特集「革新的材料-デバイスの創出を見据えた分野横断的表面科学研究」
高効率テラヘルツデバイス開発のための第一原理計算に基づくSTMシミュレーションによる低温成長GaAsのバルク点欠陥の直接同定
2023 年 66 巻 1 号 p. 4-9
詳細
2023 年 66 巻 1 号 p. 4-9
Low-temperature GaAs-based photoconductive antenna emits terahertz radiation when hit by femtosecond laser at 1.55 µm pump pulse. The nonlinear photocurrent at low laser power suggests a below band gap excitation due to two-step photon absorption mediated by mid-gap states. Using density functional theory with modified Becke-Johnson (mBJ) and local density approximation (LDA) for exchange-correlation, we confirm the mid-gap states and its origin. Due to broken inversion symmetry of GaAs, we introduced spin-orbit effects using projector augmented wave (PAW) method. Using the above methods, we were able to show that As antisite defect is the origin of the mid-gap state with energy level corresponding to 1.55 µm (～0.8 eV) sub-band gap excitation. In this article, we introduce our computationally-guided probing of such bulk defect in GaAs(110) surface, using Tersoff-Hamann theory-based STM simulation. The theoretically obtained STM images and the calculated local density of states are verified by experimental STM and STS.
