Effect of image charges on the optical absorption coefficient of a hydrogenic impurity in a surface quantum well

The present study investigates the effect of image charges on the first excited state binding energy and optical absorption coefficient (OAC), (linear, non-linear, and total), of a hydrogenic impurity in a surface quantum well (SQW) composed of vacuum/GaAs/Ga1-xAlxAs, using variational method, as a function of well width (L), Al concentration (x) and photon energy. A crossover in the plots (binding energy with and without image charges) was observed at L = 25 nm, which shows that the effect of image charges dominates in wide SQW. This L value, at which the binding energy shows a peak, is shifted to larger wellwidths due to the effect of image charges. For all x values, the donor binding energy increases, when image charges are included and the effect is more pronounced for low x values. As Al concentration increases the binding energy of the donor with image charges decreases. The presence of image charges decreases linear OAC, but increases non-linear OAC. The decrease of linear OAC is more than the increase of non-linear OAC and the combined effect is found to be a decrease in total OAC for all photon energies.