Impact of surface chemical treatment on capacitance-voltage characteristics of GaAs metal-oxide-semiconductor capacitors with Al2O3 gate dielectric

The authors examine the impact of two different chemical surface treatment methods on capacitance-voltage characteristics of GaAs metal-oxide-semiconductor (MOS) capacitors using NH4OH and (NH4)(2)S prior to atomic layer deposition (ALD) of Al2O3. In both cases, x-ray photoelectron spectroscopy data confirm the removal of As2O3/As2O6 upon Al2O3 deposition. However, Ga-O bonds appear to incorporate in the final gate stack at the Al2O3/GaAs interface. MOS capacitors exhibit a steep transition from accumulation to depletion as well as very low leakage current density indicating high quality of ALD-Al2O3. The midgap interface trap density was evaluated to be (similar to 3-5)x10(11)/cm(2) eV using the Terman method. In addition, quasistatic capacitance-voltage (C-V) measurement confirms the formation of true inversion layer in GaAs using both chemical treatment protocols. However, sulfur-passivated GaAs demonstrates better frequency dispersion behavior and slightly smaller capacitance equivalent thickness than hydroxylated GaAs. A statistical study substantiates the reproducibility of these results. (c) 2007 American Institute of Physics.