Hot-carrier transport in diamond controlled by femtosecond laser pulses

A laser-induced transient grating technique with femtosecond temporal resolution was used for the study of hot-carrier diffusion and anisotropy of an ambipolar diffusion coefficient in monocrystalline diamond. A hot-carrier transport regime observed at temperatures below 200 K and excited carrier densities lower than 10¹⁶ cm⁻³ persist in the sample 20–30 ps after photoexcitation. Measured drift velocity of hot carriers was approximately 4–8 times higher compared to thermalized carriers. At low sample temperatures and excited carrier densities, the ambipolar diffusion coefficient was found to be anisotropic between <100> and <110> crystallographic directions. We demonstrated experimentally that the carrier energy distribution can be controlled on a sub-picosecond timescale by an additional laser pulse with photon energy below the width of a diamond band gap absorbed by the excited carrier system. Our experimental data were reproduced well by Monte Carlo simulations that confirm the presence of a hot-carrier diffusion regime in diamond. (paper)