Threshold-voltage and hole-sheet-density model of quantum well Si/SiGe/Si p field effect transistor

Abstract

The low hole mobility restricts the application of Si complementary metal-oxide-semiconductor in high frequency fields. In this paper, the SiGe p-metal-oxide-semiconductor field-effect-transistor (PMOSFET) is studied. By numeric modeling and analysis, the vertical potential distribution of the device is obtained through solving one-dimensional Poisson equations, and the threshold-voltage model is established. The effects of Ge-profile, thickness of Si buffer layer, thickness of Si cap layer and substrate doping on the threshold-voltage are discussed. In SiGe layer, the quantization effect of the potential well in valence band is taken into account. When the gate voltage is large enough, the holes in SiGe channel layer will transit to the Si/SiO2 interface due to band bending and energy level splitting, causing the degradation of device performance. Thus, the hole-sheet-density model in quantum channel of SiGe PMOSFET is established, and the concept of the maximum operating gate voltage is proposed, moreover the channel saturation induced by gate voltage is calculated and analyzed. The results show that the threshold voltage and the maximal operating gate voltage are related to Ge-profile, and a proper increase of Ge-profile can extend the range of the operating gate voltage effectively.