GaAs FET Device Fabrication and Ion Implantation Technology (Microwave III-V Compound Semiconductors).

Abstract : Microwave Schottky barrier FETs and ion implantation have been selected to provide a bench mark technology for evaluation of III-V compound semiconductor materials grown at NRL and elsewhere. FETs used here employ a nominal one micron gate length and are processed by a combination of conventional contact photolithography and liftoff techniques. Ion implantation studies have centered about creating doping profiles suitable for active layers in GaAs and InP FETs using semi-insulation (SI) substrates. These substrates are previously qualified by capping with plasma deposited Si3N4 and annealing between 800 C and 850 C for 15-30 minutes (GaAs) or 700 C-750 C for 15 minutes (InP). Samples which show surface conversion after the anneal are rejected. NRL has demonstrated proficiency in being able to implant, cap and anneal both GaAs and InP SI substrates. GaAs FETs were fabricated on ion implanted NRL SI substrates (unintentionally doped) and on commercially supplied Cr doped SI GaAs with epitaxial channel regions. At 8 GHz the noise figure ranged from 3.4 dB - 3.8 dB with 6-8 dB associated gain for these devices. Differences in microwave performance between ion implanted and epitaxial FET was correlated to differences in mobility and and velocity profiles obtained from FAT FET test structures and actual microwave FET devices, respectively. Results suggest the need for improvement in FET process technology and capping technology. (Author)