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We report ultrafast surface pump and interface probe experiments onphotoexcited carrier transport across single crystal bismuth films on sapphire.The film thickness is sufficient to separate carrier dynamics from latticeheating and strain, allowing us to investigate the time-scales of momentumrelaxation, heat transfer to the lattice and electron-hole recombination. Themeasured electron-hole ($e-h$) recombination time is 12--26 ps and ambipolardiffusivity is 18--40 cm$^{2}$/s for carrier excitation up to $\sim 10^{19}\text{cm}^{-3}$. By comparing the heating of the front and back sides of thefilm, we put lower limits on the rate of heat transfer to the lattice, and byobserving the decay of the plasma at the back of the film, we estimate thetimescale of electron-hole recombination. We interpret each of these timescaleswithin a common framework of electron-phonon scattering and find qualitativeagreement between the various relaxation times observed. We find that thecarrier density is not determined by the $e-h$ plasma temperature after a fewpicoseconds. The diffusion and recombination become nonlinear with initialexcitation $\gtrsim 10^{20} \text{cm}^{-3}$.

Free-carrier relaxation and lattice heating in photoexcited bismuth thin films