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UBC Theses and Dissertations

Resistivity measurements of thin films of bismuth : applications for building bolometric detectors Padwick, Christopher Grant


The resistivity of thin bismuth films grown on sapphire substrates has been measured as a function of growth rate, thickness, and temperature. Seven different samples were measured. In all cases the resistivity of the films was completely unlike the resistivity of the bulk material, and each sample exhibited a negative temperature coefficient of resistance (TCR). A model is presented which provides a physical interpretation of the shape of the resistivity - temperature curve of thin bismuth films. This model is a new contribution to this field of research, since there appears to be no satisfactory explanation for the anomalous temperature dependence of the resistivity of thin bismuth films published in the literature. The sheet resistance of the films at 4.2K was found to decrease with increasing thickness. Based on the experimental data, a bismuth film of thickness 200Å should have a sheet resistance of 188.5Ω/ at helium temperatures. The resistance of the thinner films was found to increase as a function of time when exposed to the air, and this seems to be consistent with a layer of insulating Bi₂O₃, forming at the surface of the film. The sheet resistance and resistivity of a 5000Å thick coating of vapor deposited aluminum was measured as a function of temperature in the range 300K — 4.2K. The resistivity was found to be greater than that of the bulk material at all temperatures, and the sheet resistance at 80K was equal to R = 0.051Ω.

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