The four-point probe technique is well known for its use in determining sheet resistance and resistivity (or effective resistivity) of thin films. Using a standard four-point probe setup, relatively large area samples are required. The convention is that the distance from any probe in the probe arrangement should be at least ten times the probe spacing from the sample boundary in order to use the fixed correction factor. In this paper we show, using computer modelling, how accurate measurements can be made using appropriate correction factors for samples that are either small or of any thickness. For the significant extent of variations used, the correction factor does not vary significantly.
Crystalline germanium substrates were amorphised to a depth of one micron by ion implantation of germanium ions at a series of relatively high energies and dose. Using the ion implantation modeling software TRIM, this paper compares the amorphisation results from the ion implantation simulations and experimental results from transmission electron microscopy (TEM) analysis of cross-sections of implanted samples. TEM cross-section micrographs show a clear boundary between amorphous and crystalline germanium. The effect of amorphisation of Ge on the subsequent formation of Nickel germanide is demonstrated and one significant issue is the increased depth of NiGe grains formed on a-Ge compared with c-Ge.
Nickel germanide is used as a contact material in germanium devices for making low resistance electrical contacts. It forms at relatively low temperatures compared to other germanides. Metal thickness, reaction temperature and duration of temperature are critical parameters. Here we report on the minimum temperature of formation of nickel germanide and on the effect of duration of temperature. Nickel germanide forms rapidly at higher temperatures and more slowly at lower temperatures and below a critical temperature it does not form, for any duration.
Low resistance contracts to highly doped silicon carbide (SiC) are investigated. Using a novel test structure that is easy to fabricate and easy to use, this paper demonstrates how it is used to reliably determine relatively low specific contact resistivities which vary with heat treatment. The test structure requires no error correction and is not affected by parasitic resistances. Using the test structure, small changes in specific contact resistivity are determined for small temperature changes. Results will be presented and discussed on the application of this novel test structure for nickel to highly doped SiC.
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