Fast micro-photodetector for shorter wavelengths on silicon-on-insulator structures

The thin active layer of a silicon-on-insulator (SOI) was utilized for the fabrication of small-size metal-semiconductor-metal (MSM) photodetcctors for blue or ultraviolet light, This is possible because silicon has strong optical absorption for the shorter wavelengths. Interdigitated electrodes in the detecting area of about 50 It in square showed a low dark current of less than 1 nA and a responsivity of 0.3 A/W at 488 nm wavelength, both at a bias of 2.5 V. The response to picosecond light pulses at 395 nm exhibited a full-width at half-maximum (FWHM) of about 100 ps in the bias range of 1-10 V. Samarium was employed for the Schottky contacts on the active layer of p-type silicon to suppress the dark current.