High-resolution energy analysis of field-assisted photoemission: A spectroscopic image of hot-electron transport in semiconductors

Hot-electron transport in indium phosphide is studied by means of energy-resolved field-assisted photoemission of an Ag/InP Schottky diode. The work function of the thin silver top layer is lowered by cesium and oxygen coadsorption. A quasimonoenergetic electron distribution is created close to the bottom of the conduction band in the bulk of the weakly doped p-type InP crystal by near-band-gap light excitation. The energy-distribution curves of the photoemitted electrons are measured for different values of the bias applied to the Ag/InP contact. It is demonstrated that this set of photoemission spectra constitutes a direct measurement of the evolution of the initial distribution during transport in the high electric field of the band-bending region. From this spectroscopic image of the complex multivalley transport, the relevant energy and momentum relaxation processes are clearly identified. Simple models based on the energy balance between the gain in the electric field and the losses by phonon emission account remarkably well for the experimental results. From the comparison between theory and experiment, the characteristic phonon-scattering times are deduced throughout the first conduction band.