HIGH-PERFORMANCE NONALLOYED PSEUDOMORPHIC HIGH-ELECTRON-MOBILITY TRANSISTORS

We have studied the InAs/GaAs strained layer superlattice (SLS) struct ures as non-alloyed contacts applied to pseudomorphic high electron mo bility transistors (PHEMTs) grown by the molecular beam epitaxy (MBE) system. Transmission line measurements with four point configurations showed that specific contact resistances between 6.6 x 10(-7) and 2.6 x 10(-6) Omega cm(2) were obtained for the as-grown devices, with a li near correlation coefficient of 0.997. D.c. measurements of the as-gro wn PHEMT with 1 mu m gate showed a transconductance of 240 ms mm(-1). Microwave measurements on the same device showed a cut-off frequency o f 19 GHz and a maximum power gain frequency of 42 GHz. These results a re comparable with those of devices with the conventional contact sche me. Meanwhile, since the non-alloying process maintains excellent surf ace morphology and sharp metal pad edges, AuGeNi type metals can be us ed in small dimension devices. In contrast, the conventionally alloyed devices showed rough surface morphology and zigzag edges, which may a ffect device processing and limit the usefulness of AuGeNi metal as th e ohmic contact in small dimension devices.