Macroscopic electron-hole distribution in silicon and cubic silicon carbide by the intense femtosecond laser pulse

T Otobe

doi:10.1063/1.5124424

Abstract

Electron excitations at silicon and cubic silicon carbide (3C-SiC) surfaces caused by an intense femtosecond laser pulse are calculated by solving the time-dependent density functional theory and Maxwell’s equation simultaneously. The energy absorption, carrier density, and electron-hole quasitemperatures decrease exponentially in 100 nm from the surface. The electron and hole quasitemperatures have finite values even at large distances from the surface because of a specific photoabsorption channel. Although the quasitemperature in the silicon shows a smooth exponential decrease, 3C-SiC shows the stepwise decrease because of the change of concerning bands. The quasitemperature depends not only on the excitation process, i.e., tunnel and multiphoton absorption, but also on the band structure significantly.

Highlights

IntroductionThe precise description of the electron-hole distribution and their quasitemperatures is important to understand the initial stage of laser processing
Processing of solid materials using femtosecond laser pulses has attracted considerable interest for potential applications in the high-precision processing technology.[1–12] Because a femtosecond laser pulse can deposit large amounts of energy into solid materials within a much shorter time than the conventional spatial diffusion of thermal energy to the exterior of the irradiated spot, we can process materials with small thermal denaturation outside of the irradiated volume.[10,11]The precise description of the electron-hole distribution and their quasitemperatures is important to understand the initial stage of laser processing
We found that the quasitemperature and the electron-hole distribution depend on the excitation process

Summary

Introduction

The precise description of the electron-hole distribution and their quasitemperatures is important to understand the initial stage of laser processing. The multiphoton absorption and tunnel excitation processes are the crucial electron excitation processes in semiconductors under the femtosecond laser pulse. Since these processes are nonlinear and/or nonperturbative, we have to treat the dynamics of the electron and electromagnetic fields simultaneously.[13,14]. The two-temperature model[15,16] (TTM) is a common approach to describe the energy flow between an electron and phonon in metals. The electron excitation process and electron-hole distribution is complicated, the excitation process and the estimation of the electron temperature assume the simple model with the Fermi-Dirac distribution and Keldysh theory.[32]

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Conclusion