Raman, Brillouin and photoluminescence spectroscopy of elemental and compound semiconductors
Abstract
The effects of the zero-point motion and the anharmonicity of the lattice vibrations of diamond are explored theoretically employing a valence force model explicitly incorporating the isotopic composition $\sp{12}$C$\sb{1-x}\sp{13}$C$\sb{x}\ (0 \leq x \leq 1)$. The predictions are tested in a study of the elastic moduli ($c\sb{ij}$) deduced from Brillouin spectra and the zone center optical mode frequency ($\omega\sb0$) from Raman spectra. It is predicted that the bulk modulus of $\sp{13}$C diamond exceeds that for $\sp{12}$C diamond by one part in a thousand, just below the experimental sensitivity accessible with Brillouin measurements; $\omega\sb0$ is found to exceed the value expected from the $M\sp{-1/2}$ dependence, $M = (1 - x)M\sb{12} + xM\sb{13}$, by $\sim$0.3 cm$\sp{-1}$, consistent with observation. The elastic moduli for natural diamond determined in the present study, viz., $c\sb{11}$ = 10.804(5), $c\sb{12}$ = 1.270(10) and $c\sb{44}$ = 5.766(5) in units of 10$\sp{12}$(dyn/cm$\sp2$) are the most accurate yet obtained. From a new study of the two-phonon Raman and infrared spectra of diamond, along with the polarization characteristics of the former, and exploiting space group selection rules, the frequencies of all the symmetry-related critical points of the Brillouin Zone are deduced with significant precision. Indirect transitions, free and impurity-bound excitons in gallium phosphide are revisited with photoluminescence spectroscopy. From the observed signatures of sulfur- and nitrogen-bound excitons and their phonon-sidebands, zone-center and zone-boundary phonon frequencies are deduced. They agree with the values for the first order Raman lines and the zone boundary phonons from the signatures of the indirect transitions mediated by phonons at the X-point, which appear in the spectrum of piezo-modulated transmission. The multi-mode behavior of the zone center optical phonons in bulk crystals of the tetrahedrally coordinated Cd$\sb{1-x-y}$Zn$\sb{x}$Mg$\sb{y}$Te ($0 \leq x,\ y \leq 1$) semiconductor alloys is investigated using Raman spectroscopy. Two mode behavior in Zn$\sb{1-x}$Mg$\sb{x}$Te and three mode behavior in Cd$\sb{1-x-y}$Zn$\sb{x}$Mg$\sb{y}$Te are observed in Raman scattering. The dependence of the "MgTe-like", "ZnTe-like" and "CdTe-like" TO and LO frequencies on composition (x,y) is delineated and interpreted with the modified random isodisplacement model.
Degree
Ph.D.
Advisors
Ramdas, Purdue University.
Subject Area
Condensation|Materials science
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