THE FABRICATION OF BACK-GATED HIGH ELECTRON-MOBILITY TRANSISTORS - A NOVEL-APPROACH USING MBE REGROWTH ON AN INSITU ION-BEAM PATTERNED EPILAYER

We present a new method for the fabrication of GaAs/AlGaAs back-gated high electron mobility transistors (HEMTs) involving MBE regrowth on an in situ ion beam patterned epilayer. In our structures the ohmic contacts to the two-dimensional electron gas (2DEG) are arranged to lie above regions where the back-gate has selectively been rendered highly resistive by 10 keV Ga ion implantation. This removes the need for shallow ohmic contacts, which are often difficult to form when milli-kelvin operation is required, and consequently high device yields with improved gate leakage characteristics are obtained. We show that this technique can be used to reduce the separation between the back-gate and the 2DEG from 1.38 to 0.22 mum, whilst maintaining successful control of the 2DEG carrier concentration. Further, despite the growth interruption required for ion implantation, no degradation of the sample quality is observed.