Effects of growth temperature on atom distributions, Fermi-level positions, and valence-band offsets for Ge/n-type InP(110) heterojunctions.

Abstract

With synchrotron radiation photoemission, we have investigated Ge/InP(110) heterojunction formation at 300 and 60 K to correlate the movement of the surface Fermi level ${\mathit{E}}_{\mathit{F}}$ with the distributions of In and P in the growing Ge layer. Ge adatom deposition induces substrate disruption at both temperatures. For growth at 300 K, we observe In segregation to the surface. For growth at 60 K, In segregation is inhibited and the atoms remain at the interface, even when the system is warmed to 300 K. In contrast, P atoms, released by surface disruption, are retained at the buried interface at 60 and 300 K. The Fermi-level movement at 300 K as a function of coverage is unique in that it moves into the gap by \ensuremath{\sim}1-\AA{} deposition but then moves back toward the conduction-band minimum, demonstrating that the surface is not pinned. The surface photovoltage precludes measurement of the equilibrium ${\mathit{E}}_{\mathit{F}}$ position for formation at 60 K but annealing a 5-\AA{}-Ge/InP(110) interface to 300 K after formation at 60 K shows that the surface Fermi level was 440 meV from the conduction-band minimum. The fully developed valence-band discontinuity was 1.03\ifmmode\pm\else\textpm\fi{}0.08 eV, regardless of temperature.