Ultrafast All-Optical Terahertz Modulation with Sulfur-Passivated GaAs

With a surface-passivated GaAs, a performance-enhanced, ultrafast, all-optical spatial terahertz modulator was realized. The lower surface recombination rate and longer carrier lifetime induced by passivation render passivated-GaAs superior to pure-GaAs in modulation depth (MD) at a little sacrifice of response rate, eliminating its dependence on intensive laser. At low photodoping levels, the maximum of 1.6-times enhancement in MD was achieved. When the power increased to 60 mW, comparable MD of 94% to that in Si-based one at equivalent photodoping, and simultaneously ultrafast response of 69 MHz which is much faster than 100-kHz level by Si-based, was obtained. This performance-enhanced, ultrafast modulator is highly desired in actual situations and offers a viable avenue to breaking the compromise between MD and speed.