PHOTOLUMINESCENCE AND STIMULATED EMISSION OF THE DILUTED MAGNETIC SEMICONDUCTOR ZINC(1-X)MANGANESE(X)SELENIDE (POLYTYPES, LASER, BAND GAP, EPITAXIAL)
Abstract
A study of the optical properties of Zn(,1-x)Mn(,x)Se was carried out using photoluminescence and photoluminescence excitation spectroscopy. Bulk crystals were studied over the concentration range from x = 0.0 to x = 0.554 (x is the mole fraction of Mn). Zincblende epitaxial layers (100) grown by molecular beam epitaxy, with up to x = 0.61, have also been examined, as well as superlattice structures constructed of these materials. The energy of the band edge photoluminescence of bulk Zn(,1-x)Mn(,x)Se was found to be dependent on both Mn concentration and crystal structure. Scatter in the photoluminescence energy for 0.20 < x < 0.30 was observed and correlated with the polytype nature of the crystals, namely, those crystals for which the atomic layers were in a cubic environment had a smaller band gap than those for which the environment was hexagonal. Effects of the exchange interaction between Mn('2+) d-electrons and the band electrons have been observed. In particular, a decrease in the band gap at low x and an anomalous blue-shift at low T and high x have been observed and explained with this interaction. Superlattice structures constructed of alternating ZnSe and Zn(,1-x)Mn(,x)Se layers were examined. An enhanced quantum efficiency over that of ZnSe epilayers was found. A red-shift of the band edge photoluminescence in all the superlattices was observed and photoluminescence excitation spectra revealed a splitting between the n = 1 light and heavy hole subbands. The red-shift and valence subband splitting was found to be an increasing function of the amount of Mn in the Zn(,1-x)Mn(,x)Se superlattice layers. The results can be explained in terms in strain-induced effects, the strain being a consequence of the lattice mismatch between ZnSe and Zn(,1-x)Mn(,x)Se. Certain band edge features exhibited behavior (temperature, energy, and excitation density dependence) which is consistent with the predicted behavior of interface bound magnetic polarons. Also observed in these spectra was a region of low level luminescence which extended (TURN)75 meV above the dominant emission peak. This plateau region was also found to be present in ZnSe and Zn(,1-x)Mn(,x)Se epilayers. Possible models explaining the origin of the luminescence features are discussed. Stimulated emission in the blue was demonstrated and gain spectra were measured for three superlattices. Thresholds for stimulated emission were established to be lower than those seen earlier in bulk crystals. The regions of gain were determined to occur at energies below the band gap and polarization measurements confirmed that the gain occurred for transitions between conduction electrons and light holes. Lasing action was observed in the gain region at (TURN)453nm from LHe to 80K in specially prepared samples.
Degree
Ph.D.
Subject Area
Condensation
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