Heteroepitaxy of La2O3 and La2-xYxO3 on GaAs (111)A by Atomic Layer Deposition: Achieving Low Interface Trap Density

GaAs metal-oxide-semiconductor devices historically suffer from Fermi-level pinning, which is mainly due to the high trap density of states at the oxide/GaAs interface. In this work, we present a new way of passivating the interface trap states by growing an epitaxial layer of high-k dielectric oxide, La2-xYxO3, on GaAs(111)A. High-quality epitaxial La2-xYxO3 thin films are achieved by an ex situ atomic layer deposition (ALD) process, and GaAs MOS capacitors made from this epitaxial structure show very good interface quality with small frequency dispersion and low interface trap densities (D-it). In particular, the La2O3/GaAs interface, which has a lattice mismatch of only 0.04%, shows very low D-it in the GaAs bandgap, below 3 x 10(11) cm(-2) eV(-1) near the conduction band edge. The La2O3/GaAs capacitors also show the lowest frequency dispersion of any dielectric on GaAs. This is the first achievement of such low trap densities for oxides on GaAs.