Improved interface properties of an HfO₂ gate dielectric GaAs MOS device by using SiN_x as an interfacial passivation layer

A GaAs metal-oxide-semiconductor (MOS) capacitor with HfO₂ as gate dielectric and silicon nitride (SiN_x) as the interlayer (IL) is fabricated. Experimental results show that the sample with the SiN_x IL has an improved capacitance-voltage characteristic, lower leakage current density (0.785×10^-6 A/cm² at V_fb+1 V) and lower interface-state density (2.9×10¹² eV^-1·cm^-2) compared with other samples with N_2- or NH_3- plasma pretreatment. The influences of postdeposition annealing temperature on electrical properties are also investigated for the samples with SiN_x IL. The sample annealed at 600℃ exhibits better electrical properties than that annealed at 500℃, which is attributed to the suppression of native oxides, as confirmed by XPS analyses.