Far-infrared magneto-optical spectroscopy of semiconductors in bulk and epitaxial layer form
Abstract
Far-infrared (FIR) magneto-transmission measurements were performed on the following semiconductor system: the multinary alloy (Hg$\sb{\rm 1-x}$Mn$\sb{\rm x}$Te)$\sb{\rm 1-y}$(FeSe)$\sb{\rm y}$; MBE-grown epitaxial layers of CdTe and CdTe:In; and MBE-grown epitaxial layers of HgTe and Hg$\sb{\rm 1-x}$Mn$\sb{\rm x}$Te, on Cd$\sb{\rm 1-x}$Zn$\sb{\rm x}$Te substrates. The study of the multinary (Hg$\sb{\rm 1-x}$Mn$\sb{\rm x}$Te)$\sb{\rm 1-y}$(FeSe)$\sb{\rm y}$ alloy focused on the understanding of the nature of magnetic interaction between the Mn$\sp{++}$ and the Fe$\sp{++}$ ions. A theoretical approach to the magnetic properties and the exchange interaction in Hg$\sb{\rm 1-x}$Fe$\sb{\rm x}$Te was established. Having tested our theoretical approach on data available in the literature for Hg$\sb{\rm 1-x}$Fe$\sb{\rm x}$Te, we were then able to apply the same approach to (Hg$\sb{\rm 1-x}$Mn$\sb{\rm x}$Te)$\sb{\rm 1-y}$(FeSe)$\sb{\rm y}$ by extending the exchange formulation to a model (based on the Pidgeon-Brown band model) in which two kinds of magnetic ions (i.e., Mn$\sp{++}$ and Fe$\sp{++}$) exist simultaneously. Our analysis of the experimental data indicates that the interaction between the two types of ions is antiferromagnetic, reducing the total magnetization below the value which would result from simply adding the magnetizations of the Mn$\sp{++}$- and Fe$\sp{++}$-sub-systems. We observe a splitting of the 1s-to-2p transition in the CdTe:In epitaxial layer grown on a CdTe substrate, which can not be explained by any known mechanism associated with bulk samples. Cyclotron resonance measurements carried out at higher temperature indicate that the mobility (obtained from the cyclotron resonance linewidth) in the CdTe:In epitaxial layer is about two orders of magnitude higher than that obtained from transport measurements. All the observed effects show no 2-dimensional behavior and no anisotropy with respect to the growth direction. FIR magneto-transmission spectra of epitaxial layers of HgTe and of Hg$\sb{\rm 1-x}$Mn$\sb{\rm x}$Te with different Mn concentrations show that the epitaxially grown crystals are of much better quality compared to similar bulk samples grown by the traditional Bridgeman technique. It is suspected that the large amount of Hg vacancies characteristic of the bulk samples are greatly reduced in the MBE-grown samples. Otherwise, the magneto-optical properties of such layers are very similar to those of the bulk samples, in spite of the existence of the interfaces, and of the lattice mismatch.
Degree
Ph.D.
Advisors
Furdyna, Purdue University.
Subject Area
Condensation
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