Popp, A.; Pettenkofer, C.: Epitaxial Thin Films of CuGaSe2 Prepared on GaAs (001) Electronic Structure and Morphology. In: 2016 IEEE 43rd Photovoltaic Specialists Conference (PVSC)Piscataway, NJ: IEEE, 2016. - ISBN 978-1-5090-2724-8, p. 480-484
10.1109/PVSC.2016.7749640
Abstract:
Abstract — CuGaSe2 with varying Cu/Ga ratios were grown epitaxial on GaAs (100) and stepped GaAs (111)A substrates by molecular beam epitaxy (MBE). A Cu/Ga stoichiometry range from Cu-poor to Cu-rich (0.51-1.65) was prepared. Depending on the stoichiometry for the (001) orientation a single domain (4x1) reconstruction of the zinc blende surface periodicity was determined by low energy electron diffraction (LEED) for Cu-poor and near stoichiometric samples. For Cu-rich samples instead, a (4x2) reconstruction was found. For CuGaSe2 (112) the LEED pattern showed a (3x1) reconstruction for Cu/Ga ratios < 1. A (1x1) reconstruction of the chalcopyrite structure was observed for Cu-rich (112) samples. In addition, for Cu-rich stoichiometries a secondary phase of Cu2-xSe appeared for both orientations. The electronic structure with respect to the Cu/Ga ratio was investigated by XPS and UPS. Supplementary an investigation of the film morphology was done ex-situ by SEM. In addition to conventional MBE, high quality films could be prepared by using the GaAs (100) substrate at elevated temperature as gallium source instead of an external gallium source.