140-GHz metal-semiconductor-metal photodetectors on silicon-on-insulator substrate with a scaled active layer

Metal-semiconductor-metal photodetectors with 100-nm finger spacing and width on a silicon-on-insulator substrate that has a scaled active layer were fabricated and characterized using electro-optic sampling. The unique device structure cuts off carriers generated deep inside the semiconductor substrate, resulting in a measured response time of 3.2 ps and a bandwidth of 140 GHz. Furthermore, the detector structure makes the detector’s speed independent of the light penetration depth and thus the light wavelength. Good metal-semiconductor Schottky contact and low detector dark current have been achieved.