The phase behavior of evaporated copper and indium precursors for selenization

Abstract

In this paper we discuss the phase behavior and microstructure of sequentially evaporated indium-on-copper layer stacks deposited onto molybdenum-coated glass substrates. It was determined that both equilibrium and non-equilibrium phases can exist depending on processing. Indium evaporated onto copper, without intentional substrate heating and no subsequent annealing, resulted in the formation of the CuIn (JCPDS card 35-1100) alloy phase and an unreported f.c.c. phase of undetermined composition. Auger spectrometry and X-ray diffraction strongly suggested this to be a new CuIn alloy. Indium evaporated onto copper with substrate heating at 200 °C followed by uncontrolled cooling to room temperature strongly favored the formation of Cu₁₁In₉ in addition to the two phases previously mentioned. The lack of elemental indium in both cases, the presence of which is expected from phase diagram analysis, was attributed to kinetic limitations. Annealing of Cu/In layer stacks for 1 h at 200 °C immediately following indium deposition promoted the formation of elemental indium and Cu₁₁In₉ while simultaneously reducing the concentration of both CuIn and the new f.c.c. alloy phase. The implications of these observations are discussed with regard to future selenization experiments.