Ambipolar diffusion of high-density electrons and holes in Ge, Si, and GaAs: Many-body effects

Many-body effects are incorporated into a theory for the density dependence of the electron-hole ambipolar diffusion coefficient in semiconductors. Self-energy shifts of the free-carrier band edges lead to a band-gap gradient in the presence of a carrier-density gradient and therefore a diffusion coefficient which is less than that obtained from the independent-particle Boltzmann transport theory. The diffusion coefficient decreases with increasing carrier density until carrier degeneracy becomes important, after which the coefficient increases with density as in the independent-particle theory. The difference between the two theories is most apparent for high-effective-mass semiconductors and low carrier temperatures. Results are calculated for Ge, Si, and GaAs for common lattice and carrier temperatures of 100 and 300 K, with silicon showing the largest influence from many-body effects.