H. Amano

Nagoya University | Meidai · Department of Electrical Engineering and Computer Science

A non-filter virus inactivation unit was developed that can control the irradiation dose of aerosolized viruses by controlling the lighting pattern of a 280 nm deep-UV (DUV)-LED and the air flowrate. In this study, the inactivation properties of aerosolized SARS-CoV-2 were quantitatively evaluated by controlling the irradiation dose to the virus in...

Photocathodes with negative electron affinity (NEA) characteristics have various advantages, such as small energy spread, high spin polarization, and ultrashort pulsing. Nitride semiconductors, such as GaN and InGaN, are promising materials for NEA photocathodes because their lifetimes are longer than those of other materials. In order to further p...

A general-purpose virus inactivation unit that can inactivate viruses was developed using deep ultraviolet (DUV) LEDs that emit DUV rays with a wavelength of 280 nm. The inside of the virus inactivation unit is a rectangular conduit with a sharp turn of 180 (sharp-turned rectangular conduit). Virus inactivation is attempted by directly irradiating...

A desktop-type air curtain system (DACS) capable of being installed on a desk to protect healthcare workers from infectious diseases was developed. Pseudo-exhaled air containing aerosol particles emitted from a mannequin was blown toward the air curtain generated by the DACS. The aerosol blocking effect of the DACS was investigated using particle i...

A virus inactivation unit that can inactivate viruses was developed using deep ultraviolet (DUV) LEDs that emit DUV rays with a wavelength of 280 nm. The flow characteristics of virus particles inside the virus inactivation unit were investigated using numerical simulations. The percentage of particles colliding on the inner wall of the virus inact...

A desktop-type air curtain device capable of being installed on a desk to protect healthcare workers from infectious diseases was developed. Pseudo-exhaled air containing aerosol particles emitted from a mannequin was blown toward the air curtain generated by the air curtain device. The aerosol blocking effect of the air curtain device was investig...

A challenging approach, but one providing a key solution to material growth, remote epitaxy (RE)-a novel concept related to van der Waals epitaxy (vdWE)-requires the stability of a two-dimensional (2-D) material. However, when graphene, a representative 2-D material, is present on substrates that have a nitrogen atom, graphene loss occurs. Although...

The leakage current caused by the Si pileup at the regrowth interface of AlGaN/GaN high electron mobility transistors (HEMTs) is significantly suppressed by the semi-insulating Mg-doped GaN layer. Mg is unintentionally doped and can be originated from the graphite susceptor of metal organic vapor phase epitaxy. Before regrowth of the AlGaN/GaN hete...

Core–shell nanorods (NRs) with InGaN/GaN quantum wells (QWs) are promising for monolithic white light-emitting diodes and multi-color displays. Such applications, however, are still a challenge because intensity of the red band is too weak compared with blue and green. To clarify this problem, we measured photoluminescence of different NRs, dependi...

In this work, we analyze and model the effect of a constant current stress on an ultraviolet light-emitting diode with a nominal wavelength of 285 nm. By carrying out electrical, optical, spectral, and steady-state photocapacitance (SSPC) analysis during stress, we demonstrate the presence of two different degradation mechanisms. The first one occu...

Recent experiments suggest that Mg condensation at threading dislocations induces current leakage, leading to degradation of GaN-based power devices. To investigate this, we perform first-principles total-energy electronic-structure calculations for various Mg and dislocation complexes. We find that threading screw dislocations (TSDs) indeed attrac...

Core-shell nanorods (NRs) with InGaN/GaN quantum wells (QWs) are promising for monolithic white light-emitting diodes and multicolor displays. Such applications, however, are still a challenge because intensity of red band is too weak as compared with blue and green ones. To clarify the problem, we have performed power and temperature dependent, as...

Within this paper, we present an extensive analysis of the degradation of UV-B light-emitting diodes (LEDs) submitted to constant current stress. The study is based on combined electrical, optical and spectral characterization, and capacitance deep-level transient spectroscopy (C-DLTS). The results of this analysis demonstrate that the decrease in...

InGaN quantum wells were grown using metalorganic chemical vapor phase epitaxy (vertical and horizontal types of reactors) on stripes made on GaN substrate. The stripe width was 5, 10, 20, 50, and 100 µm and their height was 4 and 1 µm. InGaN wells grown on stripes made in the direction perpendicular to the off-cut had a rough morphology and, there...

Precise Measurement of Carrier Concentrations in n-Type GaN by Phase-Shifting Electron Holography - Volume 25 Supplement - Kazuo Yamamoto, Kiyotaka Nakano, Atsushi Tanaka, Yoshio Honda, Yuto Ando, Masaya Ogura, Miko Matsumoto, Satoshi Anada, Yukari Ishikawa, Hiroshi Amano, Tsukasa Hirayama

Graphene has been adopted in III−V material growth since it can reduce the threading dislocations and the III−V epilayer can easily be separated from the substrate due to the weak chemical bond. However, depending on the substrate supporting the graphene, some substrates decompose in the III−V material growth environment, which results in the probl...

Mg diffusion is a common problem in GaN devices with p–n junctions. Although this impurity diffusion is reported to occur through threading dislocations (TDs), no direct evidence has yet been obtained. Therefore, we tried the direct observation of Mg diffusion by atom probe tomography (APT) analysis. The n-type drift layer of the fabricated p–n dio...

This study investigated the change in carrier concentration near the surface of a silicon substrate during gallium nitride (GaN) growth with an aluminum nitride (AlN) buffer layer. It was observed that aluminum, gallium, and carbon diffused into the silicon substrate during the growth process and that the carrier concentration increased with increa...

We report on the growth, processing and optical characterization of monolithically integrated tricolor micro-LEDs. The 100 × 100 μ m ² active area of the devices is composed of independent subpixels emitting in the blue, green and yellow–orange range with color saturation of over 90% for all bands. The gamut of the device is recorded by both digita...

We fabricated p−n diodes under different growth pressures on free-standing GaN substrates of the same quality and observed a noteworthy difference in the reverse leakage current. A large reverse leakage current was generated by nanopipes, which were formed from screw dislocations in the homoepitaxial layer. There were two types of screw dislocation...

Recessed-gate AlGaN/GaN metal–insulator–semiconductor (MIS) high electron mobility transistors (HEMTs) were fabricated by utilizing a photoelectrochemical (PEC) etching and a post-metallization annealing (PMA) process. In order to demonstrate the device performance and reliability, both electrical and optical electroluminescence (EL) properties wer...

AlGaN multiple quantum wells (MQWs) targeting 265 and 285 nm deep-ultraviolet LEDs grown on AlN templates with macrosteps were compared. In the cathodoluminescence images of the 285 nm MQW, high-intensity zones were observed along the edgelines of the macrosteps with wavelengths of 290–296 nm and on the terraces with wavelengths of 286–288 nm. Dark...

In order to advance the mass production of graphene devices, it is beneficial to avoid the difficulty graphene transfer process. Direct precipitation of graphene using a tungsten capping layer is convenient for this purpose, and is quite simple and compatible with conventional semiconductor fabrication processes. In this study, multilayer graphene...

Vertical Schottky barrier diodes (SBD) with different drift-layer thicknesses (DLT) of GaN up to 30 μm grown by metalorganic chemical vapour deposition (MOCVD) were fabricated on free-standing GaN grown by hydride vapour phase epitaxy (HVPE). At room temperature, SBD’s exhibited average barrier heights (ΦB) in the range of 0.73 eV to 0.81 eV. The e...

Individual core–shell GaN nanorods (NRs) with InGaN quantum wells (QWs), lying in non‐polar, semi‐polar, and polar planes, are investigated by micro‐photoluminescence (μ‐PL) spectroscopy. Complementary transmission electron microscopy (TEM) studies reveal the presence of basal stacking faults (BSFs), which intersect the QWs. Narrow peaks of exciton...

The decomposition of ammonia (NH 3 ) in nitrogen (N 2 ) ambient was studied under non-equilibrium conditions similar to those in a metal organic vapor phase epitaxy (MOVPE) reactor during the epitaxial growth of group-III nitrides. The gas phase was sampled at different positions and analyzed using a time-of-flight mass spectrometry system with a h...

Effect of drift layer thicknesses (DLT) (2, 15 and 30 μm) in reverse current conduction mechanisms of vertical GaN-on-GaN Schottky Barrier Diodes grown MOCVD has been investigated for the first time. The conduction mechanism is changing from thermionic field emission (TFE) to thermionic emission (TE) when the DLT of GaN increases. The SBDs with DLT...

A normally-off GaN double-implanted vertical MOSFET (DMOSFET) with an atomic layer deposition (ALD)-Al2O3 gate dielectric film on a free-standing GaN substrate fabricated by triple ion implantation is presented. The DMOSFET was formed with Si ion implanted source regions in a Mg ion implanted p-type base with N ion implanted termination regions. A...

We demonstrate the fabrication of 100 x 100 um^2 nitride-based tricolor micro-LEDs. While the optical properties of the devices are very promising, the electrical characterizations show large penalty voltage due to the introduction of compensating defects in the p-GaN layers upon plasma etching. Therefore, we consider replacing the p-GaN layers by...

This study examines the effect of (0 0 0 −1) GaN substrate misorientation on the residual impurities and surface morphology of N-polar GaN grown by metalorganic vapor-phase epitaxy. Carbon, silicon, and oxygen concentrations decreased with increasing GaN substrate misorientation angle, with the lowest impurity concentration achieved for a misorient...

Heteroepitaxial growth of single-phase nonpolar (101¯0) m-plane Al x Ga 1-x N layers on m-plane sapphire substrates was investigated by metalorganic vapour phase epitaxy. Different Al/Ga gas phase ratios were used to adjust the AlN mole fraction over the entire range of composition. All m-plane AlGaN layers show an orthorhombic distortion in the wu...

We report here a GaN-based resonant cavity light-emitting diode (RCLED) with top and bottom dielectric TiO 2 /SiO 2 distributed Bragg reflector (DBR) mirrors on a silicon substrate. High data transmission in free space at 200 Mbps with an opening in the eye diagram was achieved. The results show that the combination of GaN-based LED on silicon and...

A simple structure with high breakdown voltage and a low leakage current of a vertical GaN p-n diode on a GaN free-standing substrate is demonstrated. We describe a vertical p-n diode with a simple edge termination that has a drift layer etched deeply and vertically. A device simulation revealed that the electric field was more relaxed at the devic...

The microscopic structural and optical characteristics of AlGaN-based light-emitting diodes grown on AlN templates with macrosteps were evaluated. Cross-sectional transmission electron microscopy in the high-angle annular dark field scanning mode and microscopic energy dispersive X-ray spectroscopy reveal that the AlGaN cladding layer under the AlG...

We present a 286 nm monolithic multicomponent system in which two identical multiple quantum well (MQW) diodes merge with a waveguide together on a single chip. The monolithic multicomponent system allows all existing standard fabrication processes and establishes an optical link between two MQW-diodes because of the simultaneous emission-detection...

Because of their >95% (111) surface orientation and very large (10-300 μm) grain sizes, sub-50 nm Group IV thin films fabricated by metal-induced crystallization are promising seed layers for epitaxy. However, methods for evaluating Group IV film quality for subsequent homo-and heteroepitaxial growth have not been widely reported. Here, we show how...

Light communication: Quantum wells pump up the audio A chip-scale device that uses confined light to emit and detect audio signals simultaneously has been developed by researchers from China and Japan. Recent findings have shown that quantum wells, thin semiconductors films that trap electric charges, can act as light-emitting diodes (LEDs) at the...

Wafer trays with different gaps (the distance between the top of the pocket and the bottom of the wafer) were used to grow InGaN/GaN multiple quantum wells (MQWs) in a horizontal metalorganic vapor phase epitaxy (MOVPE) reactor. The numerical reactor simulation revealed that at the similar surface temperature the gas phase temperature around the wa...

The morphology of thin InGaN layers grown on c-plane GaN substrates by metalorganic vapor phase epitaxy (MOVPE) has been studied by atomic force microscopy. Three different morphologies appeared, a stepped surface, large flat two-dimensional (2D) islands and small high three-dimensional (3D) dots. Low growth temperature and high growth rate (i.e. i...

Transient photoluminescence (PL) characteristics and localization phenomena in InGaN/GaN core-shell nanorods (NRs) were investigated from 6 K up to 285 K. The NRs exhibit three well-defined PL bands in the near-UV, blue, and green range ascribed to the emission of quantum well (QW) areas situated at the (1.00) sidewalls, (10.1) top facets, and (00....

The fabrication of III-nitride semiconductor thin films on substrates such as glass and oxidized Si(001) is of significant interest for LED and CMOS integration applications. However, direct epitaxy on these substrates is difficult because their amorphous structure offers no template for III-nitride thin film growth. In recent work, the growth of...

The full width at half maximum (FWHM) of the luminescence of visible InGaN quantum well (QW) based emitters increases with wavelength. This broadening of the luminescence decreases the color saturation from 100% to about 70% up a wavelength shorter than 515 nm. For emission wavelengths longer than 515 nm, the saturation surprisingly increases again...

We report on the fabrication and optical characterization of monolithically integrated bi- and tri-color micro-LEDs. The different LEDs are successfully stacked during the MOCVD growth and separated afterward by means of dry etching processes. The 100 x 100 m2 active area of the devices is composed of independent subpixels emitting in the blue, gr...

A III-V semiconductor with a few monolayers of alkali metals (e.g., Cs) forms a negative electron affinity (NEA) surface, for which the vacuum level lies below the conduction band minimum of the base semiconductor. The photocathodes that form an NEA surface (NEA photocathodes) have various advantages, such as low emittance, a large current, high sp...

Directional sputtering of Al and AlN on (1 0 −1 0) sapphire was used to obtain metal-polar (1 0 −1 3) templates. After overgrowth with AlN and GaN using metal-organic vapor phase epitaxy, we obtained untwinned (1 0 −1 3) GaN layers. Full width at half maximum of the X-ray rocking curve of symmetric (1 0 −1 3) GaN is less than 550 arcsec along both...

Homogenous InGaN nanowires with a controlled indium composition up to 90% are grown on GaN/c-Al2O3 templates by catalyst-free hydride vapor phase epitaxy using InCl3 and GaCl as group III element precursors. The influence of the partial pressures on the growth rate and composition of InGaN nanowires is investigated. It is shown how the InN mole fra...

Vertical Schottky Barrier Diodes (SBD) were fabricated and the effects of GaN drift-layer thicknesses (DLT) on free-standing GaN substrate were studied. SBDs exhibited average barrier heights (ФB) of 0.72 eV, 0.77 eV and 0.76 eV and ideality factors (n) of 1.1, 1.03, and 1.09 for DLTs of 2 µm, 5 µm and 30 µm, respectively. Decrease of reverse leaka...

The growth of GaN 3-D microstructures is investigated by SAG-HVPE. Capitalizing on the properties of this kinetically-controlled process, the main experimental parameters and physical mechanisms that control the shaping of 3D GaN prisms and pyramids in SAG-HVPE are highlighted. Growth experiments performed on N-polar AlN/Si(100) and Ga-polar GaN/Si...

In this study, we investigate how the duration of trimethylaluminum (TMAl) flow steps used before aluminum nitride (AlN) growth affects the crystal quality of an AlN layer and, in turn, the surface morphologies of a gallium nitride (GaN) layer in a GaN-on-AlN-on-silicon (111) structure. A high pit density was observed on a GaN surface grown under a...

Heteroepitaxial growth of AlN layers on (101¯0) m-plane sapphire substrates was investigated by metalorganic vapour phase epitaxy. Different nucleation temperatures were used to achieve single phase (101¯0) AlN layers. The crystallinity of the layers further increased with increasing annealing temperature and annealing time. The full-width at half...

Non‐polar (m‐plane) gallium nitride (GaN) materials are, unlike their polar (c‐plane) counterparts, free of polarizationinduced charges which make them very promising candidates for the development of high‐performance electronic devices including normally‐off enhancement mode transistors for safe power switching operation and very stable light emit...

Long wavelength nitride LEDs can be realized using InGaN/GaN quantum wells (QWs). However, the low growth temperature and high indium content lead to high defect density, spectral broadening and poor luminescence efficiency. We analyzed the chromaticity of InGaN/GaN QWs covering the visible range, i.e. emitting between 450 and 650 nm. From blue to...

Core-shell nanorods (NRs) are very promising for future optical devices applications. However, such structures are relatively complex, with different facet polarities and local deviations of both QW thickness and indium incorporation. Therefore, a deep understanding of the influence of the core-shell structure on the optical properties is necessary...

An approach to simultaneously grow independent core‐shell structures emitting at different wavelengths by selective area epitaxy is presented. By using seeds of different sizes, the monolithic integration of various GaN crystals including elongated nano‐rods (NRs), micro‐platelets (MPs), and a range of pyramid‐like structures are demonstrated. Domi...

This article describes a new passivation process of Ga2O3, which consists by sputtering, for a vertical GaN p-n junction diode on a free-standing GaN substrate with a field-plate (FP) structure. We demonstrated reduced plasma damage during the sputtering process by cure annealing, and succeeded in improving the breakdown voltage (VB) to -550V with...

Thermal annealing at high temperatures of nonpolar (1 0 1¯ 0) m-plane AlN layers directly sputtered on m-plane sapphire was investigated. The crystallinity of the layers increased with increasing annealing temperature. The full-width at half maximum of the symmetric (1 0 1¯ 0) X-ray rocking curves along [0 0 0 1]/[1 1 2¯0]AlN decreased from about 3...

GaN based micro-rods LEDs are very promising for full-nitride RGB display application. In order to achieve multi-color emissions with high color rendering, the control of the emission from the InGaN grown on the facets of rods is important. We report on the simultaneous growth of various GaN crystals of different shapes by selective area epitaxy....

The reduction of unintentional impurities in m‐plane GaN homoepitaxial layers is demonstrated by using nitrogen (N2), as opposed to hydrogen (H2), as carrier gas in metalorganic vapor phase epitaxy (MOVPE). Secondary ion mass spectrometry (SIMS) analysis shows that the impurity levels of residual oxygen (O), carbon (C), and silicon (Si) are decreas...

We report on the thorough investigation of light emitting diodes (LEDs) made of core-shell nanorods (NRs) with InGaN/GaN quantum wells (QWs) in the outer shell, which are grown on patterned substrates by metal-organic vapor phase epitaxy. The multi-bands emission of the LEDs covers nearly the whole visible region, including UV, blue, green, and ora...

Hexagonal boron nitride (h-BN) films directly grown on c-plane sapphire substrates by pulsed-mode metalorganic vapor phase epitaxy exhibit an interlayer for growth temperatures above 1200 °C. Cross-sectional transmission electron microscopy shows that this interlayer is amorphous, while the crystalline h-BN layer above has a distinct orientational...

A monolithic near-ultraviolet multicomponent system is implemented on a 0.8-mm-diameter suspended membrane by integrating a transmitter, waveguide, and receiver into a single chip. Two identical InGaN/Al0.10Ga0.90N multiple-quantum well (MQW) diodes are fabricated using the same process flow, which separately function as a transmitter and receiver....

A gallium nitride (GaN) epitaxial layer with a low density of threading dislocations was successfully grown by Matsumoto et al. (article no. 1700387) on a silicon substrate by using in‐situ gas etching. Silicon nitride (SiNx) film was used as a mask, and ammonia was intermittently supplied in hydrogen ambient during the etching. High‐density deep p...

Dislocations that cause a reverse leakage current in vertical p-n diodes on a GaN free-standing substrate were investigated. Under a high reverse bias, dot-like leakage spots were observed using an emission microscope. Subsequent cathodoluminescence (CL) observations revealed that the leakage spots coincided with part of the CL dark spots, indicati...

The main chain structure of optically isotropic amorphous fluorine resin for encapsulating AlGaN-based deep-ultraviolet LEDs (λ < 300 nm) is studied. One type of amorphous fluorine resin has a five-membered ring with a single oxygen atom and the other has that one with two oxygen atoms. Reliability testing is performed using AlGaN-based LEDs of 262...

Microrod based light emitting diodes have been realized by selective area epitaxy with MOCVD. Electroluminescence characterization of the devices shows a broad luminescence composed of several distinct emissions from blue to orange which are commonly related to the different side facets. TEM and further optical analysis questioned the origin of the...

In this study, GaN m-plane Schottky barrier diodes are fabricated by metalorganic vapor-phase epitaxy (MOVPE) on several off-angle gallium nitride (GaN) substrates, and the off-cut angle dependence of impurity incorporation is investigated. We show that the MOVPE layer on the substrate inclined 5° toward the [000–1] direction has extremely low impu...

A gallium nitride (GaN) epitaxial layer with a low density of threading dislocations is successfully grown on a silicon substrate by using in situ gas etching. Silicon nitride (SiNx) film is used as a mask, and ammonia is intermittently supplied in hydrogen ambient during the etching. After etching, high-density deep pits appeared on the surface of...

The carbon incorporation mechanism in GaN(0001) and GaN(0001¯) during MOVPE was investigated using density functional theory (DFT) calculations. The results confirm that the crucial factors for carbon incorporation are Fermi level pinning and accompanying surface band bending. In addition, the lattice symmetry has a strong dependence on the stabili...

Hexagonal boron nitride (h-BN) was directly grown on sapphire substrate using alternating ammonia (NH3) and triethylboron (TEB) supply (pulsed mode) in metalorganic vapor phase epitaxy. The best condition is when just enough NH3 is supplied to fully convert the TEB within one cycle. Excess NH3 caused islands on h-BN film surface while a lack of NH3...

Electrical characteristics of leakage current paths in vertical-type n-GaN Schottky barrier diodes (SBDs) on free-standing GaN substrates are investigated by using photon emission microscopy (PEM). The PEM mapping shows that the initial failure of the SBD devices at low voltages is due to the leakage current paths from polygonal pits in the GaN epi...