| InGaAs Metal-Semiconductor-Metal (MSM) photodetectors have been studied for high-speed optical communication applications because their low capacitance per unit area makes the MSM photodetectors suitable for high data rate operation. The low capacitance per unit area permits relatively large detection area devices, which gives larger tolerance for coupling to fibers. In this work, the MSM photodetectors with various InGaAs based epitaxial layer structures were fabricated and characterized in terms of dark current, responsivity, and bandwidth. A significant dark current reduction has been demonstrated for InGaAs MSM photodetectors with coplanar waveguides (CPW), and the dark current density of 0.56 pA/μm2 was achieved by eliminating the leakage current between transmission lines.; In order to improve the low responsivity of MSM photodetectors due to the shadowing effect, responsivity enhanced MSM photodetectors with asymmetric nanometer finger electrodes were proposed, designed, fabricated and tested. A responsivity of 0.74 A/W was achieved. In frequency response measurements at 1.55 μm wavelength, a 9 GHz 3-dB bandwidth was obtained. An impulse photoresponse measurement was also performed using a femto-second pulse laser at a wavelength of 820 nm, and a FWHM of 26 ps was achieved with a 50 x 50 μm 2 detection area device.; The optical receiver front end was demonstrated by integrating the MSM photodetector with a low noise preamplifier. A 3 dB bandwidth of 5.5 GHz was measured in the integrated optical receiver. |
