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

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.

Femtosecond Two-Photon Laser Photoelectron Microscopy

“…The observed photocurrent, just as for the diamond and the calcium fluoride cases, depended quadratically on the irradiation intensity I . The absolute value of a coefficient of two-photon external photoelectric effect yield β 2 (for the wavelength of 410 nm, averaged) was measured to be 1.5 × 10 -32 cm 2 s. Such a value corresponds well with the known value of an analogous coefficient for the wavelength of 355 nm: β 2 = 2.5 × 10 -32 cm 2 s …”

“…Coefficient β 2 is in the same range as other known values of two-photon photoelectric effect yield coefficients from semiconductors and dielectrics. − Our approach has an additional advantage in comparison with the other “classic” methods of measuring an external photoelectric effect yield, because we measure not only the averaged value of the β 2 coefficient but its local values (with a spatial resolution on the order of 30−40 nm or even better) as well. It should be noted that we neglected the reflection of light from the surface studied and the variation of the angle of the light incidence when calculating the β 2 value, but such a neglect is typical for all methods of two-photon external photoelectric effect yield coefficient measurements. − …”