Polaron and bipolaron states in Si-inversion layers: Possible origins and effects

Abstract

We report results of a series of multiband tight-binding cluster calculations we have made to further uncover the origin and nature of the intrinsic interface states at the Si-SiO 2 interface as well as their effects on the n- and p-channel inversion layers. These results show that distortion (reconstruction) effects are important ingredients in the description of these states and this together with additional analysis indicates that threefold coordinated Si atoms at the Si-SiO 2 interface as well as strained Si-Si bonds on the oxide “side” on the interface can exist, as we have suggested earlier, in metastable configurations leading to e.g., device instabilities. A subgroup of these reconstructing interface states associated with weakly strained Si-Si bonds on the semiconductor side of the interface is identified and analyzed with emphasis on how such states can give rise to polaronic and bipolaronic effects in inversion layers and hence provide an additional basis for the Anderson-like negative U models previously employed by us in studying the low carrier density regime of this system.