Interface characterization of GaAs/Ge heterostructure grown by metalorganic vapor phase epitaxy

Abstract

GaAs/Ge heterostructures having abrupt interfaces were grown under different growth conditions and investigated by atomic force microscopy (AFM), cross sectional high resolution transmission electron microscopy (HRTEM), low temperature photoluminescence (LTPL) spectroscopy, electrochemical capacitance voltage (ECV) profiling and current/voltage (I/V) characteristics. Our results indicate that a 6° off cut Ge substrate coupled with a growth temperature of ~675° C, growth rate of ~3 μm/hr and a V/III ratio of ~88 is an optimum growth condition for the buffer layer growth of GaAs/Ge heterostructure solar cells. The surface morphology was found to be very good on 6° off oriented Ge substrate and rms roughness was ~30.8 nm over 10 × 10 μm2 area scan over 2° and 9° off oriented Ge substrates. The lattice indexing of HRTEM exhibited an excellent lattice line matching between GaAs and Ge substrates. The ECV profiler shows an excellent abruptness between the film/substrate interface of GaAs/Ge and also between various layers of the complete solar cell structures. Finally, the I/V characteristics of GaAs/Ge solar cells were analysed under AM0 conditio