Photoluminescence and absorption study of the diluted magnetic semiconductors zinc(1-x)manganese(x)selenium, zinc(1-x)manganese(x)tellurium and zinc(1-x)manganese(x)sulfur
Abstract
A study of the optical properties of Zn$\sb{\rm 1-x}$Mn$\sb{\rm x}$Se was carried out using photoluminescence, photoluminescence exictation spectroscopy, time resolved spectroscopy, and optical absorption. Bulk crystals were investigated in the concentration range 0.0 $\leq$ x $\leq$ 0.5 (where x is the Mn mole fraction). Zincblende epitaxial layers (100) grown by molecular beam epitaxy (MBE) with x = 0.15, x = 0.23, x = 0.33 and x = 0.5, were also examined. Bulk crystals were annealed in molten zinc to investigate impurity emission and to permit access to the Mn$\sp{2+}$ emission band. Five visible emission bands are shown to be present in Zn$\sb{\rm 1-x}$Mn$\sb{\rm x}$Se. The $\sim$ 2.15 eV emission band is ascribed to the $\sp4$T$\sb1$($\sp4$G) $\to \sp6$A$\sb1$($\sp6$S) internal transition of the Mn$\sp{2+}$ ions. The two bands at $\sim$2.3 eV and $\sim$1.95 eV are related to the presence of Cu impurities, while the band at $\sim$2.03 eV is due to Zn vacancies. The fifth band at $\sim$1.7 eV is of unknown origin but may be related to Mn$\sp{2+}$ ions in a perturbed environment. Investigation of bulk crystals indicates that the 1.97 eV band in Zn$\sb{\rm 1-x}$Mn$\sb{\rm x}$Se originating in Cu impurities may be removed by annealing in molten Zn. The Cu emission band is discussed in terms of a model of thermally activated energy transfer from the excited Mn ions to Cu trapping centers, with thermal quenching of the process. Infrared absorption studies were carried out to identify the Cu accepter level. This level could only be observed in samples that were heavily doped with Cu. The $\sim$2.15 eV Mn$\sp{2+}$ emission band in Zn$\sb{\rm 1-x}$Mn$\sb{\rm x}$Se (0.05 $\leq$ x $\leq$ 0.50) was investigated over the temperature range from 4.2K to 293K in both MBE grown epilayers and zinc-annealed bulk crystals. A study of the polarization dependence of the optical absorption of the Mn$\sp{2+}$ ions in Zn$\sb{0\cdot85}$Mn$\sb{0\cdot15}$Se was carried out to extend the results first observed in Zn$\sb{\rm 1-x}$Mn$\sb{\rm x}$Se. The model shows that no polarization dependence should be present in any of the Mn$\sp{2+}$ absorption bands. (Abstract shortened with permission of author.)
Degree
Ph.D.
Advisors
Becker, Purdue University.
Subject Area
Condensation
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.