Gate dielectrics on compound semiconductors

An oxide-based high-κ gate dielectric for GaAs has been developed using molecular beam epitaxy. A template layer of Ga2O3 is initially deposited on a GaAs(001) surface followed by the deposition of a bulk (GdxGa1−x)2O3 layer. The Ga2O3 layer serves to unpin the GaAs Fermi level while the GdGaO layer forms the high resistive layer to reduce leakage current through the dielectric stack. Deposition conditions during MBE were optimized for oxide surface morphology and interface quality. The use of molecular beam epitaxy also allowed for the control and uniformity of the ternary GdGaO layer along the growth direction. The midgap interface state density for the high-κ stack on GaAs of ≅ 2 × 1011 cm−2 eV−1, and a dielectric constant of k ≅ 20 were determined using electrical measurements. MOSFET devices were produced by replacing the GaAs cap layer in a PHEMT-type structure with a thick oxide layer. A contactless method was used to determine the mobilities from such devices which were comparable to those measured on a GaAs PHEMT using conventional Hall measurement.