M.Sc Thesis

M.Sc StudentStrugo Nir
SubjectSuperconductor-Semiconductor Waveguide Devices
DepartmentDepartment of Electrical and Computer Engineering
Supervisor ASSOCIATE PROF. Alex Hayat
Full Thesis textFull thesis text - English Version


Integration of the unique quantum phenomena of superconductors with the well-established solid-state characteristics of semiconductors has opened new interdisciplinary research fields, such as superconducting optoelectronics, where light interacts with superconductor-semiconductor hybrid structures.

One of the promising ideas that arose from this field is the superconducting two-photon gain (STPG). In STPG, superconducting Cooper-pairs, injected into the semiconductor using the proximity effect, recombine with normal holes as part of a fully stimulated two-photon emission process in a waveguide structure. STPG enables new directions in fundamental physics as well as in quantum technologies, owing to its potential for highly efficient two-photon amplification process, comparable to the first-order process of one-photon gain with merely picojoule-scale seed energy pulse. Nevertheless, practical aspects of its realization have not been studied before.

In this study, we harness superconductivity along with plasmonic phenomena to adapt and enable an enhanced version of the two-photon gain process, being utilized in various fields of science and technology, for modern nanoscale devices.

As Cooper-pair based gain active region is restricted to the superconductor-semiconductor interface, it limits the two-photon gain process potential. Especially in conventional dielectric waveguide structures, due to the small overlap with their transverse mode, characterized by a peak intensity far from the superconductor interface. By using the superconductor layer as part of a plasmonic waveguide structure, in addition to being the Cooper-pair source, we theoretically demonstrate three-orders of magnitude enhancement of the STPG coefficient, due to photon confinement, in comparison with the superconductor-based dielectric waveguide structure. We further study the effects of carrier concentration levels on the waveguide transverse modal power confinement in the Cooper-pair based active-region and the modal gain parameters. Showing that STPG produced in a plasmonic waveguide increases with carrier concentration and hence meets practical device requirements.

Aiming to provide evidence and measurements of the STPG process, an experiment was conducted with preliminary results. Devices for the experiment were prepared as Nb based plasmonic waveguides, on top of an In0.53Ga0.47As PN-junction stack with heavily doped n-type layer. A femto-second pulsed laser source was used to excite the plasmonic modes via various grating coupler nano-patterns that were engraved in the Nb with focused ion-beam. Using confocal optical system with high magnification and near diffraction-limit spot illumination, the desired surface plasmon polariton mode on the Nb-InGaAs interface was observed.

Our results pave the way for realization of efficient two-photon amplification in nanoscale devices and offer opportunities in the fields of pulse design, nonlinear photonics and quantum optics.