Hideto Miyake

Fabrication of Deep-Ultraviolet-Light-Source Tube Using Si-Doped AlGaN

An ultraviolet (UV)-light-source tube using a Si-doped AlGaN film as a target of electron beam excitation was fabricated. The Si-doped AlGaN was grown on an AlN/sapphire substrate by low-pressure metalorganic vapor phase epitaxy (LP-MOVPE), and its optical properties were evaluated by excitation with a 10 kV electron beam (EB). Emission intensity was significantly improved by Si doping and optimization of the growth conditions. 247 nm deep-UV light was observed from the tube, and the lifetime of the light tube until 50% emission output of the initial strength was approximately 2000 h at an EB acceleration voltage of 10 kV with a current of 100 µA.

Impacts of Si-doping and resultant cation vacancy formation on the luminescence dynamics for the near-band-edge emission of Al0.6Ga0.4N films grown on AlN templates by metalorganic vapor phase epitaxy

Luminescence dynamics for the near-band-edge (NBE) emission peak at around 250u2009nm of c-plane Si-doped Al0.6Ga0.4N films grown on AlN templates by low-pressure metalorganic vapor phase epitaxy were studied using deep ultraviolet time-resolved photoluminescence and time-resolved cathodoluminescence spectroscopies. For the films with the Si-doping concentration, [Si], lower than 1.9u2009×u20091017u2009cm–3, the doping lessened the concentration of cation vacancies, [VIII], through the surfactant effect or the aid of the reactant doping in a form of H3SiNH2. However, the room-temperature nonradiative lifetime, and, consequently, the equivalent value of internal quantum efficiency in the weak excitation regime steeply decreased when [Si] exceeded 1018u2009cm−3. Simultaneously, the intensity ratio of the deep-state emission band to the NBE emission abruptly increased. Because the increase in [Si] essentially gives rise to the increase in [VIII] (for [Si]>1.9×1017u2009cm−3) and the overcompensation of Si is eventually observed for ...

Microstructure of AlN grown on a nucleation layer on a sapphire substrate

The growth conditions and interface microstructure of AlN on sapphire grown using a nucleation layer (NL) have been studied. The AlN layer with NL-AlN grown at 1100 °C exhibits a smooth surface morphology. The epilayer has a small amount of tilting but the twisting is large. For the AlN layer with NL-AlN grown at 1250 °C, the twisting is reduced, but the surface is rough owing to the mixing of crystallographic polarity. The origins of AlN inversion domains are discussed by considering the microstructures observed by transmission electron microscopy (TEM), with the ultimate aim of growing a high-quality AlN layer.

Growth of Thick AlN Layer by Hydride Vapor Phase Epitaxy

Thick AlN crystals were grown by conventional hydride vapor phase epitaxy (HVPE) on AlN/sapphire templates under low pressure (~15 Torr) at high temperature (1100°C–1200°C). Colorless, mirror-like AlN films were obtained at the growth rates of up to 20.6 µm/h. The best root mean square (RMS) value of atomic force microscope (AFM) observations for the AlN surface was 2.34 nm. The typical values of full width half maximum (FWHM) of X-ray rocking curves for (0002) and (1012) diffraction of AlN films were 173–314 arcsec and 1574–1905 arcsec, respectively. We also investigated the influences of carrier gas, growth temperature and growth rate on the crystal quality.

Raman Scattering Spectroscopy of Residual Stresses in Epitaxial AlN Films

High-crystalline-quality epitaxial films of wurtzite AlN were grown by metalorganic vapor phase epitaxy (MOVPE) and hydride vapor phase epitaxy (HVPE). The lattice strain of the films was analyzed by high-resolution X-ray diffraction and the E2 (high)-phonon frequency was observed by Raman scattering. Data analysis for wide ranges of lattice strains and phonon-peak shifts yielded a precise biaxial stress coefficient of this phonon mode, -4.04±0.3 cm-1/GPa. Furthermore, the deformation potential constant was accurately determined from the biaxial stress coefficient.

Effects of Substrate Plane on the Growth of High Quality AlN by Hydride Vapor Phase Epitaxy

We investigated the direct growth of c-plane AlN on sapphire (11.0) and (00.1) substrates by low-pressure hydride vapor phase epitaxy (LP-HVPE) without using any buffer, interlayer, or pulsed source supply. The a-plane sapphire was confirmed to be effective for obtaining high-quality AlN with an rms surface roughness of 0.156 nm for 2×2 µm2 scan and a large crack-free thickness of 3.6 µm. This was partly attributed to the hexagonal c-axis of a-sapphire substrate being perpendicular to the hexagonal c-axis of AlN, leading to the reduced twist degree of AlN. X-ray rocking curves yielded full widths at half maximum (FWHM) of 487 and 636 arcsec for (10.2) and (10.0) reflections, respectively, indicating a low edge dislocation density (reduced twist degree) in the film.

Fabrication of carbon nanotube array and its field emission property

In this paper, we employed the PE-CVD and a lift-off process using silicon substrates. Field emission from the CNT array, which was fabricated by means of this technique, was investigated.

Nitridating r-plane sapphire to improve crystal qualities and surface morphologies of a-plane GaN grown by metalorganic vapor phase epitaxy

Effects of the nitridation of the r-plane sapphire were investigated on the growth of a-plane GaN. Surface morphology and crystal quality were very sensitive to the nitridated time. A high quality a-plane GaN with a pit free-surface was obtained with nitridation at 1100u2009°C for 5 min, compared with under- or overnitridation. Nitridated layer were identified as AlN grains with ⟨112¯0⟩ preferred orientation, which acted as the nuclearation layers for a-plane GaN growth. Moreover, the qualities improvements were attributed to enhancing grain uniformity and size with 5 min nitridation.

Effect of strain on quantum efficiency of InAlN-based solar-blind photodiodes

A series of InxAl1−xN-based Schottky solar-blind photodiodes are fabricated on the InxAl1−xN epilayers with high and very close crystal qualities. The quantum efficiency varies from 14.5% to 68.5%. The microstructure and strain state of epilayers are investigated in detail. It is found that the quantum efficiency of photodiode depends on the strain state in InxAl1−xN films. This indicates that adjusting the strain state in InxAl1−xN film is one of the promising approaches to optimize the performance of InAlN-based solar-blind photodiode.

Growth and Characterization of AlGaN Multiple Quantum Wells for Electron-Beam Target for Deep-Ultraviolet Light Sources

The structure of Si-doped AlGaN multiple quantum well (MQW) targets has been optimized for application to electron-beam (EB)-pumped deep-ultraviolet (UV) light sources. The deep-UV light emission from Si-doped AlGaN MQW targets pumped by a 10 kV EB has been evaluated. The targets exhibited a deep-UV light output power of over 15 mW at a peak wavelength of 256 nm for an EB input power of 2.0 W, and the conversion efficiency was estimated to be over 0.75%. These results demonstrate the advantageousness of using p-type-AlGaN-free AlGaN MQW targets as a material for application to EB-pumped deep-UV light sources.