Surface-modified semiconductors show enormous potential for opto-terahertz (THz) spatial modulation due to their enhanced modulation depth (MD) along with their inherent broad bandwidth. Taking full advantage of the surface modification, a performance-enhanced, all-optical, fast switchable THz modulator was achieved here based on the surface-passivated GaAs wafer. With a decreased surface recombination rate and prolonged carrier lifetime induced by passivation, S-passivated GaAs was demonstrated as a viable candidate to enhance THz modulation performance in MD, especially at low photodoping levels. Despite a degraded modulation rate owing to the longer carrier lifetime, this passivated GaAs modulator simultaneously realizes a fast modulation at a 69-MHz speed and as high an MD as $\sim 94\%$ in a spectral wideband of 0.2–1.2 THz. The results demonstrated a new strategy to alleviate the tradeoff between high MD and speed in contrast to bare surfaces or heterogeneous films/unusual geometry on semiconductors including Si, Ge, and GaAs.

中文翻译：

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通过表面钝化增强基于 GaAs 的快速太赫兹调制器的性能

由于其增强的调制深度 (MD) 及其固有的宽带宽，表面改性半导体在光太赫兹 (THz) 空间调制方面显示出巨大的潜力。充分利用表面改性，基于表面钝化的 GaAs 晶片实现了性能增强、全光、快速可切换的太赫兹调制器。由于钝化导致表面复合率降低和载流子寿命延长，S 钝化 GaAs 被证明是增强 MD 中太赫兹调制性能的可行候选者，尤其是在低光掺杂水平下。尽管由于更长的载流子寿命而降低了调制率，但这种钝化的 GaAs 调制器同时实现了 69 MHz 速度的快速调制和高达$～94\%$在 0.2-1.2 THz 的频谱宽带中。结果表明，与半导体（包括 Si、Ge 和 GaAs）上的裸表面或异质薄膜/不寻常几何形状相比，该结果展示了一种新策略，可以减轻高 MD 和速度之间的权衡。