Impurity point defects in Mg doping Al0.5Ga0.5N: A first principles study

To gain a deeper understanding of doping in AlGaN, first-principles are employed to investigate various impurity point defects in Al_0.5Ga_0.5N. By comparing the formation energies of impurity point defects in Al_0.5Ga_0.5N under different charge states and growth conditions, the donor characteristics of the defects are revealed. The results show that Mg_N, O_N, Mg_Ga-O_N, H_i, and V_N-H_i exhibit donor characteristics under p-type conditions and may act as compensating centers in AlGaN. Meanwhile, the bonding states between impurity atoms and host atoms in Al_0.5Ga_0.5N are investigated. It is found that Mg, O, and H in impurity point defects all form chemical bonds with the atoms in AlGaN. Additionally, the thermodynamic transition levels of impurity point defects are also investigated with results indicating that V_N-H_i is most likely to undergo thermodynamic transitions in the p-type state. Moreover, the binding energies analysis reveals that Mg_Ga-O_N is the most stable impurity point defect in Al_0.5Ga_0.5N. Furthermore, the band structure studies indicate that Mg_N, V_Al-O_N, V_Ga-O_N, H_i, and V_N-H_i may introduce energy levels and undesired energy traps within the forbidden band. This study provides a detailed and quantitative analysis of Mg-doping impurity point defects in AlGaN, offering valuable insights into the doping behavior of Al_0.5Ga_0.5N.