Atomically precise signatures of native subsurface As monovacancy defect in GaAs studied by STM imaging and DFT calculations

Abstract

We conducted scanning tunneling microscopy (STM) measurements and density functional theory (DFT) calculations to investigate surface arsenic vacancies (V-As) and intrinsic subsurface V-As in GaAs(110), revealing distinct STM features and symmetries depending on their depth from the surface. A surface V-As appears as a symmetric dark contrast at the missing As site with estimated size of similar to 21.8 A(2). In contrast, a second-layer V-As exhibits an asymmetric two-lobe darker contrast, due to relaxation and charge accumulation in the underlying Ga atoms. A third-layer V-As, however, shows a symmetric "butterfly-like" dark contrast, caused by charge accumulation in the lower layers along with charge depletion around the central surface As atom. DFT calculations using the modified Becke-Johnson local density approximation (mbJ-LDA) reveal that V-As in bulk GaAs introduce slightly dispersed, partially-filled gap states near the conduction band, confirming previous theoretical predictions. The above findings show key features to distinguish surface and native subsurface V-As relative to their location from the surface via STM. Moreover, our findings reveal details into the structural, energetic, and electronic properties of V-As in bulk GaAs, which can provide valuable insights into the desired V-As-induced below-band gap excitation in GaAs for terahertz and optoelectronic device applications.