Thin films of InP for photovoltaic energy conversion. Final report, July 5, 1979-July 4, 1980

Abstract

Research to develop a low-cost high-efficiency thin-film InP heterojunction solar cell, using the metalorganic chemical vapor deposition (MO-CVD) technique for InP film growth on suitable substrates is reported. Heterostructure devices of CdS/InP, using InP films prepared by CO-CVD, were prepared and characterized. The research effort involved three major technical tasks: (1) materials growth; (2) materials characterization; and (3) device fabrication and characterization. The principal results achieved in the investigations are as follows: (1) temperature-activated orientation-dependent background donor doping was observed in undoped epitaxial InP films; (2) p-type epitaxial InP films were prepared by Zn and by Cd doping during growth; (3) the efficacy of Cd doping was found to vary exponentially with the reciprocal of the deposition temperature in the range 650 to 730/sup 0/C; (4) Cd doping appeared to offer no clear advantages over Zn doping for preparation of p-type InP by the MO-CVD process; (5) GaP grown by MO-CVD was investigated as a possible intermediate-layer material for growth of InP films on low-cost substrates; (6) p/sup +/GaAs polycrystalline layers (p > /sup 19/ cm/sup -3/) were successfully prepared by Zn doping during MO-CVD growth on various low-cost substrates and used as surfaces for growth of p-type polycrystalline InP:Zn layers; (7) nCdS/pInP heterojunction solar cells were prepared by vacuum deposition of CdS onto p-type InP films grown by MO-CVD as well as on InP single-crystal wafers; (8) the best polycrystalline CdS/InP cells were obtained in structures on P/sup +/GaAs:Zn layers on both Mo sheet and Corning Code 0317 Glass; and (9) structure analyses of the Cds films used in the heterojunction cells indicated the presence of polycrystalline hexagonal CdS even in films grown on single-crystal InP films or bulk-wafer substrates. (WHK)