High performance InPInGaAs-BASED MSM photodetector operating at 1.3-1.5 μm

We report the fabrication and characteristics of high-speed, low-capacitance, high-responsivity metal-semiconductor-metal photodetectors (MSMPDs). These detectors are based on an InGaAs absorption layer incorporating an InP barrier enhancement layer grown on a semi-insulating InP substrate by gas-source molecular beam epitaxy (GSMBE). All epitaxial layers were not intentionally doped. The interdigitated metal electrodes, with 2 μm finger width and spacing, were formed using a Pt/Ni/Au contact film on a 50 μm by 50 μm active area. A very low dark current of 200–400 nA was observed below the bias voltage of 10 V. The devices have a capacitance of less than 2 pF. Photoresponsivities were measured under various illumination powers. Recorded typical responsivity is 0.5-0.6 A W−1. The highest responsivity of 0.78 A W−1 was observed at 10 V bias, which corresponds to an external quantum efficiency of 0.74. High-speed performance of the detectors was assessed using an electro-optic sampling (EOS) technique. The impulse response to a short optical pulse of 100 fs was recorded to assess the high speed performance. The output pulse has a rise time of 3.4–5 ps, a fall time of 8.5–11 ps, and an 8.6–11 ps full-width at half-maximum (FWHM). This corresponds to an 8–10 GHz 3 dB bandwidth, which is shown to be comparable with high-frequency measurements.