An Al.5Ga.5As gate heterojunction microwave FET

DC, small signal microwave, and large signal switching performance of normally-ON heterojunction Al.5Ga.5As gate, GaAs FETs (N-ON HJFET) with submicron gate dimensions are reported. Ge-doped p-type Al.5Ga.5As and p⁺-type GaAs layers are grown by liquid phase epitaxy (LPE) on an n-type active channel layer grown by vapor phase epitaxy (VPE). The submicron gate structure is obtained by selectively etching first the GaAs layer and later the Al.5Ga.5As layer. The resulting GaAs overhang is used to self align the source and the drain with respect to the gate. Devices with about 0.6 micron gate length exhibit a maximum available power gain (MAG) of about 9.5 dB at 8 GHz. Large signal pulse measurements indicate an intrinsic propagation delay of 20 psec.