Stable gallium Arsenide MIS capacitors and MIS field effect transistors by (NH<inf>4</inf>)<inf>2</inf>S<inf>x</inf> treatment and hydrogenation using plasma deposited silicon nitride gate insulator

The beneficial effects of sulfur passivation of gallium Arsenide (GaAs) surface by (NH4)2 Sx chemical treatment and by hydrogenation of the insulator-GaAs interface using the plasma-enhanced chemical vapor-deposited (PECVD) silicon nitride gate dielectric film as the source of hydrogen are illustrated by fabricating Al/PECVD silicon nitride/n-GaAs MIS capacitors and metal insulator semiconductor field effect transistors (MISFET). Post metallization annealing (PMA) at temperatures in the range 450-550 °C is shown to be the key process for achieving midgap interface state density below 1011/cm2/eV and maximum incremental transconductance, which is about 75 % of the theoretical maximum limit. MIS capacitors are fabricated on (NH4)2Sx treated GaAs substrate using gate dielectrics such as PECVD SiO2 and silicon oxynitride to demonstrate that the PMA is less effective with these dielectrics because of their lower hydrogen content. The small signal a.c. transconductance, gms measurements on MISFETs fabricated using silicon nitride, have shown that the low-frequency degradation of gms is almost absent in the devices fabricated on (NH4)2 Sx-treated GaAs substrates and subjected to PMA. The drain current stability in these devices is demonstrated to be excellent, with an initial drift of only 2 % of the starting value. The dual role of silicon nitride layer, namely, protection against loss of sulfur and an excellent source of hydrogen for additional surface passivation along with sulfur is demonstrated by comparing the transconductance of MISFETs fabricated on GaAs substrates annealed without the nitride cap after the (NH4)2 Sx treatment.