Photoelectric Effect at Sub-Photon Energy in Incident Pulsed Laser Radiation

TL;DR

This paper investigates the photoelectric effect at sub-photon energies in a Ge-on-Si SPAD, showing how constructive interference and bandgap narrowing enable electron excitation with incident pulsed laser radiation.

Contribution

It introduces a classical electrodynamics explanation for sub-photon energy photoelectric effects in heavily doped germanium used in SPADs, highlighting interference effects and bandgap modifications.

Findings

Constructive interference concentrates energy on a single electron.

Sub-photon energy can induce photoelectric effect via field re-emission.

Bandgap narrowing supports energy conservation at sub-photon energies.

Abstract

Photoelectric effect in a Ge-on-Si single-photon avalanche detector (SPAD) at a sub-photon energy in incident pulsed laser radiation is considered in frames of classical electrodynamics of continuous media. It is shown that the energy of incident laser radiation, which is shared among a huge number of electrons in Ge matrix, can concentrate on only one of these through the effect of the constructive interference of the fields re-emitted by surrounding electrons. Conservation of energy in this case is upheld because of a substantial narrowing of the effective bandgap in heavily doped p-Ge, which is used in the design of considered SPAD.