Sausan Al-Riyami

Nitrogen-Doped Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films Prepared by Pulsed Laser Deposition

Nitrogen-doped ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films were deposited by pulsed laser deposition. The film doped with a nitrogen content of 7.9 at. % possessed n-type conduction with an electrical conductivity of 18 Ω-1cm-1 at 300 K. A heterojunction with p-type Si exhibited typical rectifying action. The UNCD grain size was estimated to be 2.5 nm from X-ray diffraction measurement. Near-edge X-ray absorption fine-structure and Fourier transform infrared spectroscopies revealed the preferential formations of C=N and C–N bonds and an enhanced amount of sp2 bonds in the films.

Near-edge X-ray absorption fine structure of ultrananocrystalline diamond/hydrogenated amorphous carbon films prepared by pulsed laser deposition

The atomic bonding configuration of ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C:H) films prepared by pulsed laser ablation of graphite in a hydrogen atmosphere was examined by near-edge X-ray absorption fine structure spectroscopy. The measured spectra were decomposed with simple component spectra, and they were analyzed in detail. As compared to the a-C:H films deposited at room substrate-temperature, the UNCD/a-C:H and nonhydrogenated amorphous carbon (a-C) films deposited at a substrate-temperature of 550°C exhibited enhanced π* and σ*C≡C peaks. At the elevated substrate-temperature, the π* and σ*C≡C bonds formation is enhanced while the σ*C-H and σ*C-C bonds formation is suppressed. The UNCD/a-C:H film showed a larger σ*C-C peak than the a-C film deposited at the same elevated substratete-temperature in vacuum. We believe that the intense σ*C-C peak is evidently responsible for UNCD crystallites existence in the film.

Heterojunction Diodes Comprising p-Type Ultrananocrystalline Diamond Films Prepared by Coaxial Arc Plasma Deposition and n-Type Silicon Substrates

Heterojunction diodes, which comprise boron-doped p-type ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films prepared by coaxial arc plasma deposition and n-type Si substrates, were electrically studied. The current–voltage characteristics showed a typical rectification action. An ideality factor of 3.7 in the forward-current implies that carrier transport is accompanied by some processes such as tunneling in addition to the generation–recombination process. From the capacitance–voltage measurements, the built-in potential was estimated to be approximately 0.6 eV, which is in agreement with that in a band diagram prepared on the assumption that carriers are transported in an a-C:H matrix in UNCD/a-C:H. Photodetection for 254 nm monochromatic light, which is predominantly attributable to photocurrents generated in UNCD grains, was evidently confirmed in heterojunctions. Since dangling bonds are detectable by electron spin resonance spectroscopy, their control might be an important key for improving the rectifying action and photodetection performance.

Carrier transport and photodetection in heterojunction photodiodes comprising n-type silicon and p-type ultrananocrystalline diamond/hydrogenated amorphous carbon composite films

Carrier transport and photodetection in heterojunction photodiodes comprising n-type Si substrates and p-type B-doped ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films were investigated. Their transport model was discussed mainly on the basis of electrical measurements. It was revealed that an a-C:H matrix in UNCD/a-C:H would predominantly be responsible for carrier transportation in the photodiodes. The photodiodes exhibited high external quantum efficiencies of 72 and 23% under 254 and 365 nm UV illuminations, respectively. These superior responses might be attributable to the photocarrier generation in UNCD grains accompanied by an efficient carrier transport to the a-C:H matrix.

Near-Edge X-ray Absorption Fine-Structure Spectroscopic Study on Nitrogen-Doped Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films Prepared by Pulsed Laser Deposition

Nitrogen-doped ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C:H) composite films, which possessed n-type conduction with enhanced electrical conductivity, were prepared by pulsed laser deposition. The film doped with a nitrogen content of 7.9 at. % possessed enhanced electrical conductivity of 18 Ω-1cm-1 at 300 K. The near-edge X-ray absorption fine-structure (NEXAFS) measurement indicated the appearance of additional peaks due to π* C=N, σ* C=N, and σ* C–N bonds compared with the spectra of undoped films. The sp2 bonding fraction estimated from the NEXAFS spectra increased with the nitrogen content. The enhanced electrical conductivity is probably due to the formation of additional π* and σ* states and the enhancement in the sp2 bonding fraction.

Effects of Hydrogen and Nitrogen Atmospheres on Growth of Ultrananocrystalline Diamond/Amorphous Carbon Composite Films by Reactive Pulsed Laser Deposition

The growth of ultrananocrystalline diamond/nonhydrogenated amorphous carbon composite films was realized by pulsed laser deposition with a graphite target in a nitrogen atmosphere totally excluding hydrogen. The existence of 7 nm diamond grains was confirmed by X-ray diffraction. Nitrogen incorporation into the films was confirmed by X-ray photoemission and near-edge X-ray absorption structure spectroscopies, and the nitrogenation produced n-type conduction with an electrical conductivity of 0.2 Ω-1 cm-1 at 300 K. The results of study proved that nitrogen acts as a reactive gas for the formation of diamond grains, similarly to hydrogen.

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 ×1017 cm-3, respectively.