Enhanced Photon Generation in aNb/n−InGaAs/p−InPSuperconductor/Semiconductor-Diode Light Emitting Device

Abstract

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. DOI: 10.1103/PhysRevLett.107.157403 PACS numbers: 78.60.Fi, 74.25.Gz, 78.66.Fd, 85.60.Jb Recent discoveries of new superconductors [1,2] boosted up the research fields with new experimental as well as theoretical possibilities. From a scientific viewpoint one great advantage of superconductivity is its long coherence time which is the most important feature for quantum information processing [3]. The combined system consisting of a coherent photon field and a superconducting (SC) condensate would be a promising candidate for realizing the quantum operation in solid state devices [4][5][6][7][8]. The Cooper pairs are preserved during these operations with photon energies smaller than the energy gap of superconductivity (on the order of meV). On the other hand, when photon energies become larger than the superconductivity gap, the absorption of high-energy photons only results in the destruction of Cooper pairs. This fact enables the application of superconductors as high-speed singlephoton detectors [9]. It is still unexplored what will take place with the counter process of photon emission from Cooper-pair states in this higher photon energy range.In this Letter, we demonstrate that electron Cooper pairs injected into a semiconductor by the proximity effect [10,11] can be highly involved in the interband transition and accelerate the photon generation processes. We measure the radiative recombination rate as a function of temperature across the SC transition temperature, T C . The results demonstrate drastic enhancement of the radiative recombination rate below T C . The temperature dependence of the radiative recombination rate can be explained by a theoretical model. Our new finding corresponds to experimental demonstration of the Cooper pair's gigantic oscillator strength [12].The light-emitting diode (LED) epitaxial layers were grown on a p-type (001) InP substrate by metalorganic vapor-phase epitaxy. The layers consist of a 500 nm thick p þ À InP buffer layer (Zn doping $1 Â 10 17 cm À3 ), a 30 nm thick n þ À In 0:53 Ga 0:47 As active layer (Si doping $5 Â 10 18 cm À3 ) lattice matched to InP, and a 10 nm thick n þ À In 0:7 Ga 0:3 As Ohmic contact layer (Si doping $5 Â 10 18 cm À3 ). Outside of the contact layer, we attached 20 m wide and 80 nm thick niobium (N...

Proximity-induced high-temperature superconductivity in the topological insulators Bi2Se3 and Bi2Te3

“…This proximity effect has been proposed as a powerful resource for practical applications in optoelectronics 3 and has been predicted to produce the elusive Majorana fermion 4 by combining a superconductor with a topological insulator (TI) [5][6][7][8][9][10] . These goals have been pursued actively, including the recent demonstrations of novel semiconductor light sources 11 and induced superconductivity in TIs [12][13][14][15][16] such as Bi 2 Se 3 and Bi 2 Te 3 , which have been shown to have topologically protected surface states [17][18][19] . Nonetheless, all such experiments performed to date have employed low critical-temperature (low-T c ) materials that require extreme cooling, and the important ratio of the superconducting gap to the Fermi energy in such systems is very small.…”

Time-resolved measurements of Cooper-pair radiative recombination in InAs quantum dots

“…13 We also observed sharp reduction of the LED luminescence decay time constant with another SC-LED below T C , and also demonstrated a good agreement with our theory. 14,15 With these results, we evidenced the active role of Cooper pairs in radiative recombination in SC-LEDs.…”

“…The major term regulating the temperature dependence in this formula is D 2 /T, and the enhancement is proportional to the square of half the SC gap at a given temperature T and inversely proportional to T. 12 We could fit the observed enhancement in the previous SC-LEDs with this analytical formula. [13][14][15]30 The D 2 /T dependence results in more slowly varying temperature dependence than that shown in Fig. 5 and can be approximated for D 0 s 0 /h less than 0.2.…”

“…This also well reproduces our previous observation of decrease of the electroluminescence decay time constant in SC-LEDs. 14,15 These correlations of both the luminescence intensity and the decay time constant to the SC critical temperature are the clear evidence that the observed phenomenon is based on the Cooper-pair recombination in QDs penetrated from the Nb superconductor.…”

Carrier flow and nonequilibrium superconductivity in superconductor-based LEDs

“…In spite of the large mismatch in the energy scale, it is also predicted that the coherence of superconducting pair system can be transferred to photon systems [1][2][3] . The radiative recombination process in superconductor-based LED has been investigated by optical measurements, which revealed the enhanced oscillator strength 4 , high quantum efficiency and radiative recombination time rapidly decreasing with temperature [5][6][7] . In transport measurements, on the other hand, the diffusion of superconducting pairs into the active layer was demonstrated by DC and AC Josephson effect, and the monitoring sensitivity of the radiative recombination process was found to be several orders higher than that in optical measurements although the cause of this ultrahigh sensitivity has not been elucidated 5,6,8 .…”