Depolarization and exciton-like shifts in modulation-doped single rectangular and diffusion-modified quantum wells under uniform electric fields

Energy levels in the modulation-doped single rectangular and diffusion-modi fied quantum wells Al0.3Ga0.7As/GaAs are obtained using the Kohn and Sham d ensity functional theory (DFT). The generalized DET which uses a screened e xchange potential in the local density approximation has been used to impro ve the accuracy of the energies and wavefunctions in these wells. The energ y difference between the first excited state and the ground state has been studied in the presence of combined photon and electric fields for two well s with well widths of 70 Angstrom and 100 Angstrom. The energy difference i s found to increase as a result of the depolarization and exciton-like shif ts when there is no external bias. Under the electric field the shift in th e energy difference decreases due to the vanishing of the exciton-like effe ct. The results obtained within the conventional Kohn and Sham DFT and with in the generalized DFT are found to be the same for the well with a width o f 100 Angstrom. However, the results obtained from these two schemes are fo und to be different when the well width is 70 Angstrom.