InAlAs/InGaAs/InP MODFET's with uniform threshold voltage obtained by selective wet gate recess

Excellent uniformity in the threshold voltage, transconductance, and current-gain cutoff frequency of InAlAs/InGaAs/InP MODFETs has been achieved using a selective wet gate recess process. An etch rate ratio of 25 was achieved for InGaAs over InAlAs using a 1:1 citric acid:H/sub 2/O/sub 2/ solution. By using this solution for gate recessing, the authors have achieved a threshold voltage standard deviation of 15 mV and a transconductance standard deviation of 15 mS/mm for devices across a quarter of a 2-in-diameter wafer. The average threshold voltage, transconductance, and current-gain cutoff frequency of 1.0- mu m gate-length devices were -234 mV, 355 mS/mm, and 32 GHz, respectively.<
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