Download Germanium based superconducting tunnel junctions for low-temperature cooling

Title
Germanium based superconducting tunnel junctions for low-temperature cooling
Description
Superconducting tunnel junctions (STJs) have been demonstrated in the past to cool platforms
which are intended to support applications such as quantum computers and optical detectors that need
to operate in the sub-Kelvin regime for enhanced signal to noise. These STJs take advantage of the
weak electron-phonon coupling in normal metals (and degenerate semiconductors) at very low
temperatures to thermally decouple the electronic system from the lattice. By applying a small bias
across the structure, the superconductor bandgap can be used to filter out “hot electrons” which will
lower the overall temperature of the electrons in the normal metal (or degenerate semiconductor) part
of the refrigeration elements. By connecting these coolers to an otherwise isolated platform heat can be
extracted from the application package, all at the flick of a switch.
Most STJs that have been used for this application have been in the form of a Normal metal /
Insulator / Superconductor (NIS) junction on an insulating membrane. However, these junctions have a
counterpart in the Semiconductor – Superconductor (SmS) Schottky junctions, which may allow
commercial silicon and germanium integrated circuitry (IC) to be integrated into these cooling
platforms.
We have recently reported on the effectiveness of these cooling platforms using epitaxially grown
bulk silicon and strained silicon [1,2]. In contrast to silicon, germanium shows a potential to
outperform its predecessor. The aim of this project would be to develop and research germanium based
STJs for cooling applications, with the possibility of placing STJ devices on mirco-electro-mechanical
systems (MEMS) structures. The project will involve structural characterization of materials by a
variety of in-house, cutting edge experimental techniques including Transmission Elecron Microscopy
(TEM), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and X-ray
diffraction; fabrication of micro- and nano-scale devices using in-house optical and Focused Ion Beam
(FIB) lithography, deposition and etching techniques; and low-temperature electrical, Hall effect and
thermoelectric measurements of the devices.
1.
2.
J.T. Muhonen, M. J. Prest, M. Prunnila, D. Gunnarsson, V. A. Shah, A. Dobbie, M. Myronov, R. J. H.
Morris, T. E. Whall, E. H. C. Parker and D. R. Leadley "Strain dependence of electron-phonon energy loss
rate in many-valley semiconductors." Applied Physics Letters 98(18) 182103 (2011).
M.J. Prest, J. T. Muhonen, M. Prunnila, D. Gunnarsson, V. A. Shah, J. S. Richardson-Bullock, A. Dobbie,
M. Myronov, R. J. H. Morris, T. E. Whall, E. H. C. Parker and D. R. Leadley "Strain enhanced electron
cooling in a degenerately doped semiconductor." Applied Physics Letters 99(25) 251908 (2011).
This PhD studentship is available for an immediate start. To discuss this project further contact:
Dr Maksym Myronov ([email protected]) and
Professor David R. Leadley ([email protected])