Hetero-emitter-like characteristics of phosphorus doped polysilicon emitter transistors. Part II: band deformation due to residual stress in the polysilicon emitter

For part I see ibid., vol.42, no.3, pp.419-26 (1995). The purpose of this paper is to clarify the cause of the hetero-emitter-like characteristics reported for bipolar transistors having a poly-Si emitter which is crystallized from an in-situ phosphorus-doped amorphous Si layer. It has been clarified by X-ray diffraction measurements that there is large lattice deformation at the interface of the poly-Si layers with the Si substrate. This lattice deformation corresponds to tensile stress of about 1.0 GPa. We have calculated the band structure at the interface by the deformation potential theory using the measured lattice deformation. The calculated band structure mostly coincides with that determined electrically in our previous paper, part I of this series. Moreover, the hetero-emitter-like characteristics are found to be stronger in the cases of larger residual stress. We therefore conclude that the origin of the hetero-emitter-like characteristics is the band discontinuity at the interface which is produced by the band deformation due to the residual stress in the poly-Si layer