The effect of vacancy defects on the electronic properties of β-Ga2O3

Abstract

In this paper, the characteristics of oxygen vacancies (VO) and gallium vacancies (VGa) in β-Ga2O3 are studied using density functional theory. The performed relaxation analysis indicates that the relaxation of VGaⅡ increases its octahedral volume. Compared with the tetrahedron, the Ga atom of the octahedron surrounding VO is more stable. The formation energy results suggest also that VGa0 is expected to be most favorable in p-type β-Ga2O3, while VGa-3 is preferred in the n-type. The −3 charge state acts as a compensating acceptor, which reduces electron conductivity. VO+2, which acts as the compensation donor center, can easily form in p-type β-Ga2O3, while the VO0 forms readily in n-type β-Ga2O3. VGa at high density can exist in β-Ga2O3 in an oxygen-rich environment, while VO can exist under oxygen-poor conditions. The defect charge-state transition level reveals that VGa is a deep acceptor and VO is a deep donor. For VGa, the transition levels ε (0/-1), ε (-2/-1), and ε (-3/-2) can appear in the thermodynamic equilibrium system. However, for VOⅠ and VOIII, which are used as negative-U centers, only the transition level ε (2+/0) can appear in thermodynamic equilibrium. Furthermore, the calculated bandgap properties indicate that VGa is capable of introducing ferromagnetism in β-Ga2O3, while VO cannot. VGa introduces both acceptor levels and donor levels within the bandgap, which compensate each other, and they, thus, determine the acceptor characteristics of the system. The appearance of VO-introduced donor levels into the bandgap increases the overall electron concentration of the system. A Bader charge analysis shows that the vacancy defect can have a strong effect on the charge distribution of the crystal and alter the electronic characteristics of the crystal. The research results in this paper show that the electronic and magnetic properties of β-Ga2O3 can be changed significantly by introducing different types of vacancy defects with different charge states during the preparation process of the device. This can be done to meet specific performance requirements of a commercial electronic component.