CHARACTERISTICS OF NONALLOYED PSEUDOMORPHIC HIGH-ELECTRON-MOBILITY TRANSISTORS USING INAS INXGA1-XAS (X=-]0) ALYGA1-YAS (Y=0-]0.3) CONTACT STRUCTURES/

A molecular beam epitaxy InAs/InxGa1-xAs (x = 1 --> 0)/AlyGa1-yAs (y = 0 --> 0.3) heterojunction was used as an ohmic contact structure to t he GaAs-based pseudomorphic high electron mobility transistors (PHEMTs ). This nonalloyed PHEMT had a specific contact resistance r(c) of 1.0 5 x 10(-7) Omega . cm(2) and an extrinsic transconductance g(me) of 27 2 mS/mm for devices with 1 mu m gate-length, microwave measurements sh elved a current gain cut-off frequency f(t) of 22 GHz and a maximum os cillation frequency f(max) of 43 GHz. These results are comparable to our best conventional PHEMTs' alloyed at 450 degrees C and 2 min durat ion. Meanwhile, a small-signal equivalent circuit model of the nonallo yed PHEMT has also been demonstrated.