Exploring the feasibility and conduction mechanisms of P-type nitrogen-doped β-Ga2O3 with high hole mobility

Abstract

P-type doping of ultrawide-bandgap semiconductors, which are the key materials for fabrication of next-generation high-performance optoelectronic and electronic devices, is extremely difficult to achieve. The lack of p-type Ga₂O₃ has become a great obstacle to fabricate a full Ga₂O₃-based p–n homojunction for high-performance device applications. We demonstrate that N-doped β-Ga₂O₃ achieved by a phase transition from GaN to β-Ga₂O₃ possesses low formation energy and transition level ε(0/−), thereby with good N dopant solubility and low activation energy of N acceptors (0.355 eV). The delocalization effect, enhancement of valence band dispersion, and thus the decrease of the hole effective mass are predicted for N-doped β-Ga₂O₃ due to the hybridization of O 2p with N 2p and Ga 4s orbitals. Activated hole concentrations of 6.1 × 10¹⁵ and 2.1 × 10¹⁶ cm⁻³ at a valence band maximum are predicted for β-Ga₂O₃:N_O(III) obtained by the nonspin and spin-polarized calculations, respectively. The hole mobility is 1.3 cm² V⁻¹ s⁻¹ for undoped β-Ga₂O₃ and remarkably increases to 8.8 and 5.5 cm² V⁻¹ s⁻¹ for β-Ga₂O₃:N_O(III) obtained by the non-spin and spin-polarized calculations, respectively. The origins for the unusual increase of hole mobility are attributed to the decrease of the hole effective mass, and reduction in acoustic deformation potential scattering and optical phonon scattering due to the weakening of electron–phonon coupling by N-induced phonon stiffening for β-Ga₂O₃:N_O(III). The p-type conductivity of N-doped β-Ga₂O₃ is demonstrated theoretically and also experimentally with a Hall hole concentration of 3.19 × 10¹⁵ cm⁻³ and a Hall hole mobility of 23.1 cm² V⁻¹ s⁻¹ for N-doped β-Ga₂O₃ films, and the p-type conductivity mechanisms are clarified. These studies will open a new horizon for other p-type wide bandgap oxide semiconductors.