Silane–Ammonia Surface Passivation for Gallium Arsenide Surface-Channel n-MOSFETs

A novel surface passivation technology employing silane (SiH
₄
) and ammonia (NH
₃
) was demonstrated to realize high-quality metal-gate/high-
k
dielectric stack on GaAs. In addition to
ex

situ
cleaning/passivation and
in

situ
vacuum anneal to remove the native oxide on GaAs, the key improvements reported in this letter include the introduction of NH
₃
in a SiH
₄
passivation to form a SiN passivation layer that protects the GaAs surface from exposure to the oxidizing ambient during high-
k
dielectric deposition. Negligible As-O and Ga-O bonds were found. This passivation technology was integrated in a metal-organic chemical-vapor deposition tool. Inversion-type GaAs n-MOSFETs were fabricated with the SiH
₄
and NH
₃
passivation technology, showing good electrical characteristics with a peak effective mobility of 1920 cm
²
/V middots, an
I

_on
/
I

_off
ratio of ~ 10
⁵
, and a subthreshold swing of ~ 98 mV/dec, in surface-channel GaAs MOSFETs with a gate length of 2 mum.