The effect of N2 plasma damage on AlGaAs/InGaAs/GaAs high electron mobility transistors. I. DC characteristics

0.25 μm gate length AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistors were exposed to inductively coupled plasma (ICP) N₂ discharges at varied source power and rf chuck power. The plasma damage was characterized by evaluating device extrinsic transconductance and saturated drain–source current, as well as Schottky gate ideality factor and reverse breakdown voltage as a function of both ICP source power and rf chuck power. Auger and atomic force microscopy were also used to characterize the atomic ratio and roughness of plasma damaged surface, respectively. At a lower range of ICP source power (between 100 and 300 W) with a constant rf power of 10 W, the device performance was barely changed. But at higher ICP source power (greater than 400 W) and rf power (greater than 20 W), device characteristics including gate ideality factor, reverse breakdown voltage and saturated drain–source current were seriously degraded. In this plasma damage study, two device degradation mechanisms were identified. The first was ion bombardment induced lattice disorder that created generation–recombination centers and reduced the free carrier concentration. The second was preferential loss of As from GaAs surface and this also created deep level states, which gave rise to gate leakage current.