Properties of polycrystalline GaAs films grown on CMG coverglass for space solar cell application

Polycrystalline GaAs films have been grown on Pilkington CMG cover-glass as a substrate at relatively low temperature by MOCVD. The substrate temperature (T_s) was varied from 450°C to 550°C, while other conditions were kept constant. Preferential orientation and grain size of the films grown at ≥500°C are proved to be [111] and 0.5-1.0μm by XRD and AFM, respectively. Both of the absorption coefficient and the optical bandgap are found to be equivalent to those of single crystal GaAs. Photoluminescence is confirmed from doped GaAs films at RT and from undoped films at 77K, both of which have not been observed in the case of using a quartz substrate. The films are considered to be applicable for space solar cells.