Preparation and Characterization of Crystalline Thin Films Belonging in the Cu-In-S System for High Conversion Efficiency Solar Cells

作为高转换效率太阳电池的基础研究，开展了CuIn-S系结晶薄膜的制备和表征工作。采用多源蒸发法在Si(001)衬底上外延生长CuInS_2、CuIn_5S_8及其混合物薄膜。X射线衍射和RHEED观察表明，CuInS_2薄膜不是在黄铜矿结构中结晶，而是在与衬底垂直的c轴与闪锌矿结构共存的Cu-Au结构中结晶。CuIn_5S_8薄膜为松弛尖晶石结构，具有较好的择优取向。在500℃下沉积的富铜CuInS_2薄膜为黄铜矿结构，并与铜-金结构和闪锌矿结构共存。首次测量了500℃下生长的含黄铜矿相的薄膜在近20K的光致发光光谱。除了施主-受主对发射外，还观察到了微弱而宽广的激子发射。光子能量和发射展宽被解释为不同晶体结构引起的不同发射的叠加。本研究的结果将有助于CuInS_2薄膜的生长，除了从未生长过的黄铜矿结构外，没有额外的相。

The preparation and characterization of crystalline thin films belonging in the Cu-In-S system were performed as the basic study for high conversion efficiency solar cells. The films were grown on Si (001) wafers using a multisource evaporation method.Thin films of CuInS_2, CuIn_5S_8 and mixture of these were epitaxially grown when the In source temperature was varied. XRD and RHEED observation showed that the CuInS_2 film did not crystallize in the chalcopyrite structure, but in the Cu-Au structure with the c-axis normal to the substrate coexisting with the sphalerite structure. The CuIn_5S_8 film crystallized in the relaxed spinel structure with fairly good orientation. No evidence of CuIn_3S_5 was found from the XRD patterns.The Cu rich CuInS_2 films deposited at 500℃ crystallized in the chalcopyrite structure coexisting with the Cu-Au structure and/or sphalerite structure. In films with the stoichiometric composition, however, the chalcopyrite phase was not found.The photoluminescence (PL) spectra of films grown at 500℃ including chalcopyrite phase were measured at near 20K for the first time. In addition to the donor-acceptor pair emission, the weak and broad exitonic emissions were also observed. The photon energy and broadening of the emission are explained as the superposition of different emissions caused by the different crystal structure.The results obtained in this study will be useful for the growth of CuInS_2 films without extra phases except for the chalcopyrite structure which have never been grown.