Contents I. Introduction
Metal-semiconductor-metal photodetectors (MSM-PDs) are very attractive devices for optical fiber communication systems, high-speed chip-to-chip connections, and high-speed sampling [1]–[2]. The operation of an MSM-PD can be classified into two groups, according to whether its intrinsic speed is limited by recombination time or transit time. In the first group, a large number of recombination centers have to be introduced into the active area to shorten the carrier recombination time for high-speed operation at the expense of low sensitivity and less compatibility with field effect transistor integrated circuit fabrication. In the second group, small finger spacing is utilized to decrease the transit time and increase the device speed [3]. For MSM-PDs, the smaller the spacing, the shorter intrinsic response time is. Furthermore, for the recombination time-limited photodetectors, smaller finger spacing can increase the sensitivity. On the other hand, the smaller finger width, the less detector capacitance and the shorter external response time. However, the downsizing of the electrode spacing leads to a decreased active area resulting in sensitivity degradation.
