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

A velocity-field study of several Si0.8Ge0.2/Si p-channel MOSFETs with self -aligned poly-Si gates, thick gate oxides and effective channel lengths ran ging from 1.5 to 8.5 mu m, was carried out at room temperature. Comprehensi ve two-dimensional simulations of devices using drift-diffusion (DD), and b ulk Monte Carlo calibrated hydrodynamic (HD) and energy transport (ET) mode ls have revealed enhanced high-field hole transport in strained-channel MOS FETs. 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 S i0.8Ge0.2 p-MOSFETs increases considerably as the gate length is decreased. The increase in short-channel samples is attributed to non-equilibrium tra nsport effects in the region near the source, resulting from higher mobilit y and longer relaxation times of holes in the strained SiGe layer. Our resu lts not only confirm the expected advantage of strained SiGe p-MOSFETs in l ow-field transport, but also indicate that this is accompanied by an early onset of velocity overshoot, which may be beneficial in aggressively scaled devices.