Two step doping channel FET with symmetric normally on and normally off characteristics

Abstract

An n −- GaAs n +- InGaAs two step doping channel FET prepared by MOCVD has been built for large input signals circuit applications. The thin InGaAs channel was heavily doped to increase current carrier density, resulting in a maximum current density of 930 mA/mm, and to improve the transconductance linearity, giving a very broad gate voltage range from 2.2 to −2.0 V. On the other hand, thick and lightly doped GaAs channel layer works as carrier confinement to reduce the gate leakage current and to enhance the breakdown voltage. A device with 2 × 100 μm 2 has yielded a maximum extrinsic transconductance of 230 mS/mm, a general gate-drain breakdown voltage of > 17 V and a f t = 15 GHz × μm. The performance of this device shows that two step doping channel FETs are very promising for high speed, high power and large input signal analog circuit applications.