Study of pit formation in MBE grown GaP on misoriented Si

GaP-based alloys can be grown lattice-matched to Si, making them an attractive choice for use in Si-based multijunction solar cells. This work focuses on the growth of GaP on Si with the aim to improve the surface quality of GaP. The Si wafers used in this study were of precise (001), (001) 4 degrees offcut toward [110], and (001) 6 degrees offcut toward [110] orientations. GaP of high crystalline quality was grown, and high-resolution x-ray diffraction and atomic force microscopy (AFM) measurements revealed the presence of pits on the surface of GaP. Similar pits were also observed on surface of Si post growth when AFM imaging was done after chemically etching the GaP layers. The use of offcut wafers demonstrated a reduction in the pit density from over 100 mu m(-2) to values less than 1 mu m(-2) in both GaP and Si.