Characteristics of MSM photodetectors with trench electrodes on P-type Si wafer

U-grooved metal-semiconductor-metal photodetectors (UMSM-PD's) having various trench depths of interdigitated electrodes and an intrinsic hydrogenated amorphous silicon (i-a-Si:H) to c-Si heterojunction have been fabricated successfully on a p-type [100] Si wafer, The U-grooved structures on c-Si were achieved with a simple orientation-dependent etching (ODE) process. Some important characteristics of the obtained UMSM-PD's are presented and discussed. An UMSM-PD with a 70 nm i-a-Si:H overlayer, 1.45 mu m-deep recessed electrodes, and 3 mu m finger width and spacing, had a full width at half maximum (FWHM) of 50.6 ps and a fall-time of 132 ps for its temporal response under a bias of 15 V. The significant improvements of transient response for UMSM-PD, as compared to the conventional one, were attributed to the trench electrodes resulted in a stronger lateral electric field in the light absorption region of photodetector. At a bias of 20 V, this UMSM-PD had a responsivity of 0.25 A/W as measured with an 0.83-mu m incident semiconductor laser, a high photo/dark current ratio about 2000, and an internal quantum efficiency of 36%. This high photo/dark current ratio would be due to the additional i-a-Si:H overlayer on Si wafer. These mentioned performances were much better than those of the conventional Si-based planar MSM-PD.