Electrical Properties of Doped and Undoped Homoepitaxial Diamond Layers Grown by Microwave Plasma CVD

The electrical properties of homoepitaxial diamond layers have been investigated by I-V, C-V and frequency-dependent capacitance measurements. Undoped and B-doped diamond layers were grown by microwave plasma CVD on Ib (100) diamond substrates. Lateral Schottky barrier diodes were fabricated on these diamond layers. Individual Schottky contact (Au/Ni dot electrode) was surrounded by the ohmic contact (Au/Pt/Ti) with 20 micron gap. The contact pads have three kinds of area, which were 7.5 x 10-4 square centimeters, 3.4 x 10-4 square centimeters and 2.0 x 10-4 square centimeters, respectively. The ohmic contact area was greater than 150 times that of the largest dot. B, N, H, and O concentrations were determined by SIMS measurements. The ideality factor n and barrier height for the Schottky junctions were typically found to be in 1.2 to approximately 1.3 and to be approximately 1.1eV, respectively, from the results of I-V measurements. The results of frequency-dependent capacitance measurements, with a frequency ranging from 10 Hz to 1 MHz, have shown the well-known dispersion effect, which occurs when a deep level is unable to follow the high-frequency voltage modulation and contribute to the net space charge in the depletion region. Net acceptor concentrations in the B-doped diamond layers were found to be 1-6 x 1017 per cubic centimeter. The correlation between net acceptor concentration and B concentration was revealed.