Yuuko Yokota

Cathodoluminescence and electroluminescence of undoped and boron‐doped diamond formed by plasma chemical vapor deposition

Visible luminescence between 2.0–3.5 eV of undoped and boron‐doped diamond formed by plasma‐assisted chemical vapor deposition has been investigated by cathodoluminescence. Electroluminescence from Schottky diode of boron‐doped semiconducting diamond has been observed for the first time and found to be due to the same luminescent center as that of cathodoluminescence. In the particles or films where the content of nitrogen and boron was greatly reduced, the cathodoluminescence peaks occurred at 2.8–2.9 eV. The characteristics of these emission spectra are very similar to those obtained in type‐IIa diamond where dislocations are luminescent. The doping of boron during the deposition form another luminescent center at 2.3–2.4 eV. From the monochromatic cathodoluminescence imaging, the luminescent regions differ in the two peaks. {100} sectors are much more luminescent than {111} sectors at the signal of 2.8 eV. This phenomenon has been discussed based on the difference in defect or impurity concentration of...

Field emission from phosphorus-doped polycrystalline diamond films

Field emission characteristics have been investigated for P-doped polycrystalline diamond films. It is demonstrated that the turn-on voltage of the electron emission decreases with increasing temperature for the P-doped diamond film, while no variation in the turn-on voltage occurs for the undoped diamond film. The temperature-dependent field emission characteristics are found to be inherent to the P-doped diamond film. A behavior of the field emission characteristics can be well explained by means of the thermionic field emission model combined with the temperature dependence of the ionized donor concentration. This means that an increase of the ionized donor concentration with increasing temperature may lead to a reduction in the tunnel barrier width at the interface between the diamond and the cathode, resulting in an enhancement of the internal emission current. It is suggested that the internal electron emission is important to the field emission characteristics of the P-doped diamond films. A variat...

Characteristics of metal-polycrystalline diamond contact field emitters

Abstract Electron emission characteristics have been investigated for polycrystalline diamond films. When the surface of the diamond films deposited on Si substrates and the rear face on which Au/diamond contact is formed are subjected to O 2 plasma treatment or annealing, an increase of the electric field commencing electron emission occurs in comparison with that for H 2 plasma-treated diamond surface. In the case of the surface treatment, emission characteristics are recovered by H 2 plasma treatment after O 2 plasma treatment or annealing, while no recovery of the electric field occurs for the Au/diamond sample in which the rear face of the diamond film is treated in the same manner. It is suggested that there exists another factor dominating the field emission characteristic other than field emission mechanisms such as electron injection at the diamond-metal contact and electron emission at the surface with negative electron affinity.

Electron emission characteristics of polycrystalline diamond films

Electron emission characteristics have been investigated for polycrystalline diamond films subjected to H2 plasma treatment, O2 plasma treatment, and annealing. In the case of surface treatments of diamond film, the voltage commencing electron emission increases due to O2 plasma treatment or annealing and is recovered by the subsequent H2 plasma treatment. On the other hand, in the case when the rear face of the diamond film is treated with O2 plasma or annealed in diamond/Au samples, no recovery of the voltage occurs due to H2 plasma treatment after O2 plasma treatment or annealing. It is suggested that there exists another factor dominating the field emission characteristic other than field emission mechanisms such as electron injection at the diamond/metal contact and electron emission at the surface with negative electron affinity.

Formation of optical centers in CVD diamond by electron and neutron irradiation

Abstract An investigation of the formation of optical centers in chemical vapor deposited diamond (CVD diamond) by electron and neutron irradiation has been carried out. Cathodoluminescence was mainly used for observation of the optical centers. Several optical centers have been observed after the irradiation and subsequent annealing at 900°C, such as the 5RL center and the centers with zero-phonon lines at 3.19 eV, 2.16 eV and 1.94 eV. Because these centers are considered to have relations to nitrogen atoms, vacancies or interstitials, it is expected that their luminescence intensities depend on the amount of nitrogen doping and radiation dose. However, decrease in the luminescence intensity with the amount of nitrogen doping has been observed. Boron-doped specimens have also been irradiated and annealed, but the formation of defects related to boron has not been observed.

Fabrication of boron nitride planar field emitters

Abstract Boron nitride (BN) films are grown on sapphire substrates by plasma-assisted chemical vapor deposition (PACVD). BN films are doped with sulfur. Insertion of the GaN layer between the BN film and sapphire leads to a tight adhesion of the BN film. The electrical resistivity of the sulfur-doped BN film is reduced to 10 3 Ω cm. The cathode electrode is formed on the BN film and the anode electrode on the sapphire substrate by evaporating Ti and Au. An emission current of 1 μA is obtained at an electric field strength of 16 V/μm.

Cathodoluminescence Of Vapour-Synthesized Diamond

Cathodoluminescence of diamond films has been investigated in the range of 2.0-3.5 eV. The CL spectra of diamond films are very sensitive to impurities such as nitrogen and boron. The main emission peak occurs around 2.8 eV in the films where the content of these impurities are lowered. The shape and behaviour of the spectra of the films are very similar to those obtained in natural type IIa diamond. The boron doping to the films increases the CL intensity. The luminescence is explained by donor-acceptor pair recombination where the acceptor is substitutional boron. In the semiconducting film, electroluminescence has been observed at metal/diamond(p-type) interfaces for the first time. From the CL imaging study, (100) growth sectors of diamond particle are much more luminescent than (111) sectors. This result indicates that the introduction of impurity or defect during crystal growth differs in each sectors.

Field Emission Characteristics from Grains and Polycrystalline Films of Phosphorus-Doped Diamond Grown by Chemical Vapor Deposition

Polycrystalline diamond films are prepared on Si substrates with various growth times by means of hot-filament chemical vapor deposition. Phosphorus atoms are doped as donor impurities. Field emission characteristics of diamond films are measured. Neither the film thickness nor the surface roughness has any influence on the field emission characteristics. The experimental results suggest internal electron emission from the Si substrate into the conduction band of the diamond. Moreover, it is found that the electron emission from diamond grains occurs at a lower electric field in comparison with that from diamond films.

Planar field emitters fabricated by sulfur-doped boron nitride

Fabrication of BN field emitters are tentatively attempted on sapphire substrates. In this paper, process technologies such as growth and etching of BN films are investigated. Electron emission is detected for a laterally fabricated field emitter.