Laser cooling based on nitride structures

Laser cooling of solids based on anti-Stokes photoluminescence was proposed in 1929 [1]. Indeed, through the light emission based on phonon-assisted anti-Stokes photoluminescence, the average photon energy emitted is larger than that for the absorbed pump photons. The difference between the emitted and absorbed photon energies is made up by the energy of each removed phonon. Since phonons represent collective excitation in solids, the temperature of a material is reduced through the anti-Stokes photoluminescence. Such a concept for laser cooling was realized in ytterbium-doped glass [2]. Nowadays, laser cooling using rare-earth doped materials approaches a cryogenic temperature [3], which has already exceeded the performance of a typical thermoelectric cooler. However, it would be more practical if laser cooling can be implemented in a semiconductor material. A laser-cooling device based on a semiconductor material can be readily integrated with semiconductor devices from high electron mobility transistors to laser diodes. Moreover, it has a potential for reaching much lower temperatures.