Optical Phase Modulators Based on Reverse-Biased III-V/Si Hybrid Metal-Oxide-Semiconductor Capacitors

We present an efficient optical modulator with reverse-biased III-V/Si hybrid metal-oxide-semiconductor (MOS) optical phase shifters. By applying a reverse bias on a III-V/Si hybrid MOS capacitor, we found that the Franz-Keldysh effect and carrier depletion contribute to an efficient optical phase modulation. Compared with forward-biased MOS-type optical modulators based on carrier accumulation, the reverse-biased III-V/Si hybrid MOS capacitor shows a small depletion capacitance, which improves the trade-off relationship between modulation bandwidth and energy consumption. We have numerically analyzed the proposed optical modulator in terms of wavelength detuning as well as doping concentrations in the Si and III-V layers. After carefully tuning the doping concentration in Si and III-V layers, a small $V_{\pi }L$ of 0.17 Vcm with a modulation bandwidth of above 200 GHz was predicted. We also experimentally demonstrated the proposed optical modulator that exhibited a $V_{\pi }L$ of 0.12 Vcm. The reverse-biased III-V/Si hybrid MOS optical modulator showed a capacitance half that of the forward-biased III-V/Si hybrid MOS optical modulator with a comparable modulation efficiency, resulting in the enhancement of the modulation bandwidth by a factor of two with the energy per bit reduced by half.