Magnetic Behavior of As-antisite Defect in Low-temperature GaAs from First-principles Bandstructure with Spin Orbit Interaction

Study of defect’s nature in wide-gap semiconductor can give light into its use as THz detector/emitter. In low-temperature GaAs (LT-GaAs), a two-step photon absorption via mid-gap states is proposed to explain the LT-GaAs-based PC’s detection of THz radiation when probed with 1.55μm probe laser. So far, within first-principles, the defect’s magnetic properties using realistic defect concentration (1.0-1.3%) and within the broken inversion symmetry of GaAs is still lacking. Here, DFT calculations on a 216-atom GaAs bulk using hybrid exchange correlation functionals are conducted. The symmetry is accounted for by including spin-orbit (SO) interaction via projector augmented wave method. We found that at the level of DFT+SO, a 1.46eV band-gap and 0.337eV split-off band at Γ are obtained in agreement with experiments (1.43eV, 0.341eV). Among the defects tested: As-antisite, Ga-antisite and Ga-vacancy, the As_Ga leads to a mid-gap state. Spin-resolved bandstructure of the GaAs with As_Ga, reveals a paramagnetic nature of the defect, in agreement with ESR. The non-split behavior of the mid-gap state is due to induced tetrahedral symmetry when a Ga atom is replaced by As. The state arises from charge density within the tetrahedra and not solely on As_Ga.