Dielectric Phonon Research Articles

Plasmon-phonon resonance at gate-electrode/gate-dielectric interface on carrier mobility of organic TFTs with high-k gate dielectrics

The resonance between the plasmons in gate electrode and the phonons in gate oxide of the omnipresent metal–oxidesemiconductor devices predicted in 2004 is experimentally demonstrated to degrade the mobility of the carriers in the semiconductor channel. By using bottom-gated pentacene organic thin-film transistors fabricated on n-type Si substrates with different resistivities, this work experimentally shows that even for thick HfLaO gate dielectric (~50 nm), the interaction between the gate plasmons and the dielectric phonons can significantly affect the carrier mobility. FTIR and Raman spectra reflect that the phonon frequency of the dielectric ranges from 13.2 to 24.9 THz, overlapping the gate-plasmon frequency (13.2 ~ 18.7 THz) of the 0.01 ~ 0.015 Ω·cm substrate. Therefore, the predicted mobility reduction can be explained by a simpler concept of “resonance”: when the oscillations of gate carrier and dielectric atom have about the same frequency, the remote phonon scattering of the gate dielectric on the channel carriers is greatly enhanced to reduce their mobility. In summary, this resonance-induced mobility reduction could pose a temperature-related reliability problem to electronic circuits when carrier freeze-out at low working temperature reduces the carrier density in the gate electrode to about 3 × 1018 cm−3 to result in a plasmon frequency close to the phonon frequency of the gate dielectric.

Modulation of the probe signal in coherent phonon detection revisited: Analytical and first-principles computational analyses

Modulation of probe signal in pump-probe measurements of coherent phonons in dielectrics, with and without spectral resolution, are investigated theoretically taking diamond as an example. Analytical investigation as well as first-principles calculations based on time-dependent density functional theory is utilized to clarify the mechanism of the modulation of the probe signals. Boundary and bulk effects are investigated systematically, putting emphasis on the phase relation between the modulation and the atomic motion of the coherent phonon. They are summarized as follows: Modulation by the boundary effect is in phase with the coherent phonon amplitude, while that by the bulk effect shows $\pi/2$ phase difference. Strong frequency dependence appears in the modulation by the bulk effect, while no frequency dependence by the boundary effect. First-principles calculations support the reliability of the analytical result.

Influence of the electron–phonon interfacial conductance on the thermal transport at metal/dielectric interfaces

Thermal boundary conductance at a metal-dielectric interface is a quantity of prime importance for heat management at the nanoscale. While the boundary conductance is usually ascribed to the coupling between metal phonons and dielectric phonons, in this work we examine the influence of a direct coupling between the metal electrons and the dielectric phonons. The effect of electron–phonon processes is generally believed to be resistive and tends to decrease the overall thermal boundary conductance as compared to the phonon–phonon conductance σp. Here, we find that the effect of a direct electron-phonon interfacial coupling σe is to enhance the effective thermal conductance between the metal and the dielectric. Resistive effects turn out to be important only for thin films of metals that have a low electron–phonon coupling strength. Two approaches are explored to reach these conclusions. First, we present an analytical solution of the two-temperature model to compute the effective conductance which accounts for all the relevant energy channels, as a function of σe, σp and the electron–phonon coupling factor G. Second, we use numerical resolution to examine the influence of σe on two realistic cases: a gold film on silicon or silica substrates. We point out the implications for the interpretation of time-resolved thermoreflectance experiments.

Theory of suppressing avalanche process of carrier in short pulse laser irradiated dielectrics

A theory for controlling avalanche process of carrier during short pulse laser irradiation is proposed. We show that avalanche process of conduction band electrons (CBEs) is determined by the occupation number of phonons in dielectrics. The theory provides a way to suppress avalanche process and a direct judgment for the contribution of avalanche process and photon ionization process to the generation of CBEs. The obtained temperature dependent rate equation shows that the laser induced damage threshold of dielectrics, e.g., fused silica, increase nonlinearly with the decreases of temperature. Present theory predicts a new approach to improve the laser induced damage threshold of dielectrics.

A Physical Model of the Temperature Dependence of the Current Through $\hbox{SiO}_{2}\hbox{/}\hbox{HfO}_{2}$ Stacks

In this paper, we investigate the characteristics of the defects responsible for the leakage current in the SiO2 and SiO2/HfO2 gate dielectric stacks in a wide temperature range (6 K-400 K). We simulated the temperature dependence of the I -V characteristics both at positive and negative gate voltages by applying the multiphonon trap-assisted tunneling model describing the charge transport through the dielectric. In the depletion/weak inversion regime, the current is limited by the supply of carriers available for tunneling. In strong inversion, the temperature dependence is governed by the charge transport mechanisms through the stacks; in particular, in SiO2/HfO2 dielectric stacks, the coupling of the injected carriers with the dielectric phonons at the trap sites is the dominant mechanism. Matching the simulation results to the measurement data allows extracting important trap parameters, e.g., the trap relaxation and ionization energies, which identify the atomic structure of the electrically active defects in the gate dielectric.

Dynamical model for S N2 reactions in solution. The Cl −+CH 3Cl → ClCH 3 + Cl − reaction

A dynamical model for chemical reactions in solution is described. A reacting system and a larger number of solvent molecules are enclosed within a spherical cavity. The molecular reaction dynamics is followed by solving the classical equations of motion of the molecular system within the cavity. The cavity is immersed into a dielectric phonon medium. The rate constant is estimated to be about 3.0 X 10 −30 cm 3/s at room temperature.

Ferroelectricity and coherent phonon generation in piezoelectric composition-modulated structures

In this paper we suggest an approach to making new metastable ferroelectric materials and piezoelectric transducers which should be efficient in generating coherent phonons with wavelengths approaching interatomic distances. This involves the fabrication of composition-modulated (layered) structures consisting of piezoelectric components. The coherency strain accompanying short wavelength composition modulation leads to ferroelectricity; the periodic modulation of the piezoelectric parameters leads to an anomalously strong coupling to far infrared light when the composition wavelength is an odd half-multiple of the wavelength of a phonon at the driving frequency. Such transducers can open a new dimension in the study of phonons in dielectrics at low temperatures.