High Quantum Efficiency Ultrananocrystalline Diamond Photocathode: Negative Electron Affinity Meets $n$-doping

TL;DR

This study demonstrates a nitrogen-incorporated ultrananocrystalline diamond photocathode with high quantum efficiency enabled by negative electron affinity and n-doping, showing promising results for UV and visible light photoemission.

Contribution

It introduces a novel (N)UNCD:H photocathode combining NEA and n-doping, achieving measurable QE in UV and visible spectra, advancing diamond-based photocathode technology.

Findings

QE of ~0.1% at 254 nm

Visible light sensitivity with QE of ~5×10^{-8} at 405 nm

Surface stability against air exposure due to H-termination

Abstract

We report results of quantum efficiency (QE) measurements carried out on a 150 nm thick nitrogen-incorporated ultrananocrystalline diamond terminated with hydrogen; abbreviated as (N)UNCD:H. (N)UNCD:H demonstrated a QE of $\sim$10$^{-3}$ ($\sim$0.1%) at 254 nm. Moreover, (N)UNCD:H was sensitive in visible light with a QE of $\sim$5$\times$10$^{-8}$ at 405 nm and $\sim$5$\times$10$^{-9}$ at 436 nm. After growth and prior to QE measurements, samples were exposed to air for about 2 hours for transfer and loading. Such design takes advantage of a key combination: 1) H-termination inducing negative electron affinity (NEA) on the (N)UNCD and stabilizies its surface against air exposure; and 2) N-incorporation inducing $n$-type conductivity in intrinsically insulating UNCD.