DYNAMIC-COUPLING MODEL - INTERPRETATION OF TEMPERATURE-DEPENDENT, DOPANT-CONCENTRATION-DEPENDENT, AND COVERAGE-DEPENDENT SCHOTTKY-BARRIER FORMATION

Experimental results have shown that the position of the surface Fermi level EF for GaAs(110) depends critically on the bulk dopant concentration N and the temperature at which the measurements are made T, when adatoms of a wide variety of metals are deposited. For a specific N in the low dopant regime (1017 cm-3), coverage-dependent results show that EF remains close to the band extrema for both n- and p-type GaAs until the onset of metallicity. It then moves symmetrically into the gap, exhibiting a distinctive step in all cases. For higher dopant levels (2×1018 cm-3), EF movement is induced before the metallicity limit, and the step is reduced or lost altogether. Temperature-dependent studies for 20T300 K for a fixed number of adatoms demonstrate that EF can be moved reversibly into the gap, provided there are no morphological changes. These experimental results demonstrate that EF can be uniquely determined only when N, T, and are specified. Moreover, experimental results show that the net amount of charge transfer between the bulk and an adatom varies as a function of these three parameters. This paper presents a model, the dynamic-coupling model (DCM), that describes these N-, T-, and -dependent results. The model makes it possible to predict a maximum amount of band bending that will be observed for n- or p-type GaAs at any N, T, or. The DCM shows that the formation of a barrier after atom deposition is a self-regulated process that can limit further charge transfer and that wave-function coupling through the barrier contains the needed dependence on N and T.. AE © 1990 The American Physical Society.