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Within the framework of the Huang–Rhys model, we study multiphonon replicas of excitonic spectroscopy in monolayer transition metal chalcogenides based on excitons coupled with three types of phonon modes. The phonon replicas for the longitudinal optical (LO) phonon modes and surface optical (SO) phonon modes induced by the polar substrate Al 2O 3 are given and a linewidth of the phonon replica arising from the exciton-longitudinal acoustic phonon interaction is proposed. We find that the intensity distribution and temperature dependence of the phonon replicas are in good agreement with the experimental measurement. Furthermore, we propose combinational phonon replicas of p L O ℏ ω L O + p S O ℏ ω S O between two optical phonon modes, which effectively fill the gaps between the replicas of the single phonon modes. These theoretical results provide some insight into the detailed analysis of excitonic spectroscopy.

Rutile structured SnO2 nanobelts have been synthesized from the mixture of Sn powders and SiO2 nanoparticle powders. Each nanobelt has a uniform width of about several hundred nanometers and a thickness of about tens of nanometers along its entire length. Micro-Raman spectrum measurement on the SnO2 nanobelts shows that the first-order Raman A1g mode (632.9 cm−1) is very strong, and two weak Raman bands 498 and 694 cm−1 seem to correspond to infrared (IR)-active longitudinal optical (LO) and transverse optical (TO) of A2u modes. In addition, the IR spectrum of the SnO2 nanobelts shows the A2u (LO) (701.9 cm−1) and Eu (1) (TO) (634.5 cm−1) modes and one surface mode (565.2 cm−1). The IR-active bands in the Raman spectrum and the surface mode in IR spectrum, which may be due to the nanoscale morphology of the nanobelts.

Interfacial oxide structures were studied by Infrared reflection absorption spectroscopic analysis. The longitudinal optical mode of the interfacial oxide films arose with lower frequencies and wider widths. We assumed and later verified that these changes resulted from the contribution of interfacial roughness. We therefore examined the contribution of interfacial roughness to the infrared spectra using the effective medium approximation model and via infrared spectra simulation. The experimental results explained by a model of that interface had an atomically roughness of within 1 nm and chemical structure changes effectively little fluctuation.

Raman scattering measurements on low temperature GaAs layers are presented. Phonons in both GaAs and As are studied. The transition from diluted As in the GaAs matrix to the small As clusters formed after annealing is analyzed. This is performed by observing the reduction of the GaAs bound charge, i.e., the longitudinal optical GaAs frequency downshift, to the appearance of the crystalline As vibrational mode. From the phonon shifts of crystalline As, the diameter and the strain are derived, accordingly to transmission electron microscopy measurements.

The decay of the zone-center longitudinal optical (LO) phonon in GaN into a transverse optical (TO) phonon and a longitudinal acoustic (LA) phonon is theoretically investigated. Its decay into two LA phonons is forbidden. A theoretical model is presented to study the effect of nonequilibrium LO and TO phonons on the electron energy relaxation rate. The electron energy relaxation time is calculated, and its value is shown to strongly depend on the finite lifetimes of both LO and TO phonons. The individual contributions of A1 mode and E1 mode optical phonons in the overall electron energy relaxation processes are also discussed.

Bulk ZnS crystals have been examined by Raman spectroscopy at room temperature under uniaxial stress. Both transverse optical and longitudinal optical frequencies exhibit shifts which are linear in the stress. From the observed slopes we obtain the complete set of phonon deformation potentials which, in turn, are used to predict the LO phonon frequency shifts in strained ZnTe/ZnS and ZnSe/ZnS superlattices as a function of the layer thickness. The results are in agreement with previously reported values obtained from Raman measurements in such superlattices.

Resonant Raman scattering by longitudinal optical phonons has been used to study the effect of annealing in a hot Hg bath on 113In+ and 11B+ implanted Cd0.23Hg0.77Te. Up to the highest doses of 1×1013 cm−2 for In and 1×1014 cm−2 for B, respectively, Raman spectroscopy indicates a full recovery of the crystalline perfection for annealing temperatures around 320 °C and annealing times ≥10 min. This recovery is accompanied by an electrical activation of the implants. Control experiments have been carried out to prove that the electrical activity is not due to residual lattice damage and that the immersion in the Hg bath by itself has no effect on the Raman spectrum.

We have observed by off‐resonance Raman scattering confined longitudinal optical phonon modes in the ZnSe layer of a ZnSe‐ZnTe strained‐layer superlattice which has a lattice mismatch as large as 7.3% at room temperature. We have calculated the red shifts of phonon frequencies due to confinement and the shifts induced by the elastic strains, which are much larger than the red shifts due to confinement. The red shifts induced by tensile strain in the ZnSe layer and the blue shifts induced by compressive strain in the ZnTe layer caused some confined LO modes in two individual layers overlap. Therefore, the folded LO mode has been observed in the ZnSe‐ZnTe strained‐layer superlattice.

The linear‐chain approximation is used to calculate the spectrum of confined longitudinal‐optical (LO) phonon frequencies in short‐period strained‐layer superlattices. The frequencies for confined LO‐phonon modes are reported explicitly for the case of GaAs/GaP short‐period strained‐layer superlattices grown in the 〈001〉 direction. These results are compared with the few existing experimental measurements for such superlattices.

Raman scattering studies were performed on ZnSe–ZnS strained‐layer superlattices with different strains. In the optical phonon regime, the Raman spectra of the ZnSe–ZnS superlattices with a superlattice axis along [001] show optical phonons confined in the ZnSe well and ZnS barrier layers, and display a two‐mode behavior corresponding to ZnSe‐like and ZnS‐like modes. We report the experimental results, by means of Raman scattering of confined longitudinal optical phonons in ZnSe–ZnS strained‐layer superlattices. The Raman frequency shift dependence on the layer thickness, superlattice period, and interface strain is presented and discussed.

The important role of confined longitudinal optical (LO) and surface optical (SO) phonons is investigated for different types of individual scattering processes in AlGaAs/GaAs quantum wires. Electron wave function tailing due to finite barrier height has been properly taken into account. We demonstrate that for highly confined wires structures Ly=Lz=40 A, forward and backward scattering are dominated by SO phonons. For 80 A×80 A structures, forward scattering is still predominately by SO phonons while backward scattering is dominated by confined LO phonons. Finally, for 150 A×150 A, confined phonons control both forward and backward scattering. However, we demonstrate that confined LO phonons play a dominant role in intersubband transitions even in highly confined structures, and that it has the most significant effect on the backward scattering in quantum wires of Ly=Lz≳80 A.

Hyperferroelectricity is a new phenomenon discovered recently [Garrity et al., Phys. Rev. Lett. 112, 127601 (2014)]. Based on a fourth-order Ginzburg-Landau energy expansion, we formulate a physical constraint that hyferroelectrics must satisfy. The constraint leads to a nonzero polarization under the open-circuit boundary condition as well as a stable electric state as the minimum of the free energy. The theory further reveals a guide principle on the search for new hyferroelectrics, i.e., they need to have a deep potential well and a small zero-field polarization. In addition, we show that an unstable longitudinal optical phonon is a natural consequence of the constraint. Prototypical ferroelectric BaTiO3, PbTiO3, and KNbO3 do not meet the physical constraint, and are not hyperferroelectrics.

We demonstrate optical control of the LO phonon-plasmon coupled (LOPC) modes in GaAs by using a femtosecond pump-pulse pair. The relaxation time of the plasmon-like LOPC mode significantly depends on the separation time (\Delta t) of the pump-pulse pair. Especially it is maximized when \Delta t becomes simultaneously comparable to the half period of the longitudinal optical (LO) phonon oscillation and resonant to the 3/4 period of the plasmon-like LOPC oscillation. We attribute these observations to the modification of carrier-LO phonon scattering and ballistic motion of the plasmon-like LOPC mode., Comment: 5 pages, 4 figures, submitted to Journal of Applied Physics

The multiphonon-assisted photoluminescence (PL) of the single wall carbon nanotubes (SWNTs) have been studied by solving the Schrodinger equation, showing a set of phonon sidebands, both the Stokes and anti-Stokes lines, which are induced by the longitudinal optical phonon and radial breathing mode phonon. All the calculated results are in a good agreement with the recent experimental PL spectra of the SWNTs [F. Plentz, H. B. Ribeiro, A. Jorio, M. S. Strano, and M. A. Pimenta, Phys. Rev. Lett. 95, 247401 (2005)] and J. Lefebvre and P. Finnie, Phys. Rev. Lett. 98, 167406 (2007)]. In addition, it is very interesting to find in the calculated PL several additional phonon sidebands with rather weak intensities, which are caused by the exciton’s coupling with two kinds of phonons, and expected to be observed in future experiments.

Temperature-dependent photoluminescence of MgZnO alloy film has been studied, and it is found that the emission intensity increases significantly at a certain temperature range and then decreases when increasing temperature further. The anomalous increase is resulted from the localized excitons in MgZnO alloy, as revealed by the enhanced second-order longitudinal optical phonon in the Raman spectrum of the MgZnO film. A schematic model was suggested to depict the carrier transportation process in the MgZnO film considering the existence of localized exciton states. The results reported in this paper indicate that localized excitons in MgZnO alloy can result in greatly enhanced emission efficiency, which is eagerly wanted for the application of ZnO-based materials in high-efficiency light-emitting devices.

The coupling between exciton and longitudinal optical (LO) phonon was investigated in the use of temperature-dependent photoluminescence from MgxZn1−xO powders prepared by a sol-gel method in the range of 0≤x≤0.05. The exciton binding energy increases to 73 meV for 5 at. % Mg incorporated powders. The strength of exciton–LO phonon coupling was deduced from the energy shift of exciton emission with temperature variation. The increase of the exciton binding energy results from a decrease of the exciton Bohr radius that is responsible for reducing the coupling strength of exciton–LO phonon as increasing Mg content.

Raman spectra from InP were measured at various power densities of the exciting laser. Concentration of the optically excited excess carriers Δn calculated from the frequency of the coupled longitudinal optical phonon‐plasmon mode was about 0.5–1.7×1017 cm−3 at the laser power density of 5×102 W/cm2 for InP with equilibrium carrier concentration 0.9–5×1017 cm−3. Surface recombination velocity estimated from Δn assuming that the bulk lifetime was larger than 10−7 s was 1–8×103 cm/s. Such dependence of Raman spectra on laser power density could not be observed for GaAs.

The mobility of n‐InSb at cryogenic lattice temperatures is shown to change during approximately 10 nsec after application of a voltage pulse. It increases with time below a certain electric field strength and decreases above this value. This behavior can be understood as resulting from a deviation of the longitudinal optical phonon distribution from its thermal equilibrium; the stationary state being obtained approximately 10 nsec after application of the voltage pulse.

The longitudinal optical phonon‐plasmon interaction theory of Varga is shown to be applicable to Gadoped CdS through the region of the first reflectivity minumum (2.5 to about 30 μ). The theoretical reflectivity vs wavelength for several concentrations of Ga‐doped CdS are compared with experiment. The agreement between theory and experiment is particularly good for high dopant concentrations. A plot of the wavelength at minimum reflectivity vs impurity concentrations shows that the Varga theory does well in explaining the data. When phonon damping is introduced into the Varga dielectric function, the reflectivity over the whole region of resonance is more realistic. Finite plasmon lifetime is not considered since no data are available for CdS.

A classical theory of electron energy loss is used to calculate the breakdown field of quartz as 1.0×107 V/cm. The method makes use of the dielectric dispersion curves to determine the electron energy loss via interaction with the longitudinal optical (LO) phonon modes. The 0.153‐eV LO mode is the dominant mode in determining the breakdown. The results for quartz should also be applicable to amorphous SiO2 since the optical phonon modes are strongly localized and the nearest‐neighbor configuration is maintained for both silica and quartz. The 1.0×107 V/cm breakdown calculation is in excellent agreement with the highest breakdown fields measured for amorphous SiO2 films.

The interaction between longitudinal optical phonons in an insulator and electrons tunneling through the insulator is investigated on the basis of a simple one‐dimensional model. This interaction is found to alter the mechanism of metal‐insulator tunneling drastically, the tunneling current being constant at low temperatures and highly temperature‐dependent at room temperature. The low‐field (≲106V/cm) current‐voltage relationship has an algebraic form similar to that for thermionic emission but differs from it in magnitude and temperature dependence. It is concluded that the high‐ and low‐temperature regions of charge transfer from metal to insulator are continuous, representing the evolution of the electron‐phonon interaction with temperature.