First-principle study of the native defects in GaAs saturable absorbers

Abstract

The change of atom configuration in GaAs, caused by intrinsic point defects (Ga and As vacancies, Ga and As antisites, Ga and As interstitials), is first calculated by a plane wave pseudo-potential method with the generalised gradient approximation in the frame of density functional theory, and the most stable structure is obtained. Then, the formation energy of each kind of the native defect is calculated, by which the possibilities of the six kinds of point defects to be formed during crystal growth are analysed. The defect energy levels corresponding to each kind of the native point defect and their electron occupancy are analysed from the aspect of density of states. Finally, the elastic constants of GaAs saturable absorbers with native point defects are calculated, and the impacts on the elastic properties brought by native point defects are studied. The values of defect energy levels obtained will be helpful in ascertaining the mechanism of the EL2 deep level in the GaAs saturable absorber, and the analysis of the elastic properties of a GaAs crystal with native point defects will be helpful in guiding the application of the GaAs crystal as a saturable absorber in passively Q-switched lasers.