Indication of velocity overshoot in strained Si0.8Ge0.2p-channel MOSFETs

A velocity-field study of several Si 0.8 Ge 0.2 /Si p-channel MOSFETs with self-aligned poly-Si gates, thick gate oxides and effective channel lengths ranging from 1.5 to 8.5 µm, was carried out at room temperature. Comprehensive two-dimensional simulations of devices using drift-diffusion (DD), and bulk Monte Carlo calibrated hydrodynamic (HD) and energy transport (ET) models have revealed enhanced high-field hole transport in strained-channel MOSFETs. A close agreement is obtained between higher-level (HD/ET) models and DD model with calibrated high-field mobility parameters. It is found that the relatively low value of extracted saturation velocity in long-channel Si 0.8 Ge 0.2 p-MOSFETs increases considerably as the gate length is decreased. The increase in short-channel samples is attributed to non-equilibrium transport effects in the region near the source, resulting from higher mobility and longer relaxation times of holes in the strained SiGe layer. Our results not only confirm the expected advantage of strained SiGe p-MOSFETs in low-field transport, but also indicate that this is accompanied by an early onset of velocity overshoot, which may be beneficial in aggressively scaled devices.