H plasma cleaning and a-Si passivation of GaAs for surface channel device applications

We discuss GaAs(001) cleaning and surface passivation for metal-oxide-semiconductor capacitors and field effect transistors fabricated with HfO2 as high-kappa gate oxide. An amorphous-Si passivating layer is deposited by molecular beam deposition on a 2x1 reconstructed GaAs surface cleaned using a remote rf H plasma. The H plasma effectively removes C contaminants from the surface, but a progressive Ga enrichment and the presence of Ga-O bonds are observed. The capacitance-voltage measurements on capacitors under peripheral illumination show inversion, which is an indication of a passivated interface. The D-it distribution as function of energy in the band gap is extracted by using the conductance technique at high and low temperatures and is reported for HfO2/a-Si gate stacks on H-cleaned GaAs. The observed D-it distribution is asymmetric. Values as low as 7x10(11) eV(-1) cm(-1) are found in the upper half of the band gap. One clear peak at 0.7 eV and a tail at 0.2 eV above the valence band maximum, which can be part of a second peak, are also observed. Transistor data confirm that a conducting channel is effectively opened at or very close to the GaAs surface.