Superconducting Effect on Radiative Recombinations in Long-wavelength Light Emitting Diode

Abstract

Application fields of light emitting diodes (LEDs) are expanding in various fields. Development of LED-based single photon sources is expected to open a new possibility to expand the applications to quantum information communication and processing. The authors have proposed a photon-emitting LED combined with superconducting electrodes, which is expected to be an on-demand entangled photon pair source [1]. The main mechanism is based on the coherent spatial extension of the Cooper-pair states to the photon emitting layer, which is expected to enhance the oscillator strength of the radiative recombination processes by the Cooper-pair superradiance effect [2]. The preliminary operation was demonstrated with InGaAs quantum well (QW) LEDs and about 20-times enhancement of the electroluminescence (EL) was observed under the low-injection current regime [3]. This is the demonstration of the improved internal quantum efficiency (QE) under the low internal QE operation of the LED. In this paper, the enhancement of the radiative recombination processes with the superconducting (SC) effect is demonstrated by the lifetime measurements under the operation with high (~100%) internal quantum efficiency (QE).Electron Cooper pairs are injected into p-n junctions of n-InGaA/p-InP LEDs from Nb SC n-type electrodes [1] and will recombine with hole pairs injected from the p-side of LEDs. EL was observed from a Nb slit formed in the Nb electrode with the ~100-nm width. The main emission peak is around 1450nm at the measured temperature range of 2~12K. The SC critical temperature, Tc, of the Nb electrode was measured to be 7.3K in this sample. The diode built-up voltage remained low around 1.2V even at the low measurement temperature. The EL integrated intensity was linearly increased with the CW injection current and was temperature independent below and above the Nb Tc. This shows that the EL emission is dominated by the radiative recombination in this LED. The LED pulsed operation was measured with newly developed Hamamatsu Photonics Infrared StreakCamera. Consistent with the CW measurements, the EL intensity measured with the pulsed injection current of 1.6mA during the pulse duration was almost constant and was independent of the temperature, demonstrating the high internal QE. However, the recombination lifetime measured from the EL transient decay showed the critical temperature dependence below the Nb SC Tc of 7.3K. It was reduced from the constant value of ~1.9ns above 7.3K to 1.3ns at 1K. This shows that the radiative recombination lifetime is reduced below 7.3K, demonstrating the enhanced radiative recombinations with the SC effect, i.e., Cooper-pair superradiance effect. Since single photon emitters are usually operated under low injection currents where internal QE tends to be low, this new mechanism is extremely useful to realize on-demand photon emitting LEDs.This work was supported in part by the HINTS for nanofabrication. They are also grateful for all the collaborators related to this work.

Proximitized Josephson junctions in highly-doped InAs nanowires robust to optical illumination

“…4 Experimentally, enhanced photon generation in light-emitting diodes based on conventional epitaxially-grown semiconductor p-n junctions contacted by superconducting leads have been demonstrated. 5 Semiconducting nanowires constitute an important building block for hybrid devices relying on superconducting electrodes and the proximity effect, which was employed for the demonstration of gate-tunable Josephson junctions, 6 quantum electron pumps 7 and microwave quantum circuits. 8 In particular, hybrid nanowire devices are extensively studied due to the promising prospects for topological quantum computing mediated by Majorana zero modes.…”