Engineered Silicon for Efficient mm-Wave and THz Modulators

Optical excitation is a useful means by which to modulate mm-wave and THz radiation. However, most photoconductive materials require intense photoexcitation to provide sufficient modulation, often relying on hugely expensive light sources such as amplified femtosecond lasers. Here we show that, through surface passivation, one can engineer silicon to yield a highly sensitive photomodulator with an efficiency that is three orders of magnitude greater than “off-the-shelf” wafers. Moreover, by using a layer of indium tin oxide to create a cavity with an un-doped silicon wafer, the modulation is increased by up to a factor of 7 for relatively low illumination powers, without compromising switching time or spatial resolution.