InP-based high sensitivity pin/HEMT/HBT monolithic integrated optoelectronic receiver

We report the first successful demonstration of a pin diode/HEMT/HBT monolithic integrated optoelectronic receiver lattice-matched on InP substrates for multi-gigabit long wavelength applications. Our approach utilizes a stacked single layer MBE growth of HEMTs and HBTs after which the HBT layers are patterned and selectively wet etched to expose the HEMT layers. The subsequent process steps feature HEMTs with 0.12 μm T-gates, HBTs with 2 μm emitter fingers, TaN thin-film resistors, SiN MIM capacitors, and photodetector antireflection coatings. The pin photodiodes comprise the base-collector junctions of the HBTs and thus are fabricated at the same time as the HBTs. The receiver circuit utilizes a high-gain three stage amplifier within the transimpedance feedback loop with a HEMT front end. The high f_T of the HEMT and the fully monolithic fabrication together with the photodiode and the HBTs result in a very small input node capacitance and low noise. A flat transimpedance gain of -6 kΩ with a bandwidth of 2.5 GHz is observed for supply voltages between 2.8-3.0 V. Circuit operation up to 7 Gb/s is obtained with an input PRBS length of 2⁷-1. At 10^-9 BER, sensitivities of -24.7, -21.2 and -18.5 dBm are observed for 2.5, 4 and 7 Gb/s operation respectively. At 2.5 Gb/s, a very good photocurrent sensitivity (ηP) of -27.9 dBm is measured