MODELING OF ELECTRON-HOLE SCATTERING IN SEMICONDUCTOR-DEVICES

It is generally assumed in device modeling that the effects of electro n-hole scattering can be fully accounted for by a suitable reduction i n the electron and hole mobilities with injection level, without modif ying the semiconductor device equations themselves. Physical considera tions indicate that this is not the case, and that electron-hole colli sions introduce a direct coupling between the electron and hole curren ts. This is analyzed from first principles, and the results of a Boltz mann calculation are described. The key result is that the impact of a n electron-hole scattering event depends upon the relative drift veloc ity between electrons and holes. In low injection, the effective minor ity-carrier diffusion mobility cannot be assumed to be identical to ma jority-carrier mobilities or to minority-carrier drift mobilities. In high injection, a reduction in the conductivity mobility does not impl y a reduction in the ambipolar diffusion constant. The complete treatm ent in high-injection differs significantly from the conventional trea tment in any power device where ambipolar diffusion length is importan t. This is analyzed for p-i-n diodes.