B.P. Clayman

Long wavelength lattice vibrations in GaS and GaSe

Abstract The first order Raman spectra and far infrared absorption spectra of GaS and GaSe have been investigated and interpreted. A correspondence is drawn between the observed vibrational modes of the two crystals and a Raman active polar longitudinal mode has been identified in GaSe. The results are consistent with the existence of GaS in a β-polytype (D6h) and GaSe in an ϵ-polytype (D3h).

The superconducting energy gap of NbSe2

Abstract The energy gap of NbSe2, a superconducting layer structure, has been measured to be 2.15 meV at 1°K by observing its far-infrarad tranmission spectrum. The temperature dependence of the gap is found to be consistent with B.C.S. predictions.

Lattice modes of Zn3P2

Abstract Optical spectra of Zn 3 P 2 in the far infrared region (40–700cm -1 ) have been measured at room temperature and at 8K. By means of Kramers-Kronig analysis, the optical constants and the energies of the zone-center TO and LO phonons have been determined. Two-phonon effects were observed and correlated with the energies of the TO and LO phonons.

Far-infrared reflectivity of the mixed-valence compounds TmTe and TmSe☆

Abstract Far-infrared reflectivity measurements have been made on the mixed valence compounds TmTe and TmSe between 1.3 and 300 K. For TmTe at 1.3 K a single Reststrahlen band is observed at frequencies expected for divalent Tm in TmTe. At 4.2 K new weak structure appears which may be due to trivalent Tm. TmSe shows a surprisingly low reflectivity, but no phonon structure. The plasma edge is at ∼ 10cm -1 indicating a strongly frequency-dependent conductivity.

Infrared reflectance studies on silver intercalated TiS2

Abstract Infrared reflectance studies were carried out on Stage 1 and Stage 2 single crystals of silver-intercalated TiS 2 . The spectra clearly showed the Drude edge and were analyzed using the single carrier Drude model. The Drude parameter values, plasma frequency (ω p ), damping constant (Γ), high frequency dielectric constant (e ∞ ) and carrier concentration were calculated.

A classical oscillators model for infrared reflectance spectra of Zn3P2

Abstract Reflectance spectra of Zn3P2 monocrystals measured in the restrahlen region at 10 and 300 K were analyzed by means of classical oscillators fit. The 18 transverse phonon modes were described by the oscillator parameters: mode frequency, oscillator strength and the damping constant. The influence of the initial values of the fitting parameters on the results of the optimization procedure was discussed.

A pair-mode in the far infrared absorption spectrum of KCl:NaCl☆

Abstract A new resonance at 36 cm-1 has been observed in the far infrared absorption spectrum of KI:Cl-. The quadratic concentration dependence of the line strength indicates that the absorption is due to pairs of chlorine ions. A simple molecular model calculation indicates that a large softening of the short range force constants occurs around the defect, in agreement with previous single ion calcualtions.

Lattice modes and charge density waves in 1T-TaS2

Abstract The far-infrared reflectivity of 1T-TaS 2 was measured at 100, 295 and 390 K. At the two highest temperatures, the spectra were featureless. Overall reflectivity dropped abruptly in cooling through 350 K and through 190 K. These transitions are correlated to CDW formation. At 100 K five strong bands and at least two weak bands were observed. These are attributed to lattice vibration which can be excited optically as a result of the breakdown of selection rules due to the formation of a large superlattice by the onset of CDW.

PHOTOLUMINESCENCE AND INFRARED ABSORPTION STUDIES OF DOUBLE ACCEPTORS IN GERMANIUM

Abstract Recent studies of double acceptors using near-, mid-, and far-infrared spectroscopy are reviewed, and new results are presented in each of these areas. Bound excitons and bound multiexciton complexes associated with these centers are investigated using photoluminescence and near-infrared absorption spectroscopy, and also measurements of the far-infrared absorption due to transitions between bound exciton states. Many bound exciton excited states are observed, and are well explained by a pseudo-donor model. The earlier predictions that the double acceptor ground states were split by hole-hole coupling, which were based upon near-infrared results and the temperature dependence of the mid-infrared neutral acceptor absorption, are verified by detailed uniaxial stress measurements of Ge:Be and Ge:Zn.

Photoluminescence and infrared absorption studies of Ge doped with Mg

Abstract The photoluminescence spectrum of Ge doped with the double acceptor Mg reveals lines due to both bound excitons and bound multiexciton complexes, which are in some ways similar to those previously reported for Ge:Be and Ge:Zn. As in Ge:Zn, the Ge:Mg bound exciton line was found to be a doublet, showing that the Mg double acceptor in Ge also has a split ground state. Further evidence for this ground state splitting is found from the temperature dependence of the infrared absorption spectrum of the Mg double acceptor.