Enhanced Photon Generation in a $\mathrm{Nb}/n-\mathrm{InGaAs}/p-\mathrm{InP}$ Superconductor/Semiconductor-Diode Light Emitting Device

We experimentally demonstrate Cooper pairs’ drastic enhancement of the band-to-band radiative recombination rate in a semiconductor. Electron Cooper pairs injected from a superconducting electrode into an active layer by the proximity effect recombine with holes injected from a $p$-type electrode. The recombination of a Cooper pair with $p$-type carriers dramatically increases the photon generation probability of a light-emitting diode in the optical-fiber communication band. The measured radiative decay time rapidly decreases with decreasing temperature below the superconducting transition temperature of the niobium electrodes. Our results indicate the possibility to open up new interdisciplinary fields between superconductivity and optoelectronics.

Figure 1

Cooper-pair LED and measurement setup: (a) Schematic illustration of the LED structure and measurement setup of the $I\mathrm{\text{−}}V$ and EL properties. (b) Optical-microscope picture of the LED surface and the expanded secondary-electron-microscope picture of the slit formed in the niobium (Nb) electrode. (c) Schematic diagram of electron Cooper-pair injection from the surface Nb electrodes to the $p\mathrm{\text{−}}n$ junction, which recombine with holes in the valence band injected with the higher forward bias of the $p$ electrode.

Figure 2

Current-voltage characteristics of the $\mathrm{Nb}/n-\mathrm{InGaAs}/\mathrm{Nb}$ junction on the LED surface measured at 30 mK. The inset data were measured at 16 GHz; however, the Shapiro step intervals change with $\Delta V=2.1\mu \mathrm{V}/\mathrm{GHz}$ by changing the RF. The $I\mathrm{\text{−}}V$ characteristics with the different forward bias are all offset by $100\mu \mathrm{V}$ for clarity.

Figure 3

(a) EL spectrum measured at 4 K with constant injection current. (b) Transient decay of the spectrally integrated EL intensity: the diode bias set to the ON state is stepwise changed to the OFF state at 0 ns. The measured transient EL decay is shown in the inset with the offset bias of zero and 600 mV shown with solid (black) triangles and open (blue) circles, respectively. The solid lines are the model fitting. The intrinsic EL transients restored from the measured data are shown for 3 and 10 K.

Figure 4

(a) Temperature dependence of the measured LED decay time, ${\tau }_{\mathrm{LED}}$ [solid (red) circles]; note that the larger error bar at the 0.8 K point is due to the limited measurement time because of heating of the current-driven LED device at the lowest temperatures and the conversion of the cryostat operation mode. The solid (red) line is the fit with Eq. (2). Open (blue) triangles show ${\tau }_{\mathrm{rad}}$ of a reference LED device with the electrode material exchanged from Nb to normal metal (Au); the dashed (blue) line is a guide to the eye. (b) The resistance [solid (green) circles] measured along the Nb electrode indicates $T_{\mathrm{C}}=7.3\mathrm{K}$; the integrated EL intensity [open (blue) circles] during the ON-state shows a temperature independent behavior.