We have studied the quasi-two-dimensional exciton in ZnSe/Zn x Mg 1Ϫx S y Se 1Ϫy ͑xϭ0.85, yϭ0.21͒ single quantum wells ͑SQWs͒ by photoluminescence and photoluminescence excitation spectroscopy. Self-consistent calculations of the peak energies for a series of SQWs give the conduction band discontinuity ⌬E c ϭ0.40⌬E g and the binding energy of the nϭ1 heavy-hole exciton E b ͑hh1͒ϭ22.1 meV for an 8 nm well width. We believe that the binding energy of the nϭ1 heavy-hole exciton is smaller than the LO phonon energy our samples resulting in a very large exciton-phonon interaction strength observed through the broadening of the exciton resonance with temperature.

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Effect of ion induced damage on carrier lifetimes in strained CdZnSe/ZnSe quantum wells

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The gain-spontaneous recombination characteristics have been calculated for a 40 Å Zn 0.8 Cd 0.2 Se-ZnSe quantum well including many body effects. We examine the effect of the inclusion of the Coulomb enhancement on the gain spectra and the gain-current relationship. We show that, in the absence of the Coulomb enhancement, the threshold current density of a 340 m 40 Å Zn 0.8 Cd 0.2 Se-ZnSe quantum well laser is underestimated by approximately 40% and the lasing wavelength overestimated by 4 nm. Our calculation of the scattering lifetime for the first electron-heavy hole transition gives a lifetime varying between 29 and 37 fs, and shows that the carrier-phonon scattering mechanism in II-VI quantum wells is more dominant than in III-V materials. We also comment on the effect the neglect of Coulomb enhancement has on the calculation of leakage currents in a laser at threshold. © 1995 American Institute of Physics.Recent advances in II-VI technology have led to the realisation of room temperature, cw blue-green laser diodes. [1][2][3] Problems with ohmic contacts, material quality and doping are actively being researched. Computer modelling of device structures is a useful tool in these studies. The effects of doping 4 and leakage current 5 have already been studied in this way. The foundation of such calculations is the determination of the material gain in the laser's active region as a function of the quasi Fermi levels or the carrier populations. Initial calculations of gain in II-VI quantum well structures used the free carrier approximation, 5-8 but the effect of the electron and hole Coulomb interaction has been shown to have a significant effect in the calculation of bulk II-VI material gain. 9 Commercial laser diodes are likely to use quantum wells due to their increased performance over bulk active region lasers. In this paper we illustrate the importance of the Coulombic interaction in the calculation of the material gain for a typical ZnCdSe-ZnSe quantum well structure. The enhancement for this II-VI structure is significantly larger than previously calculated for GaAs quantum wells. The intraband scattering rate used in the determination of the gain is calculated for both carrier-carrier and carrier-phonon scattering mechanisms. Our results show that the carrierphonon scattering contribution is considerably more significant in these II-VI structures than previously calculated for III-V quantum wells and therefore is an important inclusion in the calculation of gain.Many body effects manifest themselves in three main ways in the optical recombination spectra. [10][11][12] Optical transitions are broadened due to carrier scattering events. The band gap decreases ͑renormalisation͒ and the transition probability is enhanced due to the increased recombination resulting from the Coulomb attraction between electrons and holes. The room temperature gain characteristics of GaAs quantum wells have been calculated including many body effects. [10][11][12] These calculations show that band gap renormalisation and ...