Fourier transform infrared and Raman spectroscopy of elemental and compound semiconductors: Electronic and vibrational excitations

Hyunjung Kim, Purdue University

Abstract

The Lyman spectrum of substitutional boron acceptors in diamonds with natural composition and that in a $\sp{13}$C diamond exhibit remarkably similar features, but shifted to higher energies in the latter by 0.4-1.5 meV. Additional lines appear when the spectra are recorded as a function of temperature, indicating the thermal population of a level $\Delta\sp\prime\sim2$ meV above the ground state; this can be interpreted as the spin-orbit splitting of the 1s acceptor ground state into $1s(p\sb{3/2})$ and $1s(p\sb{1/2}),$ the latter located $\Delta\sp\prime$ above the former. The Raman allowed $1s(p\sb{3/2})\to1s(p\sb{1/2})$ electronic transition is directly observed at 2.07(1) and 2.01(1) meV in the Raman spectrum of natural and $\sp{13}$C diamond, respectively. Polarization features of the $\Delta\sp\prime$ Raman line reveal that it is predominantly $\Gamma\sb5$ in character, as predicted by a theoretical calculation formulated in terms of the known values of Luttinger parameters. The theoretical expression for the Raman cross section for $\Delta\sp\prime$ enables the acceptor concentration to be deduced from an intercomparison of the intensity of the $\Delta\sp\prime$ line and that of the zone-center optical phonon. The presence of boron acceptors produces a quasicontinuous absorption spectrum in the range of the optical phonon branch, flanked by a sharp feature at the zone-center optical phonon frequency; their appearance can be attributed to the partial breakdown of the translational symmetry and the activation of otherwise inactive vibrations. The theory for the piezo- and magnetospectroscopy of the $\Delta\sp\prime$ line is outlined and preliminary experimental results are presented. The power of the Fourier transform infrared spectroscopy is applied to study of: (1) Lyman spectra of electrons bound to group V donors in Ge, yielding the valley-orbit splitting of the ground states $(4\Delta\sb{c}).$ (2) The optical phonons of polar semiconductors grown by molecular beam epitaxy as epilayers (MnSe epilayers with NaCl structure grown on GaAs substrates and GaSb or AlSb epilayers grown on GaAs, and ZnTe on GaSb). (3) Localized vibrational modes of light impurities in III-V compound semiconductors (Zn or As in GaSb).

Degree

Ph.D.

Advisors

Ramdas, Purdue University.

Subject Area

Condensation|Materials science

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