Application of focused ion beam implantation to produce gallium arsenide metal semiconductor field-effect transistors with a novel doping profile

We report the fabrication and performance of a new gallium arsenide (GaAs) metal semiconductor field-effect transistor (MESFET) device. The new device combines the concept of step-doping, where the doping of the channel is changed in a step, from high towards the source to low towards the drain, of the MESFET channels with that using a buried p-layer under the channel. Focused ion beams (FIBs) of silicon (Si) and beryllium (Be) were used, respectively, to implant the n-layer for the stepped channel and the p-layer at the channel substrate interface. A range of Be co-implantation doses and energies were studied for 150 keV channel implantation. The Be co-implanted layer improves the transconductance and pinch-off voltage of the devices by increasing the abruptness of the channel layer and reducing the substrate current. The available power from a step-doped device is high compared to uniform-channel devices with either low or high dopant concentration. (author)