A first-principles study of structural and electronic properties of Ga1−xAlxAs alloys

A first principles full potential self-consistent linear muffin tin orbital (FPLMTO) method alongwith density functional theory in the local approximation has been employed to investigate the structural and electronic properties of seven Ga1−xAlxAs alloys in their ordered and random configurations. A linear (non-linear) variation of the lattice constant with the concentrations of the constituent atoms is seen for the ordered (random) structures. A direct to indirect band gap crossover takes place for x=0.375. Also, a band gap bowing below and above the crossover for both the direct and indirect band gaps is seen. The direct and indirect band gaps obtained for the ordered structures are in very good agreement with the photoluminescence and absorption data available. Our results support the occurrence of the well ordered structures in the alloys.