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

Abstract

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 H 4 O H and ( N H 4 ) 2 S prior to atomic layer deposition (ALD) of Al 2 O 3 . In both cases, x-ray photoelectron spectroscopy data confirm the removal of As 2 O 3 ∕ As 2 O 6 upon Al 2 O 3 deposition. However, Ga–O bonds appear to incorporate in the final gate stack at the Al 2 O 3 ∕ Ga As interface. MOS capacitors exhibit a steep transition from accumulation to depletion as well as very low leakage current density indicating high quality of ALD - Al 2 O 3 . The midgap interface trap density was evaluated to be ( ∼ 3 – 5 ) × 10 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.