University of Twente Student Theses


Growth and characterisation of thin film Mott insulator p-n junctions

Bruijnes, F. and Smink, A.E.M. (2012) Growth and characterisation of thin film Mott insulator p-n junctions.

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Abstract:In this report of a BSc assignment, investigations of properties of the materials LSCO (x=0.09) and NCCO (x=0.10) grown on an LSAT substrate with an STO capping are described. In particular, the electrical properties of these materials in p-n junctions and in an alternating multilayer are characterised. The growth of a new multilayer sample of Mott insulators LSCO and NCCO is described and analysed. Techniques to grow thin films are introduced and discussed. For the growth pulsed laser deposition, photolithography, sputtering and Argon etching have been used. The sample quality has been determined using atomic force microscopy, x-ray diffraction and reflectivity and resistance measurements. This quality is concluded to be fair, certainly for a first ever attempt to grow such a sample. The theory to analyse the results is presented, which includes Mott insulator physics, p-n junction theory, thin film characterisation, theory on superconductivity and antiferromagnetism. A parallel is made between semiconductor p-n junctions and superconducting p-n junctions. The measurement methods, which include four-point measurements, lock-in measurements and IVT-measurements are discussed. The results are presented as IV-curves, IVT-diagrams and dV/dI curves to provide insight into p-n behaviour, transitions in the phase diagram and possible new effects arising from the properties of the sample. The measurements done provided a large amount of information. For the single layer sample, p-n behaviour has been confirmed and material property transitions have been seen in the IVT-diagrams. Semiconductor-like pnp behaviour is confirmed as well, and the low bias resistance appears to be dominated by the first junction in the current path. The multilayer sample displayed a wide variety of measurement results, despite only four junctions having been measured. Both ohmic and non-linear IV-curves have been observed at 300 K and superconductivity emerges in the LSCO at about 15-20 K. Indications for phase transitions have also been measured and provide clues for further research.
Item Type:Essay (Bachelor)
Faculty:TNW: Science and Technology
Subject:53 electrotechnology
Programme:Applied Physics BSc (56962)
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