【Member Papers】 Xidian University --- First-principles study of Mg-Ge co-doping to realize p-type β-Ga₂O₃ containing divacancy-interstitial complex defects

      Researchers from the Xidian University have published a dissertation titled "First-principles study of Mg-Ge co-doping to realize p-type β-Ga₂O₃ containing divacancy-interstitial complex defects" in Computational Materials Science.

Project Support

      This research received support from the National Natural Science Foundation of China (NSFC) through Grants No. U21A20503, No. 61974112, and No. 61974115. Additionally, funding was provided by the Science and Technology on Reliability Physics and Applications Technology of Electronic Component.

Background

      β-Ga₂O₃ is an ultra-wide bandgap (UWBG) semiconductor with a bandgap of 4.9 eV, a high breakdown field of 8 MV/cm, and a Baliga figure of merit of 3444, making it highly suitable for applications in high-power devices, deep ultraviolet (DUV) photodetectors, and transparent conductive films. However, one of the major challenges limiting its broader adoption is the difficulty in achieving p-type conductivity.

      While n-type β-Ga₂O₃ has been successfully achieved through doping with Si and Sn, enabling carrier concentrations between 10¹⁵-10²⁰ cm^-3, p-type doping remains elusive due to deep acceptor levels and high defect formation energies. Efforts to introduce p-type conductivity using elements like Zn, Mg, and N have faced high resistivity and deep acceptor levels, which hinder hole activation.

      One promising approach involves utilizing Ga vacancy (V_Ga) defects, which can act as acceptors. However, V_Ga typically has high formation energy, making it less effective for p-type conduction. Recent studies suggest that divacancy-interstitial complex defects (2V_Ga1-Ga_ic), where two Ga vacancies are coupled with an interstitial Ga atom, may act as a more stable acceptor complex.

      This study investigates the formation energy and electronic properties of these complex defects, exploring how Mg-Ge co-doping can enhance the p-type conductivity of β-Ga₂O₃ by reducing formation energy and shallowing acceptor levels.

Abstract

      This study focuses on the divacancy-interstitial complex defects in β-Ga₂O₃ (denoted as 2V_Ga1-Ga_ic) and enhancement of the p-type conductivity of β-Ga₂O₃ containing 2V_Ga1-Ga_ic by co-doping. The results indicate that single doping with Group IV elements (Si, Ge, and Sn) reduces the formation energy of 2V_Ga1-Ga_ic but increases the acceptor level. Ge doping has the most significant effect on the formation energy, decreasing the formation energy of 2V_Ga1-Ga_ic from 4.58 eV to 3.61 eV compared to the undoped case. In comparison, single doping with Mg and Zn atoms decreases the acceptor level of 2V_Ga1-Ga_ic but increases the formation energy. Mg doping has a better effect on the acceptor level, decreasing the acceptor level ε(0/−1) of 2V_Ga1-Ga_ic from 0.22 eV to 0.04 eV from the valence band top compared to the undoped case. The advantages of the two single doping can be combined by co-doping. Mg-Ge co-doping not only reduces the formation energy but also shallows the acceptor levels, thus improving the hole activation efficiency. Therefore, the p-type conductivity of β-Ga₂O₃ containing 2V_Ga1-Ga_ic can be improved by using Mg-Ge co-doping, and this new scheme provides a new perspective for the future realization of p-type β-Ga₂O₃.

Highlights

      The relative stability of five complex defects was investigated.

      Si, Ge, and Sn single doping can reduce the formation energy of the complex defect system.

      Mg and Zn single doping can reduce the acceptor level of the complex defect system.

      Mg-Ge co-doping can realize p-type doping of the complex defect system.

Conclusion

      In summary, we focused on divacancy-interstitial complex defects in β-Ga2O3 and the effect of doping on the properties of divacancy-interstitial complex defects. It is found that 2V_Ga1-Ga_ic is the most stable configuration among the five divacancy-interstitial complexes. Single doping with Si, Ge, and Sn atoms significantly reduces the formation energy of 2V_Ga1-Ga_ic. Among them, Ge doping proves to be the most favorable, especially under O-rich conditions, where the formation energy of Ge-doped 2V_Ga1-Ga_ic is reduced to 3.61 eV. Single doping with Mg and Zn atoms significantly reduces the acceptor level of 2V_Ga1-Ga_ic, with Mg doping having a better effect. Mg-Ge co-doping can combine the advantages of Ge doping and Mg doping. This co-doping not only reduces the formation energy of 2V_Ga1-Ga_ic but also shallows its receptor level, thus improving the p-type conductivity.