Atomic force microscopic study of surface morphology in Si-doped epi-GaAs on Ge substrates: effect of off-orientation

The Si-doped GaAs/Ge heterostructures have been grown under different growth conditions by low-pressure metal– organic vapor-phase epitaxial technique and investigated by atomic force microscopy (AFM). Our results indicate that the 6° offcut Ge substrate coupled with a growth temperature of ~675°C, growth rate of ~3 $\mu$ m/h and a V/III ratio of ~88 are optimum set of growth conditions for the buffer layer growth of GaAs/Ge heterostructure solar cell. The surface morphology was found to be very good on 6° off-oriented Ge substrate and the root mean square (rms) roughness was approximately 3.8 nm over $3\times3 \mu m^2$ area scan compared to 2° and 9° off-oriented Ge substrates.