Surface and interface properties of In0.8Ga0.2As metal–insulator–semiconductor structures

Abstract

More than two decades ago it was shown that the surface barrier of InxGa1−xAs alloys, positive, in depletion, and negative, in accumulation passes through zero at, or near, x=0.8. Consequently, the energy bands at the surfaces of In0.8Ga0.2As might be the same as in the bulk; i.e., at flatband. Electrical, galvanomagnetic, and surface photovoltage measurements made on transistor-like, gated, eight-arm, In0.8Ga0.2As metal–insulator–semiconductor structures confirm that the equilibrium surface Fermi level is, indeed, at flatband. Although the density of surface states is of the order 1012/cm2 applied gate voltages can displace, quasistatically, the Fermi level, from above the conduction band edge to the vicinity of the valence band edge. An interpretation of the data applied to this as well as to all of the other InxGa1−xAs alloys is based on Zunger’s “vacuum pining rule” and Walukiewicz’s Fermi level stabilization energy. The energies of the states which determine their surface barriers are not referred to their conduction and valence band edges. Instead, they are amphoteric charged defects located on a composition-independent reference level, located ∼4.95 eV below the vacuum level.