Fowler-Nordheim-like local injection of photoelectrons from a silicon tip

TL;DR

This study investigates tunneling of photoelectrons from a silicon tip to a gold surface, revealing a Fowler-Nordheim-like process for conduction band electrons and analyzing the effects of bias, distance, and light intensity.

Contribution

It demonstrates a Fowler-Nordheim-like tunneling mechanism for photoelectrons from silicon tips, extending understanding of photoelectron injection at the nanoscale.

Findings

Photoelectron tunneling follows a Fowler-Nordheim-like process.

Bias dependence matches theoretical models including image charge effects.

Fluctuations are linked to oxide layer modifications.

Abstract

Tunneling between a photo-excited p-type silicon tip and a gold surface is studied as a function of tip bias, tip/sample distance and light intensity. In order to extend the range of application of future spin injection experiments, the measurements are carried out under nitrogen gas at room temperature. It is found that while tunneling of valence band electrons is described by a standard process between the semiconductor valence band and the metal, the tunneling of photoelectrons obeys a Fowler-Nordheim-like process directly from the conduction band. In the latter case, the bias dependence of the photocurrent as a function of distance is in agreement with theoretical predictions which include image charge effects. Quantitative analysis of the bias dependence of the dark and photocurrent spectra gives reasonable values for the distance, and for the tip and metal work functions. For small distances image charge effects induce a vanishing of the barrier and the bias dependence of the photocurrent is exponential. In common with many works on field emission, fluctuations in the tunneling currents are observed. These are mainly attributed to changes in the prefactor for the tunneling photocurrent, which we suggest is caused by an electric-field-induced modification of the thickness of the natural oxide layer covering the tip apex.