Polariton refrigerator could chill tiny semiconductor devices
Physics World, May 15, 2015. Image credit: geralt
A new method for using light to cool solids has been created by physicists in France and Germany. The technique uses quasiparticles called “polaritons” to remove vibrational heat from a tiny piece of semiconductor, and unlike previous optical cooling schemes it works at very low temperatures. The scheme could provide a new way of cooling very small electronic devices, as well as giving physicists an alternative approach to studying heat transport.
The new variant of ASF gets round this problem by not using excitons but polaritons, which form when photons interact strongly with excitons. The technique involves confining the polaritons within a semiconductor microcavity, which is essentially a semiconductor material sandwiched between two semi-transparent mirrors. This confinement imposes a non-zero minimum energy on the polariton, which means that it cannot decay via phonons alone.
The polariton can then undergo one of two cooling interactions with phonons. “Fast cooling” involves the absorption of one phonon followed by the emission of an ASF photon and is so-called because it happens in about 1 ps. The “slow cooling” interaction takes about 200 ps and begins with absorption of a phonon, then the emission of a lower-energy phonon and finally an ASF photon. Although some heat is returned to the semiconductor during slow cooling, the net cooling effect is actually greater than with fast cooling.