A MODFET-based optoelectronic integrated circuit receiver for optical interconnects

The design, fabrication, and characterization of a 0.85-μm sensitive photoreceiver is described. The monolithically integrated optoelectronic receiver is based on pseudomorphic InGaAs on GaAs modulation-doped field-effect transistors (MODFETs) and metal-semiconductor-metal (MSM) photodetectors. High-performance quarter-micrometer MODFETs with f_t's of ~70 GHz are utilized in a two-stage transimpedance amplifier. An asymmetric and a symmetric amplifier design are compared. The symmetric design is found to provide the desired zero DC offset voltage for a variety of supply voltages. Excess MSM-detector dark current and low-frequency internal gain are greatly reduced through the use of a silicon passivation layer and/or AlGaAs cap layer. Receiver transimpedances between 100 and 5000 Ω are obtained by varying the bias on an active feedback resistor. The parasitic capacitances of this common-gate feedback FET are studied. A transimpedance amplifier bandwidth as high as 14 GHz and an overall photoreceiver bandwidth of 11 GHz are measured