Evidence of Refrigerating Action by Means of Photon Emission in Semiconductor Diodes

Abstract

More than 90% of the photons emitted from forward-biased GaAs diodes have energies $h\ensuremath{\nu}$ higher than the applied voltage $V$. Thus, a portion of the energy of these photons must come from lattice heat. This portion is 3% of $h\ensuremath{\nu}$ for photons at the peak of the incoherent emission spectrum. An upper limit of ($h\ensuremath{\nu}\ensuremath{-}qV$) is estimated from thermodynamics. This difference is larger at 78 than 27\ifmmode^\circ\else\textdegree\fi{}K, in agreement with theory. Also, the dependence of the effect on voltage and current is in fair agreement with expectations. At high forward currents, near the threshold for stimulated emission, $h\ensuremath{\nu}$ is about equal to $\mathrm{qV}$. The removal of heat, in the form of photon energy from the crystal, should in principle lead to refrigeration. The main requirement for net cooling is a quantum efficiency (photons/electron) higher than 0.97. At 10 mA, with an assumed quantum efficiency of 0.99, the heat removal rate (per diode) is estimated as 3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$ W compared to a Joule heating rate of 5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}5}$ W.