Energetic shift of cold and hot excitons in (Cd, Mn)Te/(Cd, Mg)Te quantum wells

Optical spectra of 80 Å, 100 Å, 120 Å, and 140 Å (Cd, Mn)Te quantum wells separated by the (Cd, Mg)Te barriers were measured by means of the pulsed pump-probe method with circular polarization resolution. The energy shifts of a heavy-hole neutral exciton X_e1hh1 were recorded as a function of excitation energy for different excitation beam powers at zero time delay between pulse and probe. Photoluminescence excitation spectra for different pump mean power were also measured. The energy shifts of the X_e1hh1 exciton to higher values were observed when the excitation energy approached the resonant value from the lower energy side. The maximum of the shift was at resonance conditions. Beyond the resonance the shift weakens very rapidly despite still rising density of excitons. Creation of hot excitons—above the resonance; causes weakening of interaction between excitons. Theoretical calculations predicts also weakening of energy shift with rising temperature of created e-h pairs.