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Title: Optimisation of superconducting thin film growth for next generation superconducting detector applications
Author: Banerjee, Archan
ISNI:       0000 0004 6421 8658
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 2017
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There is a growing demand for superconducting detectors with single photon sensitivity from near- to far infrared wavelengths. Emerging application areas include imaging, remote sensing, astronomy and free space communications. Two superconducting device technologies, superconducting nanowire single-photon detectors (SSPDs/SNSPDs) and microwave kinetic inductance detectors (MKIDs) have the potential to outperform off-the-self semiconductor technologies and offer scalability to large arrays. Fabrication of high efficiency superconducting detectors strongly depends on the quality of superconducting thin films. The original work presented in this thesis has explored the growth and optimization of several superconducting thin film materials for next generation superconducting detectors. Films have been grown in an ultra-high vacuum sputter deposition system and an atomic layer deposition system. Since its initial demonstration, NbN and NbTiN have been predominantly used as the base material for SNSPDs. In this work, we have explored the optimization of both the materials with an emphasis on NbTiN. NbTiN is optimized by heating the substrates to 800 ̊C achieving a Tc of 10.4 K for a film thickness of 5.5 nm on silicon substrate. Due to their crystalline nature superconducting properties of NbN or NbTiN thin films are strongly correlated with the lattice parameters of substrate properties. This causes a restriction on the substrate choice and integration of SNSPD devices with complex circuits. Amorphous superconducting materials can be promising alternatives for this purpose. We have explored growth and optimization of amorphous MoSi and MoGe thin films. Both the materials are co-sputtered to tune the composition. For 5 nm thick MoSi film on silicon substrate we obtain Tc of 5.5 K. For MKID fabrication, TiN can be an useful base material due to its high sheet resistance and widely tuneable superconducting properties. TiN thin films have been sputtered on heated (500 ̊C) silicon substrates with a Tc of 3.9 K for a 90 nm thick film. The dielectric constants of the thin films as a function of wavelength (270-2200 nm) have been determined via variable angle spectroscopic ellipsometry (VASE). Atomic structure and stoichiometry of the films have been characterized in high resolution transmission electron microscopy (HRTEM). This study enables us to precisely control film properties and thus tailor superconducting films to the requirements of specific photon-counting applications.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics ; TK Electrical engineering. Electronics Nuclear engineering