低II/VI条件下进行氮掺杂。低温光致发光光谱、拉曼光谱和霍尔效应表征表明，得到了10^<18> ~ 10^<19>cm^<-3>的氮掺杂。但由于未掺杂薄膜的电子浓度较高，最佳空穴浓度仅为10^<18>cm^<-3>数量级。提高原料纯度和光照射对MOCVD的影响有待进一步研究。

II-VI compound semiconductor, ZnO is expected as a material for high efficiency uv semiconductor lasers. However, the growth of high quality p-type thin films is difficult. In this study, we have performed the characterization for the low temperature growth of ZnO films by MOCVD as shown below.1. The decomposition of source materialsThe decomposition temperature, premature reaction between Zn metal organics and oxygen sources in vapor phase and the difference of carrier gas (H_2, N_2) are investigated by in situ uv absorption measurements. The source materials with low decomposition temperature and low premature reactivity were selected using above results. It was found that t-butylamin is suitable for the source materials for nitrogen doping at the growth temperature around 400℃.2. The growth of ZnO thin filmsThe growth of ZnO thin films with specula surface were grown by MOCVD at the growth temperature below 400℃ using dimethylzinc or di-isopropropylzinc and isopropylarchol or t-butylarchol. The photoluminescence spectra dominated by free exciton emission indicate that the high purity ZnO films were obtained. However, incorporation of n-type impurities of source materials became a problem by changing the source rot. By this problem, the electron concentration of the films were 10^<18>〜10^<19>cm^<-3>, and this value have not been improved. The effects of photo-irradiation to the substrate were not shown in these experiments.3. Nitrogen dopingNitrogen doping was carried out at low II/VI conditions. The characterizations by low temperature photoluminescence spectra, Raman spectra and Hall effect show that nitrogen incorporation of 10^<18>〜10^<19>cm^<-3> was obtained. However the best hole concentration was only the order of 10^<18>cm^<-3> because of high electron concentration of undoped films.The improvement of purity of source materials and the effect of photo-irradiation for MOCVD should be investigated.