Vapor Phase Epitaxy of Copper Chalcopyrites Having Wide Band Gaps

本课题组报道了以CuCl、GaCl_3和H_2S为原料，Ar为载气，在GaAs和ZnS/GaAs衬底上气相外延生长CuGaS_2的实验结果。在前人研究的基础上，本研究的目的是实现CuGaS_2的原子层外延生长（ALE），并探索控制CuGaS_2化学计量比的可能性，发现了在GaP衬底上交替供给金属氯化物和H_2S气体以提供一定量H_2S气体的成功ALE生长的证据。这种ALE生长是在同时加入CuCl和GaCl_3金属氯化物时发生的，表明黄铜矿结构是金属原子自排列的。发现了一种有趣的生长方向变化现象，这表明在生长过程中发生了金属原子的重排，从而提供了H_2S气体的周期变化。生长层上A_1模的拉曼散射强度基本恒定，低温下出现自由激子发射，这两种特性分别使生长层具有高的均匀性和高的质量，这一研究为ALE生长I-III-VI_2族化合物半导体提供了基本的认识，并有助于控制外延层的化学计量比等性能。

Successful vapor phase eptaxial growth of CuGaS_2 on GaAs and ZnS/GaAs substrates was reported by our group using CuCl, GaCl_3 and H_2S sources and Ar carrier gas. On the basis of the previous study, the purpose of this research is to attain atomic layer epitaxial growth (ALE) of CuGaS_2 and to search a possibility of controlling stoichiometry of this compound.Evidence of successful ALE growth on GaP substrates with alternate feeding of metal chrorides and H_2S gas was found for providing amount of H_2S gas. This ALE growth was found to occur under simultaneous feeding of metal chrorides of CuCl and GaCl_3, suggesting self arrangement of metal atoms for chalcopyrite structure. An intersting phenomenon of growth direction change which suggests an occurrence of rearrangement of metal atoms during growth was found for providing period change of H_2S gas. Essentially constant intensity of Raman scattering of A_1 mode over the grown layer and the appearance of free exciton emission at low temperatures incicate high uniformity and high quality of the layer, respectively.This study is considered to provide a basic understanding for ALE growth of I-III-VI_2 compound semiconductors and to lead to control of epitaxial layer properties including stoichiometry.