Structural and Electrical Characterization of Undoped Diamond Layer Grown by HF CVD

The undoped diamond layers were prepared using hot filament chemical vapor deposition technique. The controlled variation of the deposition parameters resulted in the layers with varying amount of nondiamond impurities. Routine characterization of the layers was carried out using scanning electron microscopy, X-ray diffractometry, and the Raman spectroscopy. Detailed measurements of room temperature electrical conductivity (σ₃₀₀), current-voltage characteristics have yielded useful information about the electrical conduction mechanism in this interesting material. The σ₃₀₀ and I-V characteristic measurements were done in sandwiched configuration taking care off the surface effects. The diamond shows room temperature dc conductivity reaching the values in the range of σ₃₀₀ ≈0.1-1 μS/cm. The I-V characteristics in these layers show space charge limited conduction behavior with I ~ V² in high voltage region. The obtained results are explained in terms of chemically adsorbed hydrogen on the surface of diamond layers, which is a source of acceptor states just above the top of valence band