Research on electronic structure and optical properties of Ga0.75Al0.25N with vacancy defects

In order to investigate the influence of vacancy defects (Ga atom vacancy, Al atom vacancy and N atom vacancy) on the electronic structure and optical properties of Ga0.75Al0.25N, models of Ga0.75Al0.25N, Ga0.6875Al0.25N, Ga0.75Al0.1875N and Ga0.75Al0.25N0.9375 are built. Based on first-principles plane-wave ultrasoft pseudopotential method, we calculated the atomic structures, electronic structure and optical properties of vacancy models. The destruction of bonding structure caused by vacancy defects lead to the change of sp3 hybridized orbital, Which produces the result that the stability of Ga0.75Al0.25N decreases. Ga0.75Al0.25N tends to lose a Ga atom rather than an N atom. The vacancy defects can only change the bonding structure and E-Mulliken population near the vacancies. The Fermi levels of Ga0.6875Al0.25N and Ga0.75Al0.1875N enter into the valence bands and vacancy defect makes the crystals turn into p-type degeneracy semiconductors, while Ga0.75Al0.25N0.9375 turn into n-type. Moreover, electrical conductivity of Ga0.75Al0.1875N is the best, and that of Ga0.75Al0.25N0.9375 is the worst. The impact of vacancy defects on optical properties is mainly in the low energy region between 0 and 7 eV, and is negligible in the high energy region over 17.5 eV. The influence of Al vacancy on optical properties is the most obvious.