High-Transconductance P-Channel Algaas/Gaas Hfet's with Low-Energy Beryllium and Fluorine Co-Implantation Self-Alignment

The fabrication and electrical characteristics of p-channel AlGaAs/GaAs heterostructure FET's with self-aligned p+ source-drain regions formed by low-energy co-implantation of Be and F are reported. The devices utilize a sidewall-assisted refractory gate process and are fabricated on an undoped AlGaAs/GaAs heterostructure grown by MOVPE. Compared with Be implantation alone, the co-implantation of F+ at 8 keV with 2 x 1014 ions/cm2 results in a 3 X increase in the post-anneal Be concentration near the surface for a Be + implantation at 15 keV with 4 x 1014 ions/cm2. It is shown that co-implantation permits a low source resistance to be obtained with shallow p+ source-drain regions. Although short-channel effects must be further reduced at small gate lengths, the electrical characteristics are otherwise excellent and show a 77-K transconductance as high as 207 mS/mm for a 0.5-μm gate length, representing the highest value reported for any GaAs-based p-FET.