Narrow-gate In/sub 0.53/Ga/sub 0.47/As junction field-effect transistors as tunable resistors for long-wavelength integrated optical receivers

The fabrication of In/sub 0.53/Ga/sub 0.47/As 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/sub GS/) allows the output resistance to be tuned continuously between 3 and 40 k Omega with a drain-to-source shunt capacitance of less than 10 fF. The temperature coefficient of the output resistance is between -5 and -20 Omega / degrees C (for V/sub 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- mu m gate JFETs with transconductances of 110 mS/mm and gate-to-source capacitances of 1.3 pF/mm.<
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