Excitons with large binding energies in MgS/ZnSe/MgS and ZnMgS/ZnS/ZnMgS quantum wells

Abstract

The wide bandgap II-VI semiconductors have unique properties which allow the possibility of suppressing the exciton-phonon scattering up to room temperature in quantum well structures designed so that the exciton excitation E1s→2s>hνLO. In particular, magnetic field and temperature dependent measurements are used to study the exciton binding energies and to investigate the exciton-LO phonon scattering processes of high quality ZnSe quantum wells in MgS grown by MBE. The small inhomogeneous broadening of the exciton transitions in these samples allows the observation of higher excited exciton states. Due to the large difference in band gap between ZnSe and MgS the exciton binding energy in a 5 nm well is found to be 43.9 meV, which is the largest reported for this material system. The FWHM of the heavy hole absorption transitions measured as a function of temperature shows that the scattering of the excitons by the LO phonons is partially suppressed. These results are compared with ZnS quantum wells where the exciton g-values have been measured and the exciton binding energies have been deduced from the exciton diamagnetic shifts. The results show the possibility of suppressing exciton-LO phonon scattering in these structures.

Effect of Dielectric Mismatch on Exciton Binding Energy in ZnS/MgxZn1-xS Quantum Wells

“…The maximum heavy-and light-hole exciton binding energies calculated by considering the dielectric mismatch effect are smaller than those measured by Urbaszek et al for ZnS/Mg x Zn 1−x S SQWs at x = 0.19 [6]. The heavyhole (light-hole) exciton binding energy measured for a well width of 4 nm (3.5 nm) is considerably larger than that calculated by considering the dielectric mismatch effect.…”

“…The exciton binding energies are calculated as functions of the well width. For comparison, the heavy-and light-hole exciton binding energies measured for ZnS/Mg x Zn 1−x S SQWs when x = 0.19 [6] are also plotted. The difference in the alloy contents between the calculated and measured exciton binding energies is 0.01; therefore, we assume that the effect of quantum confinement on the excitons in ZnS/Mg x Zn 1−x S SQWs is the same at x = 0.19 and x = 0.2.…”

“…Therefore, ZnS-based QWs have potential applications in the fabrication of UV LDs. In particular, ZnS/MgZnS QWs have been experimentally studied for their use in the fabrication of UV optoelectronic devices [5][6][7]. Changes in the exciton binding energies with the well width have been measured for ZnS/MgZnS QWs.…”

“…Changes in the exciton binding energies with the well width have been measured for ZnS/MgZnS QWs. [5,6] The exciton binding energies in ZnS/MgZnS QWs calculated by considering and neglecting the Pollmann-Büttner (PB) potential have been reported [5,8]. The difference between the measured and calculated exciton binding energies in ZnS/ZnMgS QWs has been determined by Senger and Bajaj [8].…”

Effect of Exciton-Longitudinal Optical Phonon Interaction οn Exciton Binding Energies in ZnS/MgxBeyZn1-x-yS Quantum Wells

“…1a and b show the heavy-and light-hole exciton binding energies calculated by considering and ignoring the effect of the exciton-LO phonon interaction in ZnS/ Mg x Be y Zn 1−x−y S SQWs, respectively, for x = 0.14. For comparison of the theoretical results with the experimen-tal results, the heavy-and light-hole exciton binding energies measured for ZnS/Mg x Zn 1−x S SQWs at x = 0.19 [12] are also plotted. The bandgap discontinuity ∆E in ZnS/Mg x Be y Zn 1−x−y S SQWs for x = 0.14 is estimated to be 178.8 meV, whereas that in ZnS/Mg x Zn 1−x S SQWs for x = 0.19 is estimated to be 174.0 meV [7].…”