Achieving p-type conductivity in wide-bandgap SnO2 by a two-step process

Wide bandgap SnO2 usually shows n-type conductivity due to intrinsic defects. Herein, we demonstrate the achievement of p-type conduction in SnO2 with a two-step process, in which 3.3 at. % Mg-doped SnO2 epitaxial films were first grown on c-Al2O3 by pulsed laser deposition and then annealed in an oxygen atmosphere at proper temperature and time. An activation energy of around 85 meV revealed by temperature-dependent resistance measurements verifies Mg as a shallow acceptor in the p-type doping of SnO2. The post-annealing treatment at suitable temperature and time was found to be crucial to greatly enhance the p-type conductivity of Mg-SnO2 by removing the interstitial Mg while maintaining the substitutional Mg in the SnO2 lattice. A hole concentration of 1.43 × 1017 cm−3 and a hole mobility of 4 cm2 V−1 s−1 as determined by Hall-effect measurements were achieved for a sample annealed at optimized conditions of 600 °C and 0.5 h. The achievement of high-quality p-type Mg-SnO2 epitaxial films demonstrates high potential in developing advanced optoelectronic devices based on p-n junctions of SnO2.