OPTICAL ABSORPTION STUDIES OF THE DILUTED MAGNETIC SEMICONDUCTORS ZINC(1-X)MANGANESE(X)TELLURIUM, CADMIUM(1-X)MANGANESE(X)SELENIUM, AND ZINC(1-X)MANGANESE(X)SELENIUM
Abstract
Optical absorption measurements were carried out on the dilute magnetic semiconductors Zn(,1-x)Mn(,x)Te, Cd(,1-x)Mn(,x)Se, and Zn(,1-x)Mn(,x)Se: high manganese concentration was emphasized. For photon energies in the vicinity of the intrinsic absorption, sample thicknesses down to (TURN)10 (mu) were required. Results were obtained at room temperature, liquid nitrogen, and liquid helium. Samples of the zincblende crystal Zn(,1-x)Mn(,x)Te were studied at compositions x (TURN) 0.1, x (TURN) 0.5, and x (TURN) 0.6. Three absorption bands with maxima at (TURN)2.33, (TURN)2.40, and (TURN)2.605 eV, are respectively asso- ciated with the Mn('2+) intraion transitions in the 3d('5) configuration: ('6)A(,1)(('6)S) (--->) ('4)T(,1)(('4)G), ('6)A(,1)(('6)S) (--->) ('4)T(,2)(('4)G), and ('6)A(,1)(('6)S) (--->) ('4)A(,1), ('4)E(('4)G). A fourth absorption band (at 2.745 eV) although unidentified, is thought to be Mn related. Samples of the wurtzite crystal Cd(,1-x)Mn(,x)Se were studied at compositions x (TURN) 0.3, x (TURN) 0.42, and x (TURN) 0.45. In all samples, the intrinsic absorption edge exhibits the dichroism associated with the hexagonal structure. A strong Mn-related absorption edge is shown to exist in the two highest x samples at low temperatures, and is identified as the ('6)A(,1)(('6)S) (--->) ('4)T(,1)(('4)G) Mn('2+) intraion transition. The crystal field splitting (DELTA), obtained from the dichroism of the intrinsic edge, is found to be temperature dependent. A weak absorption band found below the Mn edge is known to give rise to the excitation spectrum of a known 1.35 eV emission band. Zn(,1-x)Mn(,x)Se is a zincblende crystal for x < 0.35 and wurtzite for 0.35 < x < 0.57. Samples with x (TURN) 0.23, x (TURN) 0.35, and x (TURN) 0.5 were studied. Three absorption bands with maxima at (TURN)2.42, (TURN)2.54, and (TURN)2.70 eV, are identified as the same three Mn related bands observed in Zn(,1-x)Mn(,x)Te. A higher absorption band at ((TURN)2.92 eV) is also seen. Polarization effects in the Mn-related absorption bands appear to be systematic. A region of broad absorption is seen below the Mn edge. The temperature dependent dichroism observed at high x in Cd(,1-x)Mn(,x)Se is also found in wurtzite phase Zn(,1-x)Mn(,x)Se. Both behaviors are explained in terms of an acceptor-bound magnetic polaron. In all samples with high x, an anomalous increase in the energy of the intrinsic absorption edge occurs below the LN(,2) temperature. This result is understood on the basis of a blue shift of the intrinsic edge due to the onset of a magnetic phase transition.
Degree
Ph.D.
Subject Area
Condensation
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