Impact of Sulfur Passivation on Carrier Transport Properties of In 0.7 Ga 0.3 As Quantum-Well MOSFETs

We investigated the impact of a sulfur passivation (S-passivation) process step on carrier transport properties of surface-channel In0.7Ga0.3As quantum-well (QW) Metal-Oxide-Semiconductor Field-Effect-Transistors (MOSFETs) with source/drain (S/D) regrowth contacts. To do so, we fabricated long-channel In0.7Ga0.3As QW MOSFETs with and without (NH4)2S treatment prior to a deposition of Al2O3/HfO2 = 1-nm/3-nm by atomic-layer-deposition (ALD). The devices with S-passivation exhibited a lower value of subthreshold-swing (S) = 74 mV/decade and more positive shift in the threshold voltage ( $\text{V}_{\mathrm{ T}}$ ) than those without S-passivation. From the perspective of carrier transport, S-passivated devices displayed excellent effective mobility ( $\mu _{eff}$ ) in excess of 6,300 cm2/ $\text{V}\cdot \text{s}$ at 300 K. It turned out that the improvement of $\mu _{eff}$ was attributed to reduced Coulombic and surface-roughness scatterings. Using a conductance method, a fairly small value of interface trap density $({\mathrm{ D}}_{\mathrm{ it}}) = 1.56 \times 10^{12}$ cm $^{-2}$ eV $^{-1}$ was obtained for the devices with S-passivation, which was effective in mitigating the Coulombic scattering at the interface between the high-k dielectric layer and the In0.7Ga0.3As surface-channel layer.