Heterojunction diodes comprised of n-type silicon and p-type ultrananocrystalline diamond/hydrogenated amorphous carbon composite

Heterojunction diodes comprised of p-type ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) and n-type Si, wherein 3 at.% boron-doped UNCD/a-C:H films were deposited on Si substrates by pulsed laser deposition, were electrically studied. The current-voltage (I-V) characteristics showed the typical rectification action with a leakage current density of 4.7 × 10^-5 A/cm² at a reverse voltage of -1 V. The carrier transport is expected to be in generation-recombination process accompanied by tunneling at low forward voltages of 0.1-0.5 V, and to be predominantly in tunneling at 0.5-1.0 V, from ideality factors estimated from the forward I-V curve. Grain boundaries in the UNCD/a-C:H film might act as centers for tunneling. From the capacitance-voltage measurement, the build-in potential of the heterojunction and an active carrier concentration in the p-type UNCD/a-C:H film were estimated to be 0.6 eV and 1.4 × 10 ¹⁷ cm^-3, respectively.