Metal-semiconductor-metal photodetectors (MSM-PDs) have gained much attention in recent years because of their ultrahigh speed and inherently low device capacitance. In this research project, interdigitated type MSM-PDs were fabricated on silicon and silicon-on-insulator (SOI) substrates using conventional UV lithography and lift-off technique. For Si MSM-PDs, we found that these detectors have fast response time and high magnitude of long current tails at a wavelength of 790 nm. These tails are attributed to the deep carrier generation because of the large penetration depth of silicon at this wavelength which limit the bandwidth of the detector. On the other hand, SOI MSM-PDs have shown to have much lower magnitude of current tail and thus dramatically increase their useful bandwidth....[ Read more ]

Metal-semiconductor-metal photodetectors (MSM-PDs) have gained much attention in recent years because of their ultrahigh speed and inherently low device capacitance. In this research project, interdigitated type MSM-PDs were fabricated on silicon and silicon-on-insulator (SOI) substrates using conventional UV lithography and lift-off technique. For Si MSM-PDs, we found that these detectors have fast response time and high magnitude of long current tails at a wavelength of 790 nm. These tails are attributed to the deep carrier generation because of the large penetration depth of silicon at this wavelength which limit the bandwidth of the detector. On the other hand, SOI MSM-PDs have shown to have much lower magnitude of current tail and thus dramatically increase their useful bandwidth. Impulse response measurement at a wavelength of 790 nm has shown that SO1 MSM-PD with 4pm finger spacing can achieve a response time as fast as 40 ps fulI width at half maximum (FWHM) and a 8.4 GHz electrical bandwidth which is limited by the system response. SOI MSM-PDs are therefore good candidates for front end photodetectors operated in the 0.8 - 0.87 μm wavelength region.

Due to the advancement of blue-green laser diode, future optical connection and devices will likely to be operated in the short wavelength range. Large bandgap II-VI materials such as Zinc Selenide (ZnSe) and Zinc Sulphur Telluride (ZnSTe) grown by molecular beam expitaxy (MBE) are also used as the semiconducting materials for our MSM-PDs. These detectors exhibit high speed ([is less than]80 ps FWHM) and have no observable current tail at excitation wavelength of 395 nm, this is due to the fast carrier recombination time and strong optical absorption at short wavelengths for these materials. The above observation make the high quality MBE grown II-VI semiconductors invaluable for high speed applications in the blue-green wavelength region.