The surface velocity and the bulk lifetime of photo-excited free carriers in GaAs were measured using an optical-pump and THz-probe time-domain technique. By varying the pump laser photon energy from 1.56 to 4.15 eV, we observe that the surface velocity drops abruptly from 0.7×106 cm/s down to 0.2×106 cm/s at 2.5 eV, while the bulk lifetime remains almost constant. We tentatively explain this step-like behavior of the surface velocity vs the photon energy by a trapping of the free carriers at surface states, whose density of states shows a maximum at 2.5 eV.

中文翻译：

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通过紫外-可见泵浦探针太赫兹光谱测定 GaAs 的表面态相关载流子动力学

使用光泵和太赫兹探头时域技术测量了 GaAs 中光激发自由载流子的表面速度和体寿命。通过将泵浦激光光子能量从 1.56 eV 改变到 4.15 eV，我们观察到表面速度在 2.5 eV 时从 0.7×106 cm/s 突然下降到 0.2×106 cm/s，而体寿命几乎保持恒定。我们通过在表面态捕获自由载流子来尝试解释表面速度与光子能量的阶梯状行为，其态密度在 2.5 eV 处显示最大值。