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

Structural and electrical properties of undoped and doped α ‐Ga 2 O 3 thin films grown by pulsed laser deposition on m ‐plane sapphire in a two‐step process are presented. A buffer layer of undoped α ‐Ga 2 O 3 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 cm 2 V −1 s −1 (at ) and 37 cm 2 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 ‐Ga 2 O 3 ‐based devices.