Tuning the Electronic and Optical Properties of Pristine and p-Type Al _0.5 Ga _0.5 As Nanowire Photocathodes via Intrinsic Point Defects

In this work, the effects of intrinsic point defects on the electronic and optical properties of both pristine and p-type-doped Al_<i>x</i>Ga_1-<i>x</i>As nanowires are investigated through first-principles calculations. The formation energy, band structure, charge density difference, density of states, work function, and optical absorption coefficient are analyzed. Results indicate that defects are more prone to formation in the surface layer of nanowires, with a gradual increase in formation energy as defects migrate toward the core region. Band structure and charge density difference analysis reveal that defects such as Ga_in, Al_in, V_As, As_Ga, and As_Al introduce donor impurity within the bandgap. In contrast, defects such as As_in, V_Ga, V_Al, Ga_As, and Al_As exhibit acceptor impurity characteristics, leading to an elevated work function and hindered electron emission. The former effectively reduces the electron escape barrier, while the latter increases the work function and hinders electron emission. Moreover, p-type doping promotes the formation of antisite defects while suppressing the generation of interstitial defects and vacancy defects. Notably, as the As_Ga defect moves away from the p-type doping center, the local electron compensation efficiency diminishes, and the defect-induced donor energy level continuously shifts toward lower energy, resulting in a gradient reduction of bandgap. Furthermore, all defects can enhance the optical absorption capacity of Al_<i>x</i>Ga_1-<i>x</i>As nanowire photocathodes in the visible light range, especially for p-type doping nanowires.