Epitaxial growth of CuGaSe2 thin films by MBE Influence of the Cu Ga ratio

By molecular beam epitaxy MBE CuGaSe2 CGS thin films with varying Cu Ga ratios were grown epitaxial on GaAs 100 and stepped GaAs 111 A substrates. Cu Ga ratios from Cu poor to Cu rich were obtained. In this work the appearance of Cu crystallites on the surface of epitaxial CGS 001 layers are observed and strategies to avoid these precipitations are presented. High quality thin CGS films of around 100 nm thickness are obtained, enabling a detailed analysis of the electronic and chemical properties as well as of the crystal structure of the CGS surfaces. The electronic structure with respect to the Cu Ga ratio was characterized in situ by XPS and UPS. By LEED a 4x1 Cu poor and near stoichiometric and a 4x2 Cu rich reconstruction of a zinc blende structure were obtained. For CuGaSe2 112 the LEED pattern showed a 3x1 chalcopyrite reconstruction for Cu Ga ratios lt; 1. A 1x1 reconstruction of the chalcopyrite structure was observed for Cu rich 112 samples. The observed dependence of the surface reconstruction on the stoichiometry for CGS grown on GaAs has not been reported in literature so far. Additionally, for Cu rich stoichiometries a binary phase of Cu2 xSe appeared independently of orientation. The film morphology was investigated ex situ by SE