P-type Inversion at the Surface of β-Ga₂O₃ Epitaxial Layer Modified with Au Nanoparticles

The electric properties and chemical and thermal stability of gallium oxide β-Ga₂O₃ make it a promising material for a wide variety of electronic devices, including chemiresistive gas sensors. However, p-type doping of β-Ga₂O₃ still remains a challenge. A β-Ga₂O₃ epitaxial layer with a highly developed surface was synthesized on gold electrodes on a Al₂O₃ substrate via a Halide Vapor Phase Epitaxy (HVPE) method. The epitaxial layer was impregnated with an aqueous colloidal solution of gold nanoparticles with an average diameter of Au nanoparticle less than 5 nm. Electrical impedance of the layer was measured before and after modification with the Au nanoparticles in an ambient atmosphere, in dry nitrogen, and in air containing dimethyl sulfide C₂H₆S (DMS). After the impregnation of the β-Ga₂O₃ epitaxial layer with Au nanoparticles, its conductance increased, and its electric response to air containing DMS had been inversed. The introduction of Au nanoparticles at the surface of the metal oxide was responsible for the formation of an internal depleted region and p-type conductivity at the surface.