Complex energies of the coherent longitudinal optical phonon–plasmon coupled mode according to dynamic mode decomposition analysis

In a dissipative quantum system, we report the dynamic mode decomposition (DMD) analysis of damped oscillation signals. We used a reflection-type pump-probe method to observe time-domain signals, including the coupled modes of long-lived longitudinal optical phonons and quickly damped plasmons (LOPC) at various pump powers. The Fourier transformed spectra of the observed damped oscillation signals show broad and asymmetric modes, making it difficult to evaluate their frequencies and damping rates. We then used DMD to analyze the damped oscillation signals by precisely determining their frequencies and damping rates. We successfully identified the LOPC modes. The obtained frequencies and damping rates were shown to depend on the pump power, which implies photoexcited carrier density. We compared the pump-power dependence of the frequencies and damping rates of the LOPC modes with the carrier density dependence of the complex eigen-energies of the coupled modes by using the non-Hermitian phenomenological effective Hamiltonian. Good agreement was obtained between the observed and calculated dependences, demonstrating that DMD is an effective alternative to Fourier analysis which often fails to estimate effective damping rates.

Fröhlich interaction dominated by a single phonon mode in CsPbBr3

The excellent optoelectronic performance of lead halide perovskites has generated great interest in their fundamental properties. The polar nature of the perovskite lattice means that electron-lattice coupling is governed by the Fröhlich interaction. Still, considerable ambiguity exists regarding the phonon modes that participate in this crucial mechanism. Here, we use multiphonon Raman scattering and THz time-domain spectroscopy to investigate Fröhlich coupling in CsPbBr3. We identify a longitudinal optical phonon mode that dominates the interaction, and surmise that this mode effectively defines exciton-phonon scattering in CsPbBr3, and possibly similar materials. It is additionally revealed that the observed strength of the Fröhlich interaction is significantly higher than the expected intrinsic value for CsPbBr3, and is likely enhanced by carrier localization in the colloidal perovskite nanocrystals. Our experiments also unearthed a dipole-related dielectric relaxation mechanism which may impact transport properties.

Optical Signature of Bipolaron in Monolayer Transition Metal Dichalcogenides: All Coupling Approach

We studied the optical signature of bipolaron and its effects on the bandgap modulation in the single-layer Transition Metal Dichalcogenides (TMDs) under magnetic field. Using the Huybrecht method, we derived the ground state energies in the modified zero Landau levels for all Fröhlich coupling constants. We take into account both intrinsic longitudinal optical phonon modes and surface optical phonon modes induced by the polar substrate. We observed that the higher the coupling strength, the stronger is the magnetic field effect. The highest amplitude of the bandgap modulation is obtained for the MoS2 monolayer and the lowest with the WSe2 monolayer. We also found that the bipolaron is stable in TMDs. It is seen that the optical absorption presents the threshold values and respectively increases for WSe2, MoSe2, WS2 and MoS2.

Effect of Cd Substitution on Structural and Optical Properties of Zn1-xCdxSe Thin Films

In this research, Zn1-xCdxSe alloys (x from 0 to 1) were synthesized by solid-state microwave (SSM) method of producing thermally evaporated thin films. The cubic structure and the elemental ratios of the films were studied using X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy. The optical characterizations of the as-deposited film in terms of the energy band gap (Eg), photoluminescence (PL), and Raman shift spectra were conducted at the room temperature. The Eg values for the thin films from ZnSe to CdSe were 3.4 to 1.7 eV, respectively. The PL orange emission for ZnSe thin film at 565 nm, whereas 590 nm in the yellow region for CdSe thin film. From Raman shift spectra, the two longitudinal-optical phonon modes (1LO and 2LO) at 240, and 490 cm-1 are assigned for the ZnSe and CdSe thin films.

Computerized Fdtd Method for Longitudinal Optical Phonon Energy on Semiconductor Hybrid Structure for High Power Devices Fabrication

The research problem in this study is the longitudinal optical phonon energy on metal/semiconductor interface for high performance semiconductor device. The research solution is to make the software model with finite difference time domain (FDTD) solution for transmission and reflection pulse between metal and semiconductor interface for carrier dynamics effects. The objective of this study is to find the quantum mechanics understanding on interface engineering for fabricating the high performance device for future semiconductor technology development. The analysis was carried out with the help of MATLAB. The quantum mechanical spatial field on metal-semiconductor stripe structure have been analyzed by FDTD techniques. This emission reveals a characteristic polar radiation distribution of electric dipoles and a wavelength independent of the structure size or the direction of emission; consequently, it is attributed to thermally generate electric dipoles resonating with the longitudinal optical phonon energy. Phonon energy occur lattice vibration of material by the polarization of light, if the material has rigid structure reflect back the incident light. So, high reflective metal- semiconductor structure always use as photodectors devices in optical fiber communication. No lattice vibration material structure has no phonon effect, so this structure based devices can get high performance any other structure based devices. The transmission and reflection coefficient of metal-semiconductor GaN/Au layer structure compare with GaN/Ti and GaN/Pt structure. Parallel (P) and transverse (S) polarization of light incident on metal-semiconductor nanolayer structure with IR wavelength. Efficient use of the layer by layer (LbL) method to fabricate nanofilms requires meeting certain conditions and limitations that were revealed in the course of research on model systems.