Participation Of Optical Phonons Research Articles

The role of nano-dimensional structural defects in the optical absorption of Bi12SiO20 crystals

Optical absorption of Bi12SiO20 crystals containing nonstoichiometry defects in the cation sublattices was studied in the temperature range 80 ÷ 600 K. It is shown that, at absorption coefficients the Urbach rule is fulfilled; while at indirect transitions with the participation of optical phonons take place. The value αt depends on temperature. The parameters of the Urbach rule change regularly when the Bi:Si stoichiometry is violated. The features of the isoabsorption dependences and the parameter σ characterizing the temperature change of the edge absorption are revealed.

Resonance Raman scattering and excitonic spectra in TlInS2 crystals

The excitons ground and excited states for E∥a and E∥b polarizations in absorption and reflection spectra of TlInS2 crystals were detected. The fundamental parameters of excitons and bands were determined at k=0. The resonance Raman spectra were investigated in the region of excitons transitions. The resonance Raman scattering spectra with participation of optical phonons that are active at the center of Brillouin zone were identified. The Raman scattering in Y(YX)Z and Y(ZX)Z geometries at 10K with excitation by He–Ne laser was researched. Energies of phonons with Ag and Bg symmetries were determined. It was shown that the number of modes at 10K was two times lower than expected according to theoretical calculations.

IR Absorption by Free Charge Carriers with the Participation of Optical Phonons in Structures with Quantum Wells

The absorption of light by free charge carriers with the participation of surface and bulk optical phonons is considered in terms of the Boltzmann statistics and Pekar-Frohlich Hamiltonian for the electron-photon interaction in a polar semiconductor layer within the framework of the model of a rectangular quantum well. It is found that the contributions of the surface and bulk modes to the probability of light absorption depend on the quantum-well width. It is demonstrated that the line of the photon-phonon resonance has a complex structure due to the difference between the frequencies of the bulk and surface optical vibrations. The influence of the adjacent media on the coefficient of light absorption is investigated.

Coherent control of optical-phonon-assisted resonance secondary emission in semiconductor quantum dots

A new optical effect, the coherent control of spontaneous secondary emission with the participation of optical phonons in systems with discrete spectra of electronic transitions, is studied theoretically. Analytical formulas are obtained that describe the time-integrated signals of secondary emission excited resonantly by a pair of phase-locked pulses in the homogeneously and inhomogeneously broadened systems of semiconductor quantum dots. It is shown that coherent control is a promising method for measuring the total dephasing rates of a resonance optical transition. A physically justified criterion for discriminating between scattering and luminescence in the secondary emission is found. The role of spectral filtering of the signal in the measurements of phase and energy relaxation parameters is elucidated.

Direct measurements of energy relaxation times on an AlGaAs/GaAs heterointerface in the range 4.2–50 K

The temperature dependence of the energy relaxation time τe (T) of a two-dimensional electron gas at an AlGaAs/GaAs heterointerface is measured under quasiequilibrium conditions in the region of the transition from scattering by acoustic phonons to scattering with the participation of optical phonons. The temperature interval of constant τe, where scattering by the deformation potential predominates, is determined. In the preceding, low-temperature region, where piezoacoustic and deformation-potential-induced scattering processes coexist, τ e decreases slowly with increasing temperature. Optical phonons start to participate in the scattering processes at T∼25 K (the characteristic phonon lifetime was equal to τLOτ4.5 ps). The energy losses calculated from the τe data in a model with an effective nonequilibrium electron temperature agree with the published data obtained under strong heating conditions.

Impurity recombination of hot current carriers with the participation of optical phonons

In the framework of a modified cascade capture theory, this work examines the recombination of hot current carriers at impurity attractive centers in semiconductors with, in the first stage, optical phonon capture assisting in conditions of the carrier distribution for scattering by zero-point lattice vibrations. Calculation of the effect on carrier recombination of the excited states of the impurity centers with binding energy is less than that given in the Lax model and leads to a more distinct negative differential resistance. The quantitative results obtained are evaluated and an estimate is made of the magnitudes of the processes hindering observation of recombination with the assistance of optical phonons.

Electron-phonon interaction in LiNbO3:Fe and sillenite crystals

Circular photogalvanic effect (CPGE) is observed in sillenite crystals, whereas linear photogalvanic effect (LPGE) is observed in LiNbO/sub 3/. The mechanisms of CPGE and LPGE are linked to the asymmetry of the electron-phonon interaction (EPI) and the inclusion of indirect transitions, which can also occur with the participation of optical phonons. The authors cite Raman scattering (RS) of light as one of the most promising tools for studying the electron-phonon interaction based on the polarized spectra of optical phonons. The experimental results obtained for the LiNbO/sub 3/: Fe crystals is examined, as well as for the Bi/sub 12/SiO/sub 20/ sillenite crystals.

On the electric field dependence of the conductivity of holes in Si at low temperatures. II. The influence of the variation of steady‐state hole density with electric field on the conductivity

AbstractMeasurements of the electric field dependence of the hole conductivity of Si with various doping levels and orientations are performed at 20.3 and 27.1 K. A description of the essential characteristics of the experimental results is achieved within the frame of a theoretical model. In this model, the field dependence of the hole mobility (taking into account non‐parabolicity of the valence band and non‐equipartition of acoustic phonon energy in the distribution function as well as in the momentum relaxation time) and the field dependence of the hole concentration (based on Lax′ cascade theory) are combined. Comparison of experimental and numerical results gives the relation between the participation of optical phonons in the hole capture process on shallow acceptors and the transition from super‐ to sublinear current‐voltage characteristics in high‐purity p‐Si at low temperatures and at electric field strengths below the breakdown range.