A U-GROOVED METAL-SEMICONDUCTOR-METAL PHOTODETECTOR (UMSM-PD) WITH ANI-A-SI-H OVERLAYER ON A [100]P-TYPE SI WAFER

A metal-semiconductor-metal photodetector (MSM-PD) with U-shaped inter digitated electrodes and an intrinsic hydrogenated amorphous silicon ( i-a-Si:H) heterojunction, fabricated on a p-type [100] Si wafer, was s tudied. This Si UMSM-PD with a 70 nm i-a-Si:H overlayer, 0.9-mu m-deep recessed electrodes, and a finger width and spacing of 3 mu m, had a full-width at half-maximum (FWHM) of 50.8 ps, and a fall-time of 140 p s for its temporal response, a responsivity of 0.18 A/W, as measured w ith a 830-nm incident laser, a dark current density of 1.5 pAl/mu m(2) , and an internal quantum efficiency of 27%. Its performance was much better than that of the conventional Si-based planar MSM-PD. The impro ved device characteristics were attributed to the U-shaped electrodes which resulted in a stronger lateral electric field in the light absor ption region of the photodetector.