Ionization cross section of excitons due to scattering by free carriers in semiconducting quantum well structures

Abstract

We have extended our previous theoretical treatment of the scattering of excitons by free electrons and holes in a two-dimensional semiconducting quantum well system to obtain the ionization cross section of the exciton in these structures. The scattering cross section is calculated using the Born approximation for the scattering of the excitons by the free carriers and neglecting the effect of exchange. Results for the ionization cross section have been obtained both in the absence and presence of screening by the free carriers. The ionization cross section for the scattering of excitons by free carriers is comparable to the elastic scattering cross section when the heavy hole excitons are scattered by heavy holes and is much greater than the elastic scattering cross section for the case where the free carriers are electrons or light holes. The effect of screening by free carriers is to decrease the threshold energy at which the ionization of the exciton occurs but not to decrease the magnitude of the ionization cross section. Therefore, at temperatures where the free carriers have high enough energy to ionize the exciton, the contribution of the ionization cross section to the exciton linewidth should be very important.