EXPERIMENTAL AND THEORETICAL STUDIES OF THE OPTICAL PROPERTIES OF II-VI SEMICONDUCTORS (VERDET CONSTANT, DIELECTRIC CONSTANT, TEMPERATURE DEPENDENCE)

ALLEN EDWARD TURNER, Purdue University

Abstract

There is a great deal of interest in II-VI materials for use in optical devices. Their combination of large bandgap and the ability to tailor bandgap through alloying make II-VI materials suitable for use over a wide range of wavelengths and allows superlattice and quantum wells to be fabricated. In addition, the inclusion of a magnetic ion, such as Mn, causes these materials to exhibit large magnetic effects which makes these materials suitable for use in isolators. Isolators are nonreciprocal devices used to stabilize sources by eliminating unwanted reflections from the load. The principal component of an isolator is a material that exhibits the nonreciprocal Faraday effect which is characterized by the Verdet constant. The Verdet constant and an associated figure of merit are measured for Cd(,0.55)Mn(,0.45)Te. Our measurements show bulk CdMnTe to exhibit a large Verdet constant with acceptable figures of merit over a broad range of wavelengths. However, there is little experimental data available for the other optical properties of these materials. A combined experimental and theoretical technique has been developed for the calculation of the dielectric constant of II-VI semiconductors. The technique determines the contribution of the (GAMMA) band region of the Brillouin zone from first principles while the contributions of the other regions are calculated from experimentally measured reflection spectra. The (GAMMA) band plays the major role in the changes in the dielectric constant due to changes in temperature, magnetic fields, quantization and possibly strain so this technique allows the calculation to be extended to account for these perturbations. A major finding of this work is the determination that the (GAMMA) band is not the major contributor to either the magnitude or slope of the total dielectric constant. This is in direct conflict with the results obtained by other researchers. A technique is developed for the calculation of the Verdet constant. The Verdet constant is calculated for Cd(,1-x)Mn(,X)Te for different values of X and for different temperatures. The results of these calculations are compared with experimentally determined Verdet constant values. An important aspect of the Verdet constant calculation is the proper determination of the slope of the dielectric constant due to the (GAMMA) band region of the Brillouin zone. The experimental Verdet constant data supports our calculation for the dielectric constant.

Degree

Ph.D.

Subject Area

Electrical engineering

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