Nonuniform conduction in B-doped chemical vapor deposited diamond studied by intra- and intergrain measurements

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Abstract
Current–voltage (I–V) measurements are performed on a B-doped polycrystalline diamond film chemically vapor deposited on commercially available 170-μm-thick undoped and polished polycrystalline diamond. Four-probe resistivity measurements in the temperature range of 7–200 °C, potential profile measurements across a few grains in the current range of 10−6–10−4 A, and two-probe I–V measurements within a single grain and across an individual grain boundary show that: (i) current flow is nonuniform and is affected by current level, (ii) potential barriers exist at the grain boundaries, and (iii) the probe contacts are Ohmic when the probes are placed on rough microstructures. Based on the grain size distribution, a simple model that distinguishes between conduction paths made of large grains and small grains is used to interpret these results.