Realization of Conductive n-Type Doped α-Ga2O3 on m-Plane Sapphire Grown by a Two-Step Pulsed Laser Deposition Process

Abstract

Structural and electrical properties of undoped and doped α-Ga2O3 thin films grown by pulsed laser deposition on m-plane sapphire in a two-step process are presented. A buffer layer of undoped α-Ga2O3 is introduced below the electrically active thin film to improve the crystal quality and enable the stabilization of the α-phase at lower substrate temperatures for sufficient dopant incorporation. Donor doping of the active layers with tin, germanium, and silicon, respectively, is realized below a critical substrate temperature of 600 °C. Depth-resolved X-ray photoelectron spectroscopy measurements on tin-doped samples reveal a lower amount of tin in the bulk thin film compared to the surface and a lower tin incorporation for higher substrate temperatures, indicating desorption or float-up processes that determine the dopant incorporation. Electron mobilities as high as 17 cm2 V−1 s−1 (at (Formula presented.)) and 37 cm2 V−1 s−1 (at (Formula presented.)) are achieved for tin- and germanium doping, respectively. Further, a narrow window of suitable annealing temperature from 680 to 700 K for obtaining ohmic Ti/Al/Au layer stacks is identified. For higher annealing temperatures, a deterioration of the electrical properties of the thin films is observed suggesting the need for developing low temperature contacting procedures for α-Ga2O3-based devices.