Amirhaghi, Sasson; (1994) Pulsed laser deposition of electronic materials. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The technique of pulsed laser deposition (PLD) which has been studied since the development of high power lasers, offers numerous advantages over other thin film techniques which include, film stoichiometry close to that of the source target material, low contamination levels, high deposition rate and dissociative evaporation. This project involves the use of PLD to grow thin films of oxide materials and investigate the deposition parameters involved. During the course of the project characterization techniques such as x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and low temperature resistance measurements were utilized. High temperature superconductor oxides (HTSC) based on copper and rare alkaline earths are chemically and structurally complex materials in which the preservation of stoichiometry is essential. Thus PLD is an attractive deposition method for producing such materials in thin film form. In order to grow HTSC films on commercially desirable substrates such as silicon, an inter-mediate buffer layer is required to avoid the detrimental problems of chemical interaction and/or interdiffusion during high temperature annealing processes. The in-situ growth of high quality CeO2 thin films used as buffer layers is highly dependent on the deposition conditions. In this project a number of parameters such as substrate temperature, oxygen partial pressure, film thickness, choice of laser (wavelength) and the target surface are investigated. Single crystal wafers of Si(100) and Si(111) together with sapphire and Corning glass 7059 were used as substrates. The possibility of growing multilayers with a gradual change in lattice constant to ensure better lattice matching to the top layer(s) is shown by depositing a film of CeO2 doped with La over an undoped CeO2 film. The growth of cuprates such as YBa2Cu3O7-δ on Si with CeO2 as a buffer layer is also shown. The preparation of the electron doped cuprate, Nd2-xCexCuO4-y, (0.13<x<0.18 and y=0.04), in bulk and thin film form is studied. A number of parameters involved in producing highly textured single phase thin films of this material by in-situ and ex-situ growth on MgO single crystal substrates are examined. The effect of varying the Ce concentration on crystal dimensions of the bulk material is also investigated. Thin films of ZnO are widely used in electronic device technology as optically transparent materials exhibiting large piezoelectric and piezooptic effects when highly textured. In this project a number of parameters involved in growing ZnO films on Si and Corning glass 7059 are examined.

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