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 degrees offcut Ge substrate coupled with a growth temperature of similar to 675 degrees C, growth rate of similar to 3 mu m/h and a V/III ratio of similar to 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 degrees off-oriented Ge substrate and the root mean square (rms) roughness was approximately 3.8 nm over 3 x 3 mu m(2) area scan compared to 2 degrees and 9 degrees off-oriented Ge substrates.