Growth kinetics and processings of copper indium diselenide-based thin films

CuInSe₂ (CIS)-based compound semiconductors are increasingly important absorber layer materials for thin film solar cells. A better understanding of the growth kinetics of CuInSe₂ thin films as a function of the process parameters would benefit the development of this technology.; The reaction kinetics for formation of CuInSe₂ from the bilayer structure InSe/CuSe was studied in-situ by high-temperature X-ray diffraction. The reaction pathway produces a diffusion barrier layer that can be schematically represented as InSe|CuSe → InSe|CuInSe ₂|CuSe. Two different analyses based on the Avrami and the parabolic rate laws suggest that the reaction is one-dimensional diffusion controlled. The estimated apparent activation energy from each model is 66.0 and 65.2 kJ/mol, respectively. The result demonstrates that the time-resolved high temperature X-ray diffraction provides a powerful method for studying the reaction kinetics of CuInSe₂ growth.; The thermodynamic driving force for formation of copper selenide phase and the grain size distribution in CuInSe₂ films was investigated. Large grains (∼a few μm) were observed in the CuInSe₂ films annealed with a CuSe layer while films annealed without this layer exhibited very small grain size (<0.2 μm). This result suggests a secondary grain growth mechanism driven by the surface-energy anisotropy is responsible for the increased grain size.; Epitaxial growth of CuInSe₂ and CuGaSe₂ on (001) GaAs substrates was attempted. The result shows that the crystalline structure and its quality strongly depends on the film stoichiometry, especially the [Cu]/[III] atomic ratio, with Cu-rich compositions showing higher crystalline quality.; A two-dimensional model of heat transfer in the growth reactor was developed for a rotating platen/substrate in the molecular beam epitaxial reactor that was used for film growth. Time-varying view factors were included in the model to solve the problem dynamically and to account for the fact that the platen rotating at a given angular speed. The modeling results predict the temperature uniformity on the substrate surface is good (≤±10 °C) at a set point temperature in the range 200 to 500°C and rotation rate of 20 rpm.