Time-resolved thermionic and photoemission from nanosecond, pulsed laser excited germanium and silicon

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Abstract
We report electron emission from (111) surfaces of intrinsic crystalline Ge and Si using 25-ns laser pulses at λ=1.06, 0.53, 0.35, and 0.26 μm. For 0.26 and 0.35 μm, two-photon photoemission is observed, while for 0.53 and 1.06 μm only thermionic emission is obtained. In all cases the emission current follows the temporal profile of the laser pulse up to the melting point. Analysis of the thermionic data, taking account of the nonequilibrium carrier density, indicates that the electron temperature follows, but can be up to several hundred degrees higher than, the lattice temperature, during the laser pulse.