Spectroscopic signatures of novel oxygen-defect complexes in stoichiometrically controlled CdSe.

Growth of single crystals of CdSe with oxygen, introduced by stoichiometric control to suppress the formation of native Se and Cd vacancies, generates oxygen centers replacing Cd (O Cd) rather than Se (O Se) as expected. This antisite substitution is unambiguously singled out by the host isotope fine structure of the nearest neighbor (NN) Se atoms in the localized vibrational modes (LVMs) of O Cd. When the stoichiometry control favors the formation of Cd vacancies, three infrared signatures gamma1, gamma2 and gamma3 appear ascribable to the LVMs of O Se in association with a Cd vacancy in the NN position as (O Se-V Cd) centers.

Stoichiometry driven impurity configurations in compound semiconductors.

Precise stoichiometry and departures therefrom in the composition of the tetrahedrally coordinated compound semiconductors allow impurity incorporation in more than one configuration. Ultrahigh resolution infrared spectroscopy of CdTe:O at low temperatures reveals a unique sharp doublet associated with the local vibrational modes of OTe in a (OTe-VCd) complex with nearest neighbor Cd vacancy VCd and a single sharp line attributed to the local vibrational mode of OTe in a perfect CdTe. The uniaxial (C3v) symmetry of (OTe-VCd) transforms to Td symmetry at T* approximately 300 K, acquired due to an increasing rate of dynamic switching of the "OTe-VCd" dangling bond in which the vacancy and its three next nearest neighbor Cd cations exchange positions as temperature (T) approaches T*; for T>or=T*, the doublet thus transforms into a single, triply degenerate line.

Fe vibrational spectroscopy of myoglobin and cytochrome f.

The Fe vibrational density of states (VDOS) has been determined for the heme proteins deoxymyoglobin, metmyoglobin, and cytochrome f in the oxidized and reduced states, using nuclear resonance vibrational spectroscopy (NRVS). For cytochrome f in particular, the NRVS spectrum is compared with multiwavelength resonance Raman spectra to identify those Raman modes with significant Fe displacement. Modes not seen by Raman due to optical selection rules appear in the NRVS spectrum.

Lifetimes of hydrogen and deuterium related vibrational modes in silicon.

Lifetimes of hydrogen and deuterium related stretch modes in Si are measured by high-resolution infrared absorption spectroscopy and transient bleaching spectroscopy. The lifetimes are found to be extremely dependent on the defect structure, ranging from 2 to 295 ps. Against conventional wisdom, we find that lifetimes of Si-D modes typically are longer than for the corresponding Si-H modes.

Interaction of localized electronic states with the conduction band: band anticrossing in II-VI semiconductor ternaries.

We report a strongly nonlinear pressure dependence of the band gaps and large downward shifts of the conduction band edges as functions of composition in ZnS xTe (1-x) and ZnSe (y)Te (1-y) alloys. The dependencies are explained by an interaction between localized A1 symmetry states of S or Se atoms and the extended states of the ZnTe matrix. These results, combined with previous studies of III-N-V materials define a new, broad class of semiconductor alloys in which the introduction of highly electronegative atoms leads to dramatic modifications of the conduction band structure.