Thermodynamic prediction and experimental verification of optimal conditions for the growth of CuGa0,3In0,7Se2 thin films using close spaced vapor transport technique

Abstract

The aim of this work is to predict optimal conditions for growing good quality crystalline thin films using close spaced vapor transport (CSVT) technique. A thermodynamic model was developed and tested for the Cu–Ga–In–Se–I system to describe the deposition of CuGa0,3In0,7Se2 (CIGS). We considered a multiphase mixture containing 48 chemical compounds derived from the combination of the simple elements Cu, Ga, In, Se and I. The minimization of the Gibbs energy of the system was performed to calculate the composition of the mixture at the equilibrium state. In this way, the solid phase composition with possible impurities was predicted for various source temperature (TS) and iodine pressure (PI2). The conditions of stoichiometric and quasi-stoichiometric deposition are from 400 to 600°C for TS and from 30Pa to 14kPa for PI2. These optimal conditions were tested experimentally at 475°C, 500°C, 525°C and 550°C. The elaborated CIGS thin films were of good quality as revealed by X-ray diffraction and scanning electron microscopy. The experimental results proved that the thermodynamic model is a helpful tool for the prediction of the optimal conditions in the CSVT process.