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 ) and 37 cm2 V−1 s−1 (at ) 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.