Narrow-gate In0.53Ga0.47As junctionfield-effect transistors as tunable resistors for long-wavelengthintegrated optical receivers

The fabrication of In_0.53Ga_0.47As junction field-effect transistors (JFETs) for use as active feedback resistors in integrated transimpedance photoreceivers is described. Transistors using both air-bridge and non-air-bridge technologies are described. Varying the gate-to-source voltage (V_GS) allows the output resistance to be tuned continuously between 3 and 40 kΩ with a drain-to-source shunt capacitance of less than 10 fF. The temperature coefficient of the output resistance is between -5 and -20 Ω/°C (for V_GS less than the pinch-off voltage). The combination of large resistance and low shunt capacitance can result in high receiver sensitivity without sacrificing amplifier dynamic range. The feedback FETs are fabricated adjacent to 1.8-μm gate JFETs with transconductances of 110 mS/mm and gate-to-source capacitances of 1.3 pF/mm