Polarization dependence of the response of micrometer and submicrometer InGaAs metal-semiconductor-metal photodetectors

The external quantum efficiency of interdigitated InGaAs metal-semiconductor-metal (MSM) photodetectors with micrometer and submicrometer electrode feature sizes are investigated under front illumination with 1.3-μm light polarized perpendicular (TM) and parallel (TE) to the direction of the finger electrodes. As a result of the lamellar grating structure of the electrode pattern, the external quantum efficiency is observed to be considerably larger for TM polarization when the magnitude of the electrode period is reduced to that of the optical wavelength of the incident light. For devices with electrode spacing and width as small as 0.3 μm, the efficiency for TM polarized light exceeds that for TE excitation by about a factor of 6. The temporal waveform of the response to picosecond optical pulses is found to be independent of the state of polarization and its amplitude scales with the continuous-wave (CW) quantum efficiency. For applications of MSM photodetectors, which require high-speed and polarization-insensitive operation, alternative electrode patterns based on circularly shaped finger electrodes are proposed and analyzed with respect to their electrical circuit properties.