Multi-phonon-assisted absorption and emission in semiconductors and its potential for laser refrigeration

TL;DR

This paper develops a theory of multi-phonon-assisted processes in semiconductors to evaluate their potential for laser cooling, highlighting CdS as a promising candidate due to its phonon properties.

Contribution

It introduces a simple theoretical model for multi-phonon-assisted absorption and emission in wide-gap semiconductors, comparing materials like GaN, CdS, and GaAs for laser cooling potential.

Findings

CdS shows promising laser cooling prospects due to strong electron-phonon coupling.

Large phonon energy in GaN may limit its effectiveness for laser cooling.

The theory helps identify suitable wide-gap semiconductors for laser refrigeration.

Abstract

Laser cooling of semiconductors has been an elusive goal for many years, and while attempts to cool the narrow gap semiconductors such as GaAs are yet to succeed, recently, net cooling has been attained in a wider gap CdS. This raises the question of whether wider gap semiconductors with higher phonon energies and stronger electron-phonon coupling are better suitable for laser cooling. In this work we develop a straightforward theory of phonon-assisted absorption and photoluminescence of semiconductors that involves more than one phonon and use to examine wide gap materials, such as GaN and CdS and compare them with GaAs. The results indicate that while strong electron-phonon coupling in both GaN and CdS definitely improves the prospects of laser cooling, large phonon energy in GaN may be a limitation, which makes CdS a better prospect for laser cooling.