Microstructural revolution of CIGS thin film using CuInGa ternary target during sputtering process

Abstract

CuInGa (CIG) ternary targets were prepared by vacuum arc remelting and used to deposit CIG thin films through direct current (DC) sputtering. We adjusted the sputtering energy (1–2kWh) by tuning both the sputtering power and the accumulative sputtering time. The impact of the varying sputtering energy on the microstructure of CIG targets and thin films was subsequently investigated. The experimental results indicated that the compositional uniformity of CIG targets is strongly influenced by this parameter. CIG thin films with a flat topography, low porosity, and dense grain boundaries were obtained when targets were accumulatively sputtered at 1kWh. These films showed good compositional uniformity while the CIG targets were found to maintain their microstructural characteristics as compared to their as-melted counterparts. On the other hand, Cu(In,Ga)Se2 (CIGS) thin films, obtained by a selenization process, exhibited large faceted grains composed of a single chalcopyrite phase with a preferred orientation along the (112) plane. Accumulative sputtering of CIG targets at higher energies (e.g., 2kWh) resulted in phase transformation and loss of In material as a result of an excess of residual heat budget on the surface generated by Ar ions bombardment. The CIG thin films thus showed an In-rich composition ratio, thereby potentially leading to In-rich CIGS thin films containing traces of an InSe compound.