Intrinsic emittance properties of an Fe-doped Beta-Ga2O3(010) photocathode: Ultracold electron emission at 300K and the polaron self-energy

TL;DR

This study investigates ultracold electron emission from Fe-doped beta-Ga2O3(010) photocathodes at 300K, revealing a sub-thermal emission component linked to dopant states and phonon-mediated processes.

Contribution

It provides new insights into the intrinsic emittance properties and emission mechanisms of Fe-doped beta-Ga2O3 photocathodes at room temperature.

Findings

Detected ultracold electron emission with 6 meV MTE at 300K.

Identified two emission processes: direct dopant state emission and phonon-mediated Franck-Condon emission.

Observed spectral trends consistent with polaron self-energy effects in emission behavior.

Abstract

Measurements of the spectral emission properties of an iron-doped a beta-Ga2O3(010) photocathode at 300 K reveal the presence of an ultracold contribution to the total electron beam emission with a 6 meV mean transverse energy (MTE) in the 3.5-4.4 eV photon energy range (282-354 nm). This extreme sub-thermal photoemission signal is consistent with direct emission of electrons photoexcited from the Fe dopant states into the low effective mass and positive electron affinity primary conduction band, and it is superimposed on a stronger signal with a larger MTE associated with an (optical)phonon-mediated momentum resonant Franck-Condon (FC) emission process from a thermally populated and negative electron affinity upper conduction band. For photon energies above 4.5 eV, a transition from a long to a short transport regime is forced by an absorption depth reduction to below 100 nm and both MTE signals exhibit spectral trends consistent with phonon-mediated FC emission if the polaron formation self-energy is included in the temperature of the initial thermalized photoexcited electron distribution.