Vogt, S.; Petersen, C.; Kneiß, M.; Splith, D.; Schultz, T.; von Wenckstern, H.; Koch, N.; Grundmann, M.: Realization of conductive n-type doped α-Ga2O3 on m-plane sapphire grown by a two step pulsed laser deposition process. Physica Status Solidi A 220 (2023), p. 2200721/1-6
10.1002/pssa.202200721
Open Access Version
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 as well as a lower tin incorporation for higher substrate temperatures, indicating desorption or float-up processes that determine the incorporation of the dopants. Electron mobilities as high as 17 cm2V−1s−1 (at 1.4×1019 cm−3) and 37 cm2V−1s−1 (at 3.7×1018 cm−3) are achieved for tin and germanium doped α−Ga2O3 thin films, respectively. Further, a narrow window of suitable annealing temperature from 680 K to 700 K for obtaining ohmic Ti/Al/Au layer stacks was identified. For higher annealing temperatures a deterioration of the electrical properties of the thin films was observed suggesting the need for developing low temperature contacting procedures for α−Ga2O3 based devices.