Spectral Emission Properties of a Nitrogen-doped Diamond(001) Photocathode: Hot Electron Transport and Transverse Momentum Filtering

TL;DR

This study investigates the spectral emission properties of nitrogen-doped diamond(001) photocathodes, revealing anomalous trends in electron emission linked to hot electron transport, band structure, and momentum filtering effects.

Contribution

It provides a detailed analysis of the electron emission mechanisms in nitrogen-doped diamond photocathodes, highlighting the role of hot electron transport and transverse momentum filtering.

Findings

Spectral trends of mean transverse energy and quantum efficiency are anomalous and non-monotonic.

Hot electron emission is restricted parallel to the surface due to low transverse effective masses.

Emission characteristics are consistent with known diamond physics and electron-phonon interactions.

Abstract

The electron emission properties of a single-crystal nitrogen-doped diamond(001) photocathode inserted in a 10kV DC photoelectron gun are determined using a tunable (235-410nm) ultraviolet laser radiation source for photoemission from both the back nitrogen-doped substrate face and the front homo-epitaxially grown and undoped diamond crystal face. The measured spectral trends of the mean transverse energy (MTE) and quantum efficiency (QE) of the emitted electrons are both anomalous and non-monotonic, but are shown to be consistent with (i) the known physics of electron photoexcitation from the nitrogen substitution states into the conduction bands of diamond, (ii) the energy position and dispersion characteristics of the conduction bands of diamond in the (001) emission direction, (iii) the effective electron affinity of the crystal faces, (iv) the strong electron-(optical)phonon coupling in diamond, and (v) the associated hot electron transport dynamics under energy equipartition with the optical phonons. Notably, the observed hot electron emission is shown to be restricted parallel to the photocathode surface by the low transverse effective masses of the emitting band states - a transverse momentum filtering effect.