Three Temperature Model for Nonequilibrium Energy Transfer in Semiconductor Films Irradiated with Short Pulse Lasers

Abstract

This article investigates numerically carrier-phonon interaction and nonequilibrium energy transfer in direct and indirect bandgap semiconductors during sub-picosecond pulse laser irradiation and also examines the recombination effects on energy transport from the microscopic viewpoint. In addition, the influence of laser fluence and pulse duration is studied by using the self-consistent three-temperature model, which involves carriers, longitudinal optical phonons, and acoustic phonons. It is found that a substantial non-equilibrium state exists between carriers and phonons during short pulse laser irradiation because of time scale difference between the relaxation time and the pulse duration. It is clear that the two-peak structure in carrier temperature exists and it depends mainly on laser pulses, fluences, and recombination processes. During laser irradiation, in particular, the Auger recombination for Si becomes dominant due to the increase in the carrier number density, whereas for GaAs, the Auger recombination process can be ignored due to an abrupt increase in SRH recombination rates at the initial stages of laser exposure.

Femtosecond pulse laser interactions with thin silicon films and crater formation considering optical phonons and wave interference

“…Thorough understanding of heat transfer mechanism and energy transport mechanism from laser-induced materials is of crucial importance for predicting the ablation depth and controlling the resulting modification of the target material in many practical applications such as, micromachining. A lot of efforts have been devoted to the theoretical and experimental studies of the ultrashort laser-solid interactions to reveal the energy transfer mechanism of materials in recent years (Bulgakova et al 2005;Choi and Grigoropoulos 2002;Lee et al 2006;Stoian et al 2002). However, the mechanisms of laser ablation for different materials such as metals, semiconductors, and dielectrics have been still debated and poorly understood for pico-to-femotsecond pulse laser.…”

“…Ultrashort pulse laser ablation provides a promising approach to micro-fabrications of almost any kind of material, because the laser pulses make it possible to deposit a high-density energy into materials in an ultrashort time, so that the effects of heat and laser-plume interactions can be minimized to achieve precise and fine processing (Choi and Grigoropoulos 2002;Lee et al 2006;Stoian et al 2002). Thorough understanding of heat transfer mechanism and energy transport mechanism from laser-induced materials is of crucial importance for predicting the ablation depth and controlling the resulting modification of the target material in many practical applications such as, micromachining.…”

Numerical analysis of crater formation and ablation depth in thin silicon films heated by ultrashort pulse train lasers

“…The variations of carrier number density, electron temperature, and lattice temperature are explained from the viewpoint of some important factors such as pulse duration time, number of pulse, and laser fluence. In fact, the previous 1DTIM cannot intrinsically predict the ablated crater formation of silicon films [7-12, [16][17][18][19][20][21]. Thus, this study extends the previous IDTTM to the two-dimensional model (2DTTM) for the direct comparison with experimental data of the crater shape and depth.…”

“…For the applications listed above, understanding of heat transfer characteristics and energy transport mechanism from laser-induced material is of crucial importance. Extensive efforts have been devoted to theoretical and experimental researches of laser-solid interactions in recent years [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Nevertheless, the mechanisms of laser ablation for different materials 'Corresponding author.…”

“…Many researchers have discussed the ultrashort pulse laser-induced excitation of energy carriers in both electron and lattice systems on the assumption of the local quasi-equilibrium [4-12, [16][17][18][19][20]. The carrier number density, electron temperature, and lattice temperature are estimated on the relaxation time approximation to the Boltzmann transport equation.…”