A U-grooved metal-semiconductor-metal photodetector (UMSM-PD) with an i-a-Si:H overlayer on a [100] P-type Si wafer

A metal-semiconductor-metal photodetector (MSMPD) with U-shaped interdigitated electrodes and an intrinsic hydrogenated amorphous silicon (i-a-Si:H) heterojunction, fabricated on a p-type [100] Si wafer, was studied. This Si UMSM-PD with a 70 nm i-a-Si:H overlayer, 0.9-μm-deep recessed electrodes, and a finger width and spacing of 3 μm, had a full-width at half-maximum (FWHM) of 50.8 ps, and a fall-time of 140 ps for its temporal response, a responsivity of 0.18 A/W, as measured with a 830-nm incident laser, a dark current density of 1.5 pA/μm² and an internal quantum efficiency of 27%. Its performance was much better than that of the conventional Si-based planar MSM-PD. The improved device characteristics were attributed to the U-shaped electrodes which resulted in a stronger lateral, electric field in the light absorption region of the photodetector.