Tomohide Yamamoto

Electron field emission from boron-nitride nanofilms

Hexagonal polycrystalline boron-nitride (BN) films are synthesized on Si substrates by plasma-assisted chemical-vapor deposition. In the case of BN films thicker than 20 nm, the turn-on electric field of the electron emission decreases with increasing surface roughness. On the other hand, in the case of BN film as thin as 8–10 nm, it is found that the turn-on electric field is reduced to 8.3 V/μm in spite of the surface of the BN nanofilm being flat, as well as the Si substrate. The Fowler–Nordheim (FN) plot of the field-emission characteristics of the BN nanofilm indicates a straight line, suggesting the presence of FN tunneling. This finding means that introduction of the BN nanofilm leads to a significant reduction in the effective potential barrier height.

Field emission from GaN surfaces roughened by hydrogen plasma treatment

GaN layers are grown on sapphire substrates with AlN buffer layers by the metalorganic chemical vapor deposition method. GaN layers are doped with Si. The electron density of the n-type GaN is 2×1017 cm−3. It is found that the GaN surface is etched with hydrogen (H2) plasma produced by supplying microwave power leading to the formation of the roughened surface of GaN. A variation in the surface morphology occurs due to microwave power and gas pressure. Field emission measurements are carried out for GaN with various surface morphologies. It is observed that the turn-on electric field decreases with increasing surface roughness of the GaN. A turn-on electric field of the electron emission is estimated to be as low as 12.4 V/μm.

Study on electrical characteristics of metal/boron nitride/metal and boron nitride/silicon structures

Abstract Polycrystalline boron nitride films are synthesized by plasma-assisted chemical vapor deposition (PA-CVD). Metal/BN/metal samples are fabricated and electrical characterization are performed for metal (Ni,Cu,Ti)/BN contacts. Ni/BN contact can be regarded as an ohmic property. However, Cu/BN and Ti/BN contacts show Schottky characteristics. For the Ti/BN sample, Schottky barrier height as high as 1 eV is achieved. It is found that the BN films show p-type conduction from the relationship between Schottky barrier height and metal work function. Also fabricated is a Ni/BN/n–Si diode, current–voltage ( I – V ) characteristics of which demonstrate a rectification ratio as high as 10 5 .

Field emission characteristics of BN/GaN structure

n-type gallium nitride (GaN) layers grown on sapphire substrates by metalorganic chemical vapor deposition are used to examine field emission characteristics. The electron concentration of the GaN is 2×1017 cm−3. In order to enhance the electric field, the GaN surface is roughened by hydrogen (H2) plasma treatment. Boron nitride (BN) films are grown on the roughened surface of the GaN by plasma-assisted chemical vapor deposition. The turn-on electric field between the anode and sample surface is estimated to be 12.4 and 8.8 V/μm from the field emission characteristics of the roughened GaN and the BN/GaN samples, respectively. It is demonstrated that BN coating is effective in improving the field emission characteristics.

Field emission characteristics of carbon nanofiber improved by deposition of boron nitride nanocrystalline film

An improvement in field emission characteristics of a graphite nanofiber (GNF) has been attempted. Boron nitride (BN) films are synthesized by plasma-assisted chemical vapor deposition. It is demonstrated that electron emission occurs at a low anode voltage due to depositing the BN nanocrystalline film on flat Si substrates. Deposition of the BN nanocrystalline film is applied to the GNF to improve the field emission characteristics of the GNF. In addition to a reduction in the average turn-on electric field, the emission current increases by two orders of magnitude in comparison with that of an as-grown GNF.

Field emission characteristics of boron nitride films deposited on Si substrates with cubic boron nitride crystal grains

Field emission characteristics are investigated for boron nitride (BN) films deposited on Si substrates with cubic (c-)BN crystal grains. A comparative study of field emission characteristics is performed for the BN samples with and without c-BN grains. The turn-on electric fields are 7 and 18 V/μm for the BN samples with and without c-BN grains, respectively. A significant reduction in the turn-on electric field of the electron emission is found for the sample with c-BN grains. Fowler–Nordheim plots of the field emission characteristics suggest a variation in the field enhancement factor between the BN samples with and without c-BN crystal grains. It is also found that c-BN crystal grains are effective in increasing electron emission area.

Tunneling controlled field emission of boron nitride nanofilm

Abstract Hexagonal polycrystalline boron nitride (BN) films are synthesized on Si substrates by plasma assisted chemical vapor deposition. In the case of the BN films thicker than 20 nm, the turn-on electric field of the electron emission decreases with increasing surface roughness. It is suggested that electron emission occurs due to Fowler–Nordheim tunneling through the surface potential barrier. An introduction of the BN nanofilm is proposed to reduce the operation electric field of the electron emission. The turn-on electric field of 8.3 V/μm is achieved for the BN nanofilm with a thickness of 8–10 nm, the surface roughness of which is almost the same as that of the flat Si substrate. It is demonstrated that an introduction of the BN nanofilm is effective in improving the field emission characteristics.

Electron field emission from boron nitride nanofilm and its application to graphite nanofiber

Hexagonal polycrystalline boron nitride (BN) films are synthesized on Si substrates by plasma assisted chemical vapor deposition. In the case of the BN films thicker than 20 nm, the turn-on electric field of the electron emission is strongly influenced by the surface roughness rather than the film thickness. On the other hand, in the case of the BN film with a thickness of 8–10 nm, it is found that the turn-on electric field as low as 8.3 V/μm is achieved in spite of the surface of the BN nanofilm being flat as well as the Si substrate. A significant reduction in the effective potential barrier height is suggested. The tunneling controlled field emission is proposed for the BN nanofilm with positive space charge. The BN nanofilm is deposited onto the graphite nanofiber sample. A significant improvement of the field emission characteristics is demonstrated.

Formation of Rough GaN Surface by Hydrogen Plasma Treatment and Its Application to Field Emitter

N-type GaN layers doped with Si are grown on sapphire substrates with AlN buffer layers by the metalorganic chemical vapor deposition method. The electron density is 2×1017 cm-3. The GaN surface is treated with hydrogen (H2) plasma produced by supplying microwave power. Etching of GaN with H2 plasma leads to the formation of a roughened GaN surface. An enhancement of the electric field at the roughened surface makes it possible to reduce the average electric field between the anode electrode and the sample surface for electron emission. The turn-on electric field for the electron emission is estimated to be as low as 12.4 V/µm.

Improved field-emission characteristics of GaN by BN coating

Using coating with a boron nitride (BN) film, we attempted to improve field-emission characteristics of gallium nitride (GaN) cold cathodes. First, we measured the field-emission characteristics of BN/n-Si samples to investigate the electron-emission mechanism of the BN film. We discuss the electron-emission process of the BN film in terms of the surface roughness dependence of the field-emission characteristics. We suggest that the coating with a BN film thinner than 10 nm is effective in reducing the turn-on voltage of the electron emission. Second, field-emission characteristics are examined for the hexagonal n-type GaN layers roughened with H2 plasma treatment. Moreover, nanocoating with a BN film is carried out on the surface of the GaN sample for the BN/GaN sample. We achieved a turn-on electric field as low as 4.6 V/μm.