Digital performance of high-speed MSM-HEMT monolithically integrated photoreceivers

In this work, we report the first multigigabit digital performance of a monolithic MSM-HEMT photoreceiver lattice matched to an InP substrate, with measured sensitivities at 5 Gb/s, 8 Gb/s, and 10 Gb/s of -16.9 dBm, -13.1 dBm, and -10.7 dBm, respectively for 1.55 μm light. The integration of MSM-PD and HEMT is done via a vertical integration scheme in which the HEMT and MSM layers are grown sequentially on a planar substrate in a single uninterrupted growth. The integration process features 0.2 μm gate length HEMTs, 0.5 μm MSM electrodes, Cr thin-film resistors, and SiN_x metal-insulator-metal capacitors, passivation, and photodetector antireflection coatings. The receiver circuit uses a low-noise three-stage transimpedance amplifier topology, with broadband output matching to 50 Ω. Two different amplifier designs were fabricated, resulting in systems with transimpedances ranging from 865 to 580 Ω and bandwidths from 7.2 to 12.4 GHz. In all cases, the frequency response is flat over the receiver bandwidth, with no evidence of peaking or ringing. Receiver output noise power spectral density measurements have also been performed, and the input-referred noise current determined for each receiver. The low-noise amplifier design results in input noise current densities of approximately 6.5 pA/Hz^1/2 for a transimpedance of 865 Ω and bandwidth of 7.2 GHz, and 8 pA/Hz^1/2 for a transimpedance of 580 Ω and bandwidth of 12.4 GHz