Laser diode action in the blue-green has been observed from (Zn,Cd)Se quantum wells within ZnSe/Zn(S,Se) p-n heterojunctions up to 250 K. Operation is reported for two different configurations for which the GaAs substrate serves either as the n- or p-type injecting contact. In pulsed operation, output powers exceeding 0.6 W have been measured in devices prepared on both n-type and p-type GaAs epitaxial buffer layers and substrates.

Microcavities which contain Zn-Cd-Se quantum wells as the resonant medium have been fabricated and tested at blue-green wavelengths. We see clear evidence of coupled-mode behavior at the n=1 heavy-hole exciton in both angle and temperature tuning experiments, with anticrossing (vacuum-Rabi) splittings approaching 20 rneV. The exciton-cavity interaction is consistent with predictions by theory in the strongcoupling regime, and illustrates the impact of the large oscillator strength available in II-VI compounds.Excitons in semiconductor microcavities is a contemporary subject as illustrated by several recent experimental reports that demonstrate the impact of enhanced coupling between extended electronic states in a crystalline solid and resonant electromagnetic waves.Important related theoretical activity has also emerged, ranging from classical reinterpretation of atomic physics pheonomena to full quantum description of the exciton-polariton states in a microcavity.Both experiment and theory have concentrated on the GaAs-based semiconductor heterostructures, in large part due to ready access by experiment to quality epitaxial material. Driven by the prospects of new compact blue-green diode lasers and other optoelectronic applications at short visible wavelengths, strong recent progress has been witnessed in wide-gap II-VI semiconductors, and a range of heterostructure designs is now available to test ideas associated with microcavity effects. One important and motivating difference, in this connection, between the GaAs-and ZnSebased quantum-well systems is that a considerably larger oscillator strength can be obtained in the latter case, as well as the condition where the exciton binding energy satisfies the inequality E )fttoLp kT (where htoLo is the optical phonon energy and kT is evaluated at room temperature).The robustness of such quasi-two-dimensional (2D) excitons in II-VI heterostructures is of relevance to the new bluegreen light emitters; here we demonstrate their impact in a microcavity environment in initial experiments. We use both angle tuning and temperature tuning to show coupled-mode behavior between the n=1 heavy-hole (HH) exciton in a (Zn, Cd)Se quantum well (QW) and the microcavity electromagnetic modes to obtain a quantitative measure of the normal mode (vacuum-Rabi) splitting. The splittings can reach values approaching 20 meV, and are clearly discernible in spite of a background line broadening on the order of 10 meV. Semiclassical theory provides very good agreement with the experiments in which transmission, reflectance, and photoluminescence have been used as optical probes. The II-VI semiconductor optical structure was based on a pseudomorphic (Zn, Cd)Se/Zn(S, Se)/(Zn, Mg)(S, Se) separate confinement heterostructure design, in which three uniformly strained 75-A-thick Zni, Cd"Se QW's provided the quasi-2D exciton confinement (xcd = 0.24), cladded by SiO /TiO DBR stack

The microstructure of a degraded II-VI blue-green laser diode based on the ZnCdSe/ZnSSe/ ZnMgSSe pseudomorphic separate confinement heterostructure has been examined by transmission electron microscopy. Triangular nonluminescent dark defects observed in the laser stripe region by electroluminescence microscopy have been identified to be dislocation networks developed at the quantum-well region. The dislocation networks have been observed to be nucleated at threading dislocations originating from pairs of V-shaped stacking faults which are nucleated at or near the II-VI/GaAs interface and extending into the n-ZnMgSSe lower cladding layer.

Spectroscopy on a single ZnSe quantum well characterized by a sharp exciton resonance ͑⌬Eϭ0.6 meV͒ shows how a gas of interacting excitonic molecules induces blue-green laser emission in an optically pumped heterostructure at cryogenic temperatures. Spectrally resolved four-wave-mixing experiments yield a molecular binding energy of 5 meV. However, the lasing occurs in an electron-hole density regime, where strong many-exciton interaction effects are evident.

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