Using a laser to cool a semiconductor

TL;DR

This paper develops a theoretical model showing how laser irradiation can cool semiconductors by balancing optical absorption and photoluminescence, predicting significant cooling effects in wide bandgap materials like AlN.

Contribution

The paper introduces a nonlocal energy-balance equation for electron and hole temperatures, providing quantitative predictions for laser cooling in semiconductors, which guides future experimental efforts.

Findings

Laser cooling power up to 380 eV/s predicted for AlN.

Cooling efficiency increases with larger bandgap and higher initial temperature.

Electron temperature decreases alongside lattice temperature during cooling.

Abstract

A nonlocal energy-balance equation is derived for the optical absorption, photoluminescence and inelastic electron-phonon scattering, which determines the electron and hole temperatures for any given lattice temperature. The evolution of the lattice temperature is found to be determined by the difference between the power-loss density due to photoluminescence and the power-gain density due to optical absorption, as well as by the initial lattice temperature. We find that in addition to the expected decrease in the lattice temperature, the electron temperature also decreases with time. A laser-cooling power as high as 380 eV/s is predicted for the wide bandgap semiconductor AlN initially at room temperature when the pump-laser field is only 10 V/cm. Laser cooling is found to be more efficient for a large bandgap material, a weaker laser field, and a high initial lattice temperature. The laser-cooling rate then decreases as the lattice cools. The theory presented here provides quantitative predictions that can guide future experiments.