GaAs metal–oxide–semiconductor device with titanium dioxide as dielectric layer: effect of oxide thickness on the device performance

Abstract

GaAs-based metal–oxide–semiconductor devices were fabricated with titanium dioxide (TiO₂) as an oxide layer having three different thicknesses of 33, 54 and 71 nm. The phase purity of TiO₂ was confirmed by Raman spectroscopy. Sulfur passivation on GaAs surface prior to TiO₂ deposition was proposed to suppress poor native oxide formation on GaAs. Frequency-dependent studies on the capacitance–voltage were made in the frequency range 10 kHz–1 MHz. It was found that within this frequency range dispersion of the oxide capacitance was 4.9% per decade. Electrical measurements exhibited low leakage current, a dielectric constant of ≈27 and an interface trap density (D _it) of ∼10¹¹ cm⁻² eV⁻¹. Two orders of magnitude reduction in current density were observed as the temperature went down from 290 to 100 K. Flatband voltage (V _FB), dielectric loss tangent (tan φ) and ac conductivity (σ_ac) were determined from the capacitance–voltage (C–V) and conductance–voltage (G _P/ω–V) characteristics as a function of oxide thickness.