Electron energy distributions, extending from equilibrium surface states
through transiently populated conduction band states, have been observed in
laser excited silicon by means of transient photoelectron spectroscopy.
Atomically clean (111) wafers in UHV were excited by 90 nsec, 2.33 eV or 65
nsec, 4.66 eV pulses. Photoelectron spectra were obtained with the 4.66 eV
pulses. Photovoltage shifts have been measured and found to saturate. We
have identified a feature in the excited state portion of the spectra due to
electrons which have equilibrated in the conduction band minima (CBM).
Electron temperatures as a function of 2.33 eV pump fluence have been
extracted from the spectra and are shown to be in equilibrium with the
lattice above 1100 K. Very hot non-equilibrium electrons are also observed
to ~ 4 eV above the CBM. A method of determining the diffusion depth of CBM
electrons has been developed and applied to our data.