Impact of the silicon-nitride passivation film thickness on the characteristics of InAlAs/InGaAs InP-based HEMTs

Abstract

In this research, the DC and RF characteristics for our own InAlAs/InGaAs InP-based high-electron-mobility transistors (HEMTs) with 0-nm, 50-nm, and 200-nm silicon-nitride (Si3N4) passivation films have been investigated comprehensively and systematically. With increasing Si3N4 passivation film thickness, the device exhibits an apparent improvement in the output conductance and a distinct drift of the pinch-off voltage toward a positive value. Especially, the device passivated by using a 50-nm Si3N4 film demonstrates the highest extrinsic transconductance and channel current. The appeared changes of the DC properties can be interpreted as due to the passivationinduced positively-charged surface state increasing the sheet carrier density with the carrier mobility and parasitic resistance of device being deteriorated by long-time high-stress-intensity ion bombardment. Additionally, the degradations of the current-gain cutoff frequency (f T) and maximum oscillation frequency (f max) can be attributed to the drastically-increased parasitic capacitance and resistance induced by the passivation process. This work will be of great importance in fabricating InP HEMTs with high performances.