We have determined the efficiency of photoionization of Ge¯-DX state in GaAs as a function of photon energy. The optical ionization energy derived from the fitting is about 1.0 eV. It proves a large difference between optical and thermal ionization energies and confirms that for Ge-impurity, the broken-bond model and large lattice relaxation are valid and not the breathing mode with small lattice relaxation, resulting from the calculations presented for Ge-impurity in T.M. Schmidt, A. Fazzio, M.J. Caldas, Mater. Sci. Forum 196/201, 273 (1995).
The diffusive maxima of phonon signals are studied for a number of solid solutions of rare earth atoms in yttrium aluminum garnets. The used exact formula for the diffusion constants allows for qualitative discussion of the obtained results. The established energy of phonons, forming the diffusive maximum of phonon signal of the temperature T_{H} arriving at the bolometer, ranges from 3.2k_{B}T_{H} to 4.2k_{B}T_{H}, which is in reasonable agreement with the existing estimations. The qualitative analysis allows us to estimate the contribution, made by the rare earth ions occupying the octahedral positions of the sixfold oxygen coordination, to the scattering of phonons due to lattice imperfections in yttrium aluminum garnets.
The phonon frequency line widths related to the phonon relaxation times is evaluated for impurity, anharmonic and interference scattering processes using double time temperature dependent Green's function method. The effects of force constant changes at impurity site and interference mode (new vibrational mode) on lattice thermal conductivity are the new features of the work. A few comments are made on the additivity of inverse relaxation times. The theory have been utilized to analyse the lattice thermal conductivity of ten synthetic aluminum garnets containing trivalent rare earth ions using Callaway's formula. The calculations show excellent agreements between theory and experiments.
The photoluminescence of homoepitaxial and heteroepitaxial GaN layers is reported. It is shown that the coupling between LO phonons and neutral acceptor bound excitons is much stronger than the coupling between LO phonons and neutral donor bound excitons. In undoped homoepitaxial layer, in spite of that the no-phonon emission due to donor bound excitons is one order of magnitude stronger than the acceptor bound excitons emission, the predominant structure in the LO phonon replica of the excitonic spectrum is related to optical transitions involving acceptor bound excitons. Temperature studies showed that at higher temperature the LO phonon replica is related to free excitons.
An anharmonic character for the Raman processes of the electron spin-lattice relaxation of paramagnetic defect centres in γ-irradiated potassium selenate and Rochelle salt single crystals was observed at low temperatures.
In the present work the scattering properties of a monolayer atomic lattice with grafted adatomic chains are investigated. In the case of two grafted lines, separated by a fixed distance, the localized states induced by the defect are determined. The transmission spectra are also obtained for various distances between the two chains and for additional chains regularly spaced. On the one hand, some Fabry-Perot oscillations are observed; their number is directly related to the number of adatomic lines. On the other hand, Fano resonances due to interaction between the localized states and the continuum are obtained. When the mass value of the adatom decreases, it is shown that the resonances move towards high frequencies in agreement with the harmonic oscillator frequency. Another novelty in this work consists of the observation of zeros of transmission in the spectra.
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