PHOTOLUMINESCENCE STUDIES OF THE DILUTED MAGNETIC SEMICONDUCTORS CADMIUM MANGANESE TELLURIDE AND CADMIUM MANGANESE SELENIDE
Abstract
Photoluminescence (PL) and excitation measurements are carried out on the ternary semiconducting alloys Cd(,1-x)Mn(,x)Te and Cd(,1-x)Mn(,x)Se (x in mole fraction). The concentration and temperature dependence of PL bands located at (TURN) 2.0 eV and (TURN) 1.2 eV for CdMnTe and (TURN) 2.13 eV and (TURN) 1.35 eV for CdMnSe are presented. Similarities in the behaviors of the bands suggest that they are related predominantly to Mn('2+) intraion transitions. The 2.0 eV PL band in Cd(,1-x)Mn(,x)Te is investigated over the concentration range 0.4 (LESSTHEQ) x (LESSTHEQ) 0.7 and over the temperature range 1.8K (LESSTHEQ) T (LESSTHEQ) 220K. The emission is ascribed to the ('4)T(,1)(('4)G) (--->) ('6)A(,1)(('6)S) internal transitions of the Mn('2+) ions. A phonon energy of (H/2PI)(omega) = 53 (+OR-) 16 cm('-1) and a Huang-Rhys factor of S' = 26 (+OR-) 2 is obtained using a linear configurational coordinate model. Additionally, a value of inhomogeneous broadening, H(,in) = 80meV (645 cm('-1)), is found from the analysis. The inhomogeneous broadening is seen to be related to a disorder-induced distribution of ('4)T(,1) emitting states. Such a distribution of excited states is used to discuss concentration and temperature dependence of the PL line shift. Excitation spectra show the onset of the ('6)A(,1) (--->) ('4)T(,1) transition at x (GREATERTHEQ) 0.4 at an exciting photon energy of (TURN) 2.2 eV. For samples with x > 0.6, the ('6)A(,1) (--->) ('4)T(,2) transition at (TURN) 2.55 eV is revealed as well. A high energy cutoff in excitation is attributed to intrinsic absorption which competes strongly with the Mn('2+) absorption. Details of this behavior are reproduced by a model which assumes separate Urbach tails for the Mn('2+) and intrinsic absorptions. PL and excitation studies are carried out on the CdMnTe 1.2 eV emission. The excitation spectra are found to be similar to those of the 2.0 eV PL band. Furthermore, when the temperature dependence of the intensities of the 2.0 eV and 1.2 eV PL bands are compared, it is observed that the two emissions appear to be thermally related. A thermal barrier model is presented which describes the results. The 1.35 eV and 2.13 eV PL bands in Cd(,1-x)Mn(,x)Se are studied for 0.3 (LESSTHEQ) x (LESSTHEQ) 0.45 and are found to exhibit behavior similar to their counterparts in CdMnTe. The presence of these two similar pairs of PL bands is explained in terms of a static Jahn-Teller effect acting at nearly tetrahedrally coordinated Mn('2+) ions.
Degree
Ph.D.
Subject Area
Condensation
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