In SituInvestigation of Band Bending during Formation of GaAs-Ge Heterostructures

Symmetry-forbidden phonon Raman scattering is used to investigate in situ the formation of GaAs-Ge heterojunctions. Under epitaxial growth conditions the band bending in GaAs induced by the first monolayers of Ge decreases strongly for thicker overlayers. For amorphous overlayers the Fermi level remains pinned around midgap. A simple model is presented which explains the observed behavior. The development of the Ge phonons demonstrates crystalline growth for substrate temperatures Tg>~300 K and amorphous growth for Tg=100 K.