Disruption, atom distributions, and energy levels for Ge/GaAs(110), Ge/InP(110), and Ge/InSb(110) heterojunctions

We report a detailed room-temperature synchrotron-radiation photoemission study of Ge overlayer growth on n-type GaAs(110), InP(110), and InSb(110) in order to correlate changes in bonding configurations and atom distribution with the movement of the Fermi level in the substrate band gap and the evolution of the electronic properties of the Ge overlayer. For Ge/GaAs(110), the interface is abrupt, but substrate core-level line-shape analysis indicates changes in the boundary layer and unique interface bonding configurations. Ge adatoms induce substrate disruption for InP(110) and InSb(110), and there are coverage-dependent morphology changes as atoms dissociated from the substrate redistribute themselves in the thickening Ge overlayer. In atoms segregate to the Ge surface but exhibit no tendency to form clusters; P atoms remain near the buried Ge/InP interface; and Sb atoms are expelled to the overlayer surface. The deposition of Ge on GaAs and InP causes the Fermi level to move toward midgap at low coverage, but then move back toward the conduction band. The reversal in direction correlates well with changes in substrate core-level line shapes. Low-temperature studies of Ge/n-type GaAs did not show this reversal, but the final position of $E_F$ in the gap was the same. The fully developed valence-band discontinuities were 0.73, 1.03, and 0.12 eV for amorphous Ge/GaAs(110), Ge/InP(110), and Ge/InSb(110) heterojunctions, respectively.