Impact of surface chemical treatment on capacitance-voltage characteristics of GaAs metal-oxide-semiconductor capacitors with Al2 O3 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 N H4 OH and (N H4) 2 S prior to atomic layer deposition (ALD) of Al2 O3. In both cases, x-ray photoelectron spectroscopy data confirm the removal of As2 O3 As2 O6 upon Al2 O3 deposition. However, Ga-O bonds appear to incorporate in the final gate stack at the Al2 O3 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- Al2 O3. The midgap interface trap density was evaluated to be (∼3-5) × 1011 cm2 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.