Andreev reflection enhancement in semiconductor-superconductor structures

Abstract

We develop a new theoretical approach for modelling a wide range of semiconductorsuperconductor structures with arbitrary potential barriers and a spatially-dependent superconducting order parameter. We demonstrate asymmetry in the conductance spectrum as a result of a Schottky barrier shape. We further show that Andreev reflection process can be significantly enhanced through resonant tunneling with appropriate barrier configuration, which can incorporate the Schottky barrier as a contributing component of the device. Moreover, we show that resonant tunneling can be achieved in superlattice structures as well. These theoretically demonstrated effects along with our modelling approach enable much more efficient Cooper pair injection into semiconductor-superconductor structures, including superconducting optoelectronic devices.

Two-photon emission from a superlattice-based superconducting light-emitting structure

“…Andreev reflection is described as an inverse process in which an electron enters the superconducting energy gap, forming a Cooper-pair with another electron, resulting in a hole reflected back. The two-particle nature of the Andreev reflection process makes it highly susceptible to variations in the potential landscape (Schottky barrier) and different materials (Fermi velocity mismatch) 46 , as for both particles, the individual transmission coefficients can be reduced. Both the potential landscape and Fermi velocity mismatch often result in inhibition of Andreev reflection in favor of the quasiparticle tunneling regime, manifesting as reduced conductance inside the superconducting gap rather than enhancement.…”

“…Both the potential landscape and Fermi velocity mismatch often result in inhibition of Andreev reflection in favor of the quasiparticle tunneling regime, manifesting as reduced conductance inside the superconducting gap rather than enhancement. In order to increase Cooperpair injection efficiency, bandgap engineering was used and a proper potential landscape was designed 46,47 to support resonant energy levels close to the superconducting interface. When the quasi Fermi energy level is aligned with one of the resonant energy levels, Cooperpair injection probability is expected to increase.…”

Transport across meso-junctions of highly doped Si with different superconductors

“…al. who developed a theoretical model to understand the conductance of Sm-Sc junctions with arbitrary potential barriers 31 . Their results show that due to the presence of the Schottky barrier between the degenerate Sm and the Sc, the process of the retro-reflection of the quasi-particles become non-ideal and hence leads to an asymmetry in the conductance spectra.…”

“…Very recently, a theoretical model also studied the effect of the Schottky barrier present at the Sm-Sc interface. 31 Their results predict asymmetry in the conductance spectra and huge enhancements in the Andreev signal due to resonant tunneling for an appropriate barrier.…”

Andreev Reflection in a Superconducting Light-Emitting Diode

“…On the other hand, wider-bandgap materials emitting in the Si photon counter wavelength range such as AlGaAs, suitable for photon correlation experiments, make Cooper pair injection difficult due to higher Schottky barriers. A promising solution to this trade-off was proposed based on resonant tunneling of Cooper pairs into AlGaAs structures despite higher barriers, enabling future photon correlation experiments. Another interesting direction for future SLED studies can be applying magnetic fields, resulting in effects such as reflectionless tunneling .…”