Integration of Nanometer-Thick 1T-TaS₂ Films with Silicon for an Optically Driven Wide-Band Terahertz Modulator

The amplitude of terahertz (THz) waves is modulated optically by a pumping laser source, and the effect of optical power on modulation depth is systematically investigated in this work. The reported THz modulator is based on a conducting transition metal dichalcogenide (TMD), that is, a nanometer-thick thin film of tantalum disulfide (TaS2) grown on a high-resistivity silicon (Si) substrate. The Raman spectrum confirms the formation of the 1T phase of TaS2. Modulation depths of 69.3 and 46.8% have been achieved at 0.1 THz and 0.9 THz frequency, respectively, under a low pumping power of 1 W/cm2. A constant higher modulation depth in the wide frequency range reveals the broadband response of the THz modulator. Under the same conditions, the modulation increased twice as compared to bare Si after annealing at 300 °C in the presence of air. Furthermore, numerical analysis based on the finite-difference time domain shows that a greater number of photogenerated charge carriers are present near the interface of Si and TaS2, which leads to enhancement in modulation. The utilization of 1T-TaS2 imparts potential to these TMDs in the wide THz frequency range and unfolds the possibilities for their use in THz imaging, wireless communication, and detection processes.