Achieving n‐Type Conductivity in Epitaxial Ultrawide‐Bandgap β‐Ga2O3 Films via a Hf Doping Strategy

Abstract

Herein, the use of a Hf doping strategy in epitaxial β‐Ga2O3 thin films is demonstrated to substantially enhance the conductivity and simultaneously achieve an even wider bandgap. Epitaxial β‐Ga2O3 thin films with various Hf dopant ratios are fabricated by pulsed laser deposition. The doping impact on the structural, optical, and transport properties is systematically investigated. At an optimized doping regime of 1%–2% in molar ratio, the heteroepitaxial Hf‐doped β‐Ga2O3 (Hf‐Ga2O3) films grown on the MgO substrate achieve a high n‐type conductivity of 6.5 S cm−1, a carrier mobility of 1.8 cm2 V−1 s−1, a carrier concentration of 2.69 × 1019 cm−3, and an ultrawide bandgap of 4.9 eV. The electron transport is further enhanced for the homoepitaxial Hf‐Ga2O3 film that exhibits a conductivity of 1236 S cm−1 and an ultrahigh mobility of 113 cm2 V−1 s−1. Density functional theory calculations reveal the preferential atomic site of Hf dopants in the β‐Ga2O3 lattice and its impact on the optical bandgap. This study demonstrates an effective way to achieve degenerate n‐type doping in ultrawide‐bandgap semiconductors for developing optoelectronic and power electronic devices.