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

A novel surface passivation technology employing silane (SiH₄) and ammonia (NH₃) 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 NH₃ in a SiH₄ 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 SiH₄ and NH₃ passivation technology, showing good electrical characteristics with a peak effective mobility of 1920 cm²/V middots, an I _on/I _off ratio of ~ 10⁵, and a subthreshold swing of ~ 98 mV/dec, in surface-channel GaAs MOSFETs with a gate length of 2 mum.