A compound semiconductor structure is provided, which includes a GaAs-based supporting
semiconductor structure having a surface on which a dielectric material is to be
formed. A first layer of gallium oxide is located on the surface of the supporting
semiconductor structure to form an interface therewith. A second layer of a Ga-Gd
oxide is disposed on the first layer. The GaAs-based supporting semiconductor structure
may be a GaAs-based heterostructure such as an at least partially completed semiconductor
device (e.g., a metal-oxide field effect transistor, a heterojunction bipolar transistor,
or a semiconductor laser). In this manner a dielectric layer structure is provided
which has both a low defect density at the oxide-GaAs interface and a low oxide
leakage current density because the dielectric structure is formed from a layer
of Ga2O3 followed by a layer of Ga-Gd-oxide. The Ga2O3
layer is used to form a high quality interface with the GaAs-based supporting
semiconductor structure while the Ga-Gd-oxide provides a low oxide leakage current density.
