Initial growth of Al on GaAs(001) and electrical characterization of the interface

Abstract

The formation of the interface between GaAs(001) and Al was studied by reflection high-energy electron diffraction (RHEED) and Auger electron spectroscopy (AES). All growth was performed by molecular beam epitaxy. Two surface reconstructions defined the native surface: c(2×8) and (4×6). In the studied temperature interval, 268 to 673 K, two temperature ranges were found. Above 550 K no nucleation was observed. At lower temperatures the growth of the first monolayer (ML) was detected as a linear (temperature independent) increase of the Auger signal with coverage. In the coverage range between 1 ML and the point of nucleation the Auger signal became more nonlinear. Both the Al and Ga Auger energies shifted toward metallic states. This shift, however, decreased with substrate temperature. The event of nucleation as observed by RHEED had a clear temperature dependence only when starting the growth from the c(2×8) surface. Evidence was found by both AES and electrical characterization that increasing temperature caused an intermixing at the interface. Electrical characterization of the interface was made by capacitance-voltage (C-V) and current-voltage (I-V) techniques. Averaging over a large number of diodes gave the Schottky-barrier height φb ≊0.75 eV for both techniques. No dependence on the initial surface reconstruction was found but excess Ga gave a larger barrier while excess As typically gave a lower barrier. Annealing the interface usually increased the Schottky barrier and increased the ideality factor above ∼1.05.