A Cooper-Pair Light-Emitting Diode: Temperature Dependence of Both Quantum Efficiency and Radiative Recombination Lifetime

A light-emitting diode (LED) in the optical-fiber communication band showed special features after replacing the n-type electrode with niobium (Nb) superconducting metal. Nb electrodes prepared on an InGaAs-based semiconductor surface formed a superconductor/semiconductor/superconductor junction, and the current-voltage characteristics exhibited both DC and AC Josephson junction properties. This was a result of the injection of electron Cooper-pairs into the n-InGaAs active layer of an LED. The drastic enhancement of the electroluminescence output observed below the Nb superconducting critical temperature, $T_{\text{c}}$, demonstrates the active role of electron Cooper-pairs in radiative recombination. Lifetime measurements of this LED and accurate evaluation of the luminescence output made it possible to estimate the radiative recombination lifetimes. A theoretical formula derived for the Cooper-pair radiative recombination accurately describes both the measured steep reduction of the radiative recombination lifetime and the observed enhancement of the internal quantum efficiency below $T_{\text{c}}$. This work will assist the development of interdisciplinary physics and new applications in superconductivity and optoelectronics.