Work

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

Year: 2025

Type: article

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 ∼21.8 Å 2 . In contrast, a second-layer V As exhibits an asymmetric two-lobe darker contrast, due to 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. • Subsurface vacancies represent defects that are intrinsic to GaAs • First direct probe of subsurface As vacancies (V As ) by STM • Symmetry of the STM images is affected by the defect’s depth from surface • STM contrasts explained by calculated partial charge density distribution • V As induces slightly dispersed gap states ∼1.24eV from valence band maximum

Source: Solid State Communications

DOI: 10.1016/j.ssc.2025.116172