Selective grown vertical GaAs FET´s with an insulator/metal/insulator gate structure

A vertical GaAs FET with sub-μm gate length has been grown using selective epitaxy. The gate structure of this device consists of an insulator/metal/insulator multilayer. The advantage of this structure is the reduction of the gate-source and gate-drain capacitances due to the relatively low dielectric constant of the insulator. In addition the insulator above the metal gate enables to use the selective epitaxy as a method for precise local growth control. In contrast to conventional overgrown Permeable Base Transistors voids and crystal defects above the gate structure are eliminated by selective epitaxy. Thus leading to a more reproducible electrical device performance. The DC IV characteristics shows a pentode like behaviour with a transconductance of 77 mS/mm for a channel width of 300 nm. We have measured a maximum frequency of oscillation of fmax = 7.5 GHz and a transit frequency of fT = 4.1GHz.