Revealing the true bulk As-antisite defect in GaAs(110) using DFT calculations and STM/STS measurements

Understanding mid-gap states in bulk semiconductors has profound implications in electronic/optoelectronic device design. For instance, mid-gap state from As-antisite defect (As_Ga) is found to mediate below-band gap excitation at ~1560 nm (or 0.8 eV) [1,2]. Identifying and directly probing point defects in a semiconducting surface are thus important yet challenging. In this work, we were able to obtain the atomic and electronic characteristics of As_Ga in GaAs(110) akin to bulk-As_Ga using DFT calculations and STM/STS spectra. We found that the mid-gap state induced by As_Ga in bulk GaAs is well-reproduced by the As_Ga in the third layer of GaAs(110) [3]. We also found that the geometry and partial charge density of this defect mimics that of the bulk. Simulated and experimental STM images show an “asymmetric two-lobe” feature in the region around the defect. Using local density of states and STS spectra, we propose three peaks of characteristic energy levels corresponding to As_Ga. These results constitute the first report of surface electronic signatures of true bulk point defect close to the surface of GaAs(110).

[1] M. Tani et. al. Appl. Phys. Lett. 77 (2000) 1396.
[2] M.C. Escaño et. al. Mater. Res. Express 6 (2019) 055914.
[3] MC Escaño et. al. Appl. Surf. Sci. 511 (2020) 145590.