S. Bin Mansoor

Phonon Transport in Thin Film: Ballistic Phonon Contribution to Energy Transport

Energy transport in dielectric thin films is mainly governed by the phonon transport across the edges of the film. Depending on the phonon frequencies and the film thickness, some of the phonons do not undergo scattering in the film, which results in ballistic effect on the energy transport in the film. In the present study, the influence of ballistic phonons on the energy transport in silicon thin film is investigated for a spatially varying temperature source at the film edge. The Gaussian temperature distribution at one edge of the film is considered to account for the spatial variation of temperature. The influence of film thickness on energy transport is also incorporated in the analysis. It is found that the Gaussian parameter, defining the spatial distribution of temperature at the film edge, significantly influences equivalent equilibrium temperature variation in the film. Equivalent equilibrium temperature reduces sharply across the film as the film thickness reduces.

Transient Effects of Phonon Transport in Two-Dimensional Silicon Film

Energy transport in silicon film takes place through a phonon transport, which is important in cooling applications of photonic devices. Since the energy transport is transient, the transient effect should be considered in the analysis. In the present study, phonon transport in the two-dimensional silicon film with transient effect is considered. The Boltzmann transport equation is solved numerically with the appropriate boundary conditions to compute equivalent equilibrium temperature in the film. The difference between equivalent equilibrium temperature in one- and two-dimensional films is demonstrated, and the time required to attain a steady state temperature in the film is established. The findings revealed that the time required to reach steady temperature is faster in the vicinity of the high temperature edge of the film than that corresponding to the low temperature edge. Equivalent equilibrium temperature for one-dimensional film is slightly lower than its counterpart corresponding to two-dimensional film during the time period t ≤ 30 ps; however, as the heating period progresses, this becomes the opposite.

Lattice Phonon and Electron Temperatures in Silicon-Aluminum Thin Films Pair: Comparison of Boltzmann Equation and Modified Two-Equation Model

Phonon and carrier transport in silicon-aluminum film pairs is examined. The energy transport equation for electrons and lattice subsystems for aluminum film is derived from the Boltzmann equation. Equivalent equilibrium temperature for lattice phonons and electrons are computed across the silicon and aluminum film. Reflection and transmittance of phonons at the silicon interface are considered to account for the thermal boundary resistance. The influence of film thickness on equivalent equilibrium temperature is also examined. Electron and lattice phonon temperature predictions are compared with their counterparts obtained from the modified two-equation model for the aluminum film. It is found that the solution of Boltzmann equation predicts slightly higher temperature at the silicon interface than that of the modified two-equation model. The nonlinear behavior of lattice phonon temperature at the aluminum interface extends toward the aluminum film with increasing film thickness.

Laser Short-Pulse Interaction of Aluminum and Silicon Films

In the present study, laser short-pulse heating of an aluminum film surface which is attached to a silicon film is examined. The two-equation model including the phonon diffusion is used to determine electron and phonon temperatures in the aluminum film while radiative phonon transport is incorporated to determine equilibrium temperature in the silicon film. Since electron diffusion from the aluminum film interface to the silicon film interface doesnottakeplace,onlythephonontransportisconsideredacrosstheinterface.Thethermalboundaryresistanceat the interface is incorporated in the analysis. The transfer matrix method is used to determine the photon absorption in the aluminum film due to the laser irradiation pulse. It is found that phonon temperature decays sharply in the aluminum film toward the interface due to the presence of the thermal boundary resistance. The reflected radiative phonons from the back surface of the silicon film modify temperature distribution in the neighborhood of the silicon film interface.

Temperature Distribution in Silicon-Aluminum Thin Films with Presence of Thermal Boundary Resistance

Phonon transport in two-layer films, consisting of silicon and aluminum, is considered. Phonon radiative energy transfer is incorporated to predict equilibrium temperature distribution in the silicon film, while the modified two-equation model is used to predict electron and phonon temperatures in the aluminum film. The thermal boundary resistance is introduced at the interface of both films. Equilibrium temperature decay is found to be sharp in the early heating period in the silicon film. Phonon temperature remains higher than electron temperature in the vicinity of the interface of aluminum film. Electron and phonon temperature become the same at mid-thickness of the aluminum film.