Makoto Miyoshi

Nagoya Institute of Technology · Research Center for Nano-Devices and Advanced Materials

In this study, the operation of npn-type GaN-based heterojunction bipolar transistors with different net acceptor concentrations in p-base regions was simulated. It was confirmed that there is a critical net acceptor concentration (NA-ND) depending on the thickness of the base region and that if the NA-ND is lower than the critical value, the colle...

In this study, we investigated the effect of inserting a 1-nm-thick AlN thin-film layer in the drift layer of a GaN-on-Si Schottky barrier diode (SBD) to improve the reverse-bias breakdown voltage. The breakdown voltage was significantly improved from 258 V (without an AlN layer) to 338 V (with an AlN layer placed at the bottom of the drift layer),...

A high‐electron‐mobility transistor (HEMT) structure consisting of a strain‐engineered quaternary AlGaInN barrier layer on an unintentionally‐doped (UID) GaN channel layer was grown on a single‐crystal (SC) AlN substrate by metalorganic chemical deposition and subjected to the device fabrication and characterization. DC static measurement results s...

To accomplish a high-temperature operation of GaN/InGaN multiple-quantum-well (MQW) UV photodetectors (UV-PDs), the investigation of device performances at high-temperature regimes is truly essential. Therefore, in the present work, GaN/InGaN MQW-based UV-PDs on sapphire are fabricated and their photovoltaic and carrier transit time characteristics...

Semipolar {112̄2} AlInN layers with thicknesses of approximately 0.4 μm were grown on a fully‐relaxed semipolar Ga0.9In0.1N/GaN/m‐plane sapphire template by metalorganic chemical vapor deposition. The grown AlInN layers were confirmed to have relatively flat surfaces of less than 1.5 nm in root mean square roughness and high InN mole fractions rang...

Lattice-matched Al1−xInxN / GaN heterostructures with InN mole fraction (x) of 0.18 have attracted considerable interest for use in GaN-based optoelectronic devices. Because the light emission efficiency (ηemission) of Al1−xInxN alloys is far less than that of InxGa1−xN, understanding its causes is essential. For this purpose, room-temperature phot...

To examine the critical role of electrically active defects and surface states in InGaN/GaN multiple quantum well (MQW) ultraviolet photodetectors (UV-PDs), the study of degradation mechanisms in such devices is very important. In this work, we have fabricated InGaN/GaN MQW UV-PDs with a thick passivation layer of Al2O3 and studied their degradatio...

To improve the performance of GaInN/GaN multiple quantum wells (MQW) ultraviolet photodetectors (UV-PDs), the thickness of p-GaN layer plays an important role. Thereby, to see the impact of p-GaN layer thickness on epilayer quality and device performances, in the present work, we fabricated two different sets of GaInN/GaN MQW-based UV-PDs by varyin...

In this study, we fabricated and characterized heterojunction field-effect transistors (HFETs) based on an Al 0.36 Ga 0.64 N-channel heterostructure with a dual AlN/AlGaInN barrier layer. The device fabrication was accomplished by adopting a regrown n ⁺⁺ -GaN layer for ohmic contacts. The fabricated HFETs with a gate length of 2 μm and a gate-to-dr...

Herein, a simulation study on novel GaN‐based n−p−n heterojunction bipolar transistors (HBTs) with a quaternary n‐AlGaInN emitter and a thin GaInN quantum well (QW) layer inserted in its p‐GaN base is reported. The idea of the quaternary AlGaInN emitter facilitates the design and independent growth of the energy bandgaps and lattice strain. In addi...

Transfer-free graphene synthesis was performed using the catalyst metal agglomeration technique. X-ray diffraction and electron backscattering diffraction measurements indicated that the quality of the Ni catalyst film was enhanced with the increase of the crystallite size of Ni (111) by heating treatments during and following Ni deposition. Moreov...

Al0.19Ga0.81N-channel metal-insulator-semiconductor heterojunction field-effect transistors (MIS-HFETs) with a quaternary AlGaInN barrier layer and a selectively regrown n⁺⁺-GaN contact layer were fabricated using the self-alignment selective-area growth (SAG) technique. The self-alignment SAG process was accomplished by the local-area etching proc...

GaInN-based photovoltaic (PV) devices are highly promising for application to optical wireless power transmission (OWPT) systems as well as solar cells. This paper reports the research results of Ga0.9In0.1N multiple-quantum-well (MQW) PV cells on sapphire, focusing primarily on the growth temperature managements in metalorganic chemical vapor depo...

A record-long room-temperature photoluminescence (PL) lifetime (τPLRT) of approximately 70 ps was obtained for the sub-bandgap 3.7 eV emission band of a 300-nm-thick c-plane Al0.83In0.17N epilayer for the use in cladding layers of an edge laser structure, which were grown by metalorganic vapor phase epitaxy on a low threading dislocation density ne...

The impact of growth temperature (GT), in the range from 875 to 825 °C, on the morphological, structural, electrical, and optical properties of InGaN/GaN multiple quantum well ultraviolet photodetectors (UV-PDs) is investigated. Lowering of GT is found to increase In composition in the well layers and deteriorates surface and crystalline quality as...

We investigated the relationship between the optical constants and localized states near the band-edge in high-quality crystalline Al 1− x In x N alloys, with an indium content x ranging from 0.12 to 0.22, grown on a c -plane freestanding GaN substrate. Optical constants were obtained by spectroscopic ellipsometry. The tanΨ and cosΔ spectra were fi...

GaN-based p–i–n ultraviolet photodetectors (UV-PDs) with a 20 nm thick Al2O3 passivation layer are fabricated and the photocurrent generation mechanisms of the device at different biases are studied by performing different electro-optical measurements. Our UV-PDs reveal good rectifying current–voltage behavior but their generated photocurrent to UV...

The degradation characteristics of InGaN/GaN multiple quantum well (MQW) photodetectors (PDs) stressed at 100 and 200 mA over 480 h are investigated. We have observed that the luminescence intensity, short circuit current density, and open circuit voltage decrease strongly, whereas the leakage current increases intensely due to the constant current...

This Letter reports the polarization induced hole conduction in composition-graded AlInN epitaxial layers grown by metalorganic chemical vapor deposition. First, the composition-graded AlInN layer with an InN mole fraction from 0.12 to 0.20 was formed on c-plane GaN on sapphire, and they were confirmed to show the p-type hole conduction with a less...

Metalorganic chemical vapor deposition of approximately 300-nm thick epitaxial AlInN films with different alloy compositions was performed using a semi-relaxed c-plane GaInN template as an underlying substrate. The GaInN template consisted of a Ga0.98In0.02N film on a facet-structured GaN film formed on a c-plane sapphire substrate by the epitaxial...

The impact of defects on the degradation behaviors of InGaN/GaN multiple-quantum-well photodetectors submitted to dc current stress has been intensively studied. The root mechanism for degradation has been studied employing combined electro-optical measurements. The collected results indicate that (i) stress can induce an increase in parasitic curr...

Correlations between the structural properties and nonradiative recombination (NRR) behaviors of threading dislocations in freestanding hydride-vapor-phase-epitaxy (HVPE) GaN substrates were investigated using cathodoluminescence (CL), the etch pit method, transmission electron microscopy (TEM), and multiple-photon excitation photoluminescence (MPP...

A comprehensive analysis of the degradation behavior of (In)AlGaN-based deep-ultraviolet light-emitting diode (DUV LED) stressed at a constant dc current of 60 mA has been presented. This work is based on combined X-ray diffraction (XRD), atomic force microscopy (AFM), electroluminescence (EL), cathodoluminescence (CL), current-voltage (I–V) and ca...

In this study, Si-doped conductive AlInN films with a thickness of 300 nm were grown nearly lattice-matched to c-plane GaN-on-sapphire templates by metalorganic chemical vapor deposition. A high net donor concentration of approximately 1 × 10¹⁹ cm⁻³ was observed for a highly Si-doped AlInN film. To evaluate its vertical-direction electrical resisti...

Quaternary AlGaInN films with a film thickness of greater than 150 nm were grown on a c‐plane GaN‐on‐sapphire templates by metalorganic chemical vapor deposition (MOCVD). The AlxGayInzN films near alloy compositions lattice‐matching to GaN on sapphire (0.532 ≤ x ≤ 0.716, 0.146 ≤ y ≤ 0.366, and 0.092 ≤ z ≤ 0.182) were confirmed to be epitaxially gro...

In this study, Al2O3-gate-insulated metal-insulator-semiconductor (MIS) heterostructure field-effect transistors (HFETs) were fabricated using an Al0.61Ga0.37In0.02N/Al0.18Ga0.82N two-dimensional-electron-gas heterostructure, and their electrical properties were characterized. It was confirmed that the thermally stable quaternary AlGaInN barrier la...

We investigated and improved optical waveguides along the vertical and horizontal directions in 450 nm GaInN laser diodes. As a result, we demonstrated a low threshold current density (1.15 kA cm ⁻² ) of a GaInN ridge stripe laser diode containing a 3-pair 40 nm Al 0.82 In 0.18 N/25 nm Al 0.03 Ga 0.97 N multiple bottom cladding layer at room temper...

Single-layer AlInN films with a film thickness of approximately 300 nm were grown on a c-plane free-standing (FS) GaN substrate by metalorganic chemical vapor deposition. The result showed that a highly flat-surface AlInN film with a small root-mean-square surface roughness of less than 0.5 nm was realized by adjusting its alloy composition to an a...

In order to improve the thermal stability in AlGaN-channel two-dimensional electron gas (2DEG) heterostructures, we newly designed strain-controlled quaternary AlGaInN barrier layers, and then we grew them by metalorganic chemical vapor deposition. A 2DEG density as high as 2.5 × 10¹³ cm⁻² and a good surface morphology were obtained for an (Al0.64G...

We propose an innovative ultrathin AlGaN/InAlN heterojunction (HJ) inserted in AlGaN-based deep ultraviolet light-emitting diode (DUV LED) structure. Theoretical investigations indicate that the AlGaN/InAlN HJ is quite beneficial to suppress electron leakage and improve hole injection. These boosted characteristics strengthen the radiative recombin...

300-nm-thick AlInN films with InN molar fractions ranging from 0.114 to 0.197 were grown by metalorganic chemical vapor deposition on c-plane GaN on sapphire. It was confirmed that no lattice relaxation occurred for samples with InN molar fractions from 0.144 to 0.197, and the InAlN films with low InN molar fractions showed a relative smooth surfac...

AlInN epitaxial films with film thicknesses up to approximately 300nm were grown nearly lattice-matched to a c-plane GaN-on-sapphire template by metalorganic chemical vapor deposition. The AlInN films showed relative good crystal qualities and flat surfaces, despite the existence of surface pits connected to dislocations in the underlying GaN film....

We attempted to improve the mobility of InAlN/AlGaN two-dimensional electron gas (2DEG) heterostructures by achieving an atomically smooth heterointerface in metalorganic chemical vapor deposition processes. In the result, it was confirmed that the high-growth-rate AlGaN layer was very effective to improve the surface morphology. The atomically smo...

We report on distinct light emission from two-dimensional electron gas (2DEG) at a lattice-matched (LM) In0.12Al0.88N/Al0.21Ga0.79N heterointerface. The recombination between the electrons in the 2DEG in the ground state E1 and photoexcited holes in the Al0.21Ga0.79N layer was identified. In contrast to GaN channel-based heterostructures (HSs), lar...

Two kinds of substrates, sapphire and AlN/sapphire template (AlN template), are used for the growth of InGaN/GaN multi-quantum-well solar cell structures by metalorganic chemical vapor deposition, and their material and device properties are investigated. The results show that the samples grown on AlN template have a better crystal quality with a l...

We report on the fabrication and characterization of AlGaN-based PiN type UV photodiodes with and without the surface recessed electrode structures. It was confirmed that the device with the surface recessed structure showed a much higher responsivity of 202 mA/W at a wavelength of 272 nm under a reverse bias voltage of -5 V than that of the device...

We demonstrate high-performance ultraviolet photodetectors (UV-PDs) based on lattice-matched (LM) InAlN/AlGaN heterostructure field-effect transistors (HFETs) gated by transparent ITO films. Low dark currents of 6.8 × 10⁻⁸ and 6.1 × 10−7 A/mm and high photocurrent gains over four and three orders of magnitude were obtained for the LM In0.12Al0.88N/...

We conducted the study on the growth of rough-surface p-GaN layers on InGaN/GaN multiple-quantum-well (MQW) structures by metalorganic chemical vapor deposition (MOCVD). It was found that the sum of InGaN well thickness t well_total was a predominant factor to form the rough surface, in addition to the growth temperature as low as 800 °C for the p-...

The effects of post-deposition annealing (PDA) on Al2O3/AlGaN interfaces fabricated by atomic layer deposition (ALD) are studied by x-ray photoelectron spectroscopy (XPS) using synchrotron radiation. Current-voltage (I-V) measurements of annealed Al2O3/AlGaN/GaN metal-insulator-semiconductor (MIS)-type high electron mobility transistors (HEMTs) on...

We investigated the effect of well layer thicknesses on the external quantum efficiency (EQE) and energy conversion efficiency (ECE) for InGaN/GaN multiple quantum well (MQW) solar cells grown on sapphire substrates by metalorganic chemical vapor deposition. The results indicated that EQE and ECE have maximum values at a specific well thickness. Wh...

A normally-Off metal-oxide-semiconductor field-effect transistor (MOS-FET) is proposed by using AlInN/AlGaN heterostructure grown on silicon. The AlGaN channel MOSFET with Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http:...

We fabricated graphene/Ni patterns directly on sapphire substrates through a self-forming process utilizing the pattern-controlled catalyst metal agglomeration technique, which was accomplished via a thermal annealing process of rectangular Ni patterns preformed on thin amorphous carbon films on sapphire. It was confirmed that graphene films were s...

Dislocation reaction in a GaN layer grown on 4-inch Si(111) with AlGaN/AlN strained layer superlattice was observed by transmission electron microscopy. The reaction between a dislocation (b=1/3[1–210]) and another dislocation (b =1/3[11–20]) to form a dislocation segment (b =1/3[2-1-10]) was demonstrated by plan-view observation using weak-beam da...

We built a calculation model for the wafer bow in GaN-on-Si epiwafers employing GaN/AlN multilayer (ML) buffer structures by extending Stoney's equation. The calculated bow and the derived strain in the epilayers were almost consistent with experimental results. The calculation quantitatively revealed that the ML buffers introduced an in-plane comp...

A nearly lattice-matched In0.12Al0.88N/Al0.21Ga0.79N heterostructure field-effect transistor (HFET) was fabricated and its device characteristics were evaluated. The fabricated device showed good pinch-off characteristics with a high breakdown field of 118 V/μm. A simple device calculation based on the experimental results showed the possibility th...

Remarkably enhanced light emission efficiency of AlGaN multiple quantum wells (MQWs) was realized by growing on an n-AlGaN underlying layer (UL). The parasitic peaks emitting from inactive regions can be effectively suppressed, and the nonradiative recombination process in AlGaN MQWs was proved to be substantially lessened with the inclusion of the...

A 6H-SiC substrate with femtosecond-laser-induced periodic nanostructures was used as an underlayer for GaN growth. GaN nuclei were formed on the periodic nanostructure selectively. The in-plane direction of GaN was dependent on the in-plane direction of the SiC substrate, and no dependent on the direction of the periodic nanostructures or laser sc...

The surface passivation for InGaN/GaN multilayer solar cells was investigated, and it was confirmed that the device with an atomiclayer-deposited (ALD) Al2O3 passivation film showed high internal and external quantum efficiencies of 99 and 84%, respectively, along with a high energy conversion efficiency of 1.31% under a 1-sun airmass 1.5 global il...

Dislocations in a GaN layer grown on 4-in. Si(111) with AlGaN/AlN strained layer superlattices using a horizontal metal–organic chemical vapor deposition system were characterized by transmission electron microscopy and scanning transmission electron microscopy. Pure screw dislocations were not found in the observed area but mixed and edge dislocat...

The behavior of dislocations in a GaN layer grown on a 4-inch Si(111) substrate with an AlGaN/AlN strained layer superlattice using horizontal metal-organic chemical vapor deposition was observed by transmission electron microscopy. Cross-sectional observation indicated that a drastic decrease in the dislocation density occurred in the GaN layer. T...

We demonstrate notable performance improvement of 270 nm deep ultraviolet light-emitting diodes (DUV-LEDs) by inserting an n-AlGaN underlayer (UL), which was directly beneath an AlGaN multiple quantum well (MQW) active region. This DUV-LED exhibited significantly improved forward and reverse bias current-voltage characteristics, and spectral proper...

Transfer-free graphene synthesis was performed on sapphire substrates by using the catalyst metal agglomeration technique, and the graphene film quality was compared to that synthesized on sputtered SiO2/Si substrates. Raman scattering measurements indicated that the graphene film on sapphire has better structural qualities than that on sputtered S...

Two-dimensional electron mobilities in AlGaN-channel nitride heterostructures were numerically and experimentally analyzed. The calculation and experimental results indicated that mobility for InAlN/AlGaN heterostructures grown by metalorganic chemical vapor deposition was limited by interface roughness scattering as well as alloy disorder scatteri...

Nearly lattice-matched InAlN/AlxGa1-xN (x = 0.1, 0.21, and 0.34) heterostructures with a 1-nm-thick AlN interfacial layer were grown on AlN/sapphire templates by metalorganic chemical vapor deposition. Capacitance voltage and Hall effect measurements revealed that two-dimensional electron gases (2DEGs) with high densities exceeding 2 x 10(13)/cm(2)...

In this study, planar Pd/ZnO/GaN heterojunction diodes (HJDs) are fabricated and their capabilities for NOx (NO and NO2) gas-sensing is evaluated. The fabricated HJDs exhibit good rectifying properties at a high temperature of 250 °C and, in addition, they exhibit obvious current changes even under low-concentration 10 ppm NOx gases and respond to...

Transfer-free graphene synthesis process utilizing metal agglomeration phenomena was investigated by using carbon films deposited on Ni or Co catalyst metals on SiO2/Si substrates. As a result of metal agglomeration at high temperatures, multilayer graphene films appeared to be formed directly on SiO2 films. The microscopic Raman mapping study reve...

Different-indium-content quaternary InAlGaN multi-quantum-well (MQW) structures with emission wavelength around 290–310 nm were grown by metalorganic chemical vapor deposition, and their emission characteristics including the indium-segregation effect were investigated by using not only experimental evaluation but also applying simulation technique...

Graphene layers were synthesized by annealing amorphous carbon (a-C) thin films on Ni/SiO2/Si(111) substrates grown using pulse arc plasma deposition. Although the graphene layers were formed by catalytic reaction between a-C films and Ni metals, they were observed to be directly on the insulating SiO2/Si substrates with island-shaped metallic part...

An underlying film 2 of a group III nitride is formed on a substrate 1 by vapor phase deposition. The substrate 1 and the underlying film 2 are subjected to heat treatment in the present of hydrogen to remove the underlying film 2 so that the surface of the substrate 1 is roughened. A seed crystal film 4 of a group III nitride single crystal is for...

The authors demonstrate AlGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs) on high-quality AlN/sapphire template (AlN template) by evaluating its characteristics. LED structures can be grown directly on 2-in.-diameter AlN template by metal-organic chemical vapor deposition. AlGaN epilayers are confirmed to have high crystal quality on Al...

InAlN/GaN epilayer on AlN/Sapphire template was grown by metalorganic chemical vapor deposition (MOCVD) with a very high electron sheet carrier density n(s) = 2.6 x 10(13) cm(-2) and a Hall mobility as high as mu(Hall) = 1170 cm(2) V(-1) s(-1) at room temperature. The electrical characteristics of the fabricated high-electron-mobility transistors (...

The origin and suppression of the subband parasitic peak in AlGaN deep ultraviolet light-emitting diodes have been studied. The parasitic peak is clarified to come from a p-AlGaN cladding layer and to be related to Mg dopants. By using 1 nm i-AlN as an interlayer between the active region and the p-AlGaN cladding layer, this peak is suppressed effi...

InAlN/GaN two-dimensional electron gas (2DEG) heterostructures were successfully grown by metalorganic chemical vapor deposition. X-ray photoelectron spectroscopy and X-ray diffraction measurements revealed that the barrier layer consists of a ternary In0.18Al0.82N alloy, a composition nearly lattice-matched to GaN. The bandgap energy of the In0.18...

The behavior of electroluminescence (EL) and junction temperature of AlInGaN deep ultraviolet light-emitting diodes under pulse-width modulation is investigated. The redshift of both emissions from quantum-well (P1) and localized (P2) states in the EL spectra and the increase of intensity ratio of P1 to P2 are observed with the increase of duty cyc...

AlGaN-based multiple-quantum-well light-emitting diodes (LEDs) with peak emission at UV-C region of 264 nm were successfully gown on AlN template using metal organic chemical vapour deposition. It was found that a subband emission around 320 nm can be drastically reduced by inserting a thin 1 nm-thick AlN interlayer between the active region and p-...

AlGaN films and deep ultraviolet light-emitting diode (UV-LED) structures with AlGaN multi-quantum wells (MQWs) were grown directly on 2-in.-diameter epitaxial AlN/sapphire template (AlN template) by metalorganic chemical vapor deposition (MOCVD). It was confirmed that crack-free and good-crystal-quality AlGaN films and UV-LED structures can be gro...

Injection current and temperature dependence of electroluminescence (EL) is investigated in AlInGaN deep untraviolet light-emitting diodes. Two EL bands with different behaviors are observed. The high-energy band (P1) shows a monotonous redshift and an amazing increase of intensity with increasing current, however, a “U”-shaped shift and a saturati...

Pt Schottky diodes were fabricated on high-crystal-quality Al0.2Ga0.8N/GaN epitaxial films grown using epitaxial AlN/sapphire template (AlN template), and their current transport characteristics were measured and analyzed. It was confirmed that reverse leakage currents in Schottky diodes formed on AlN template were drastically reduced compared with...

AlGaN/GaN-based planer Schottky barrier diodes (SBDs) with circular anode configuration were formed on AIN template and on sapphire. SBDs formed on AIN template exhibited clearly improved reverse-blocking characteristics compared with SBDs formed on sapphire. This appears to be due to their high crystal quality realised as a result of using AIN tem...

Buried gate type p-base n-emitter soft contact (PNSC) structure 4 kV static induction thyristors (SIThys) have been fabricated in order to make thyristors for high-speed turn-on applications to such as high energy accelerators. It was found that these static induction thyristors could be fabricated under the test pilot line with a good device produ...

Al0.26Ga0.74N/AlN/GaN high-electron-mobility transistor (HEMT) structures with AlN interfacial layers of various thicknesses were grown on 100-mm-diameter sapphire substrates by metalorganic vapor phase epitaxy, and their structural and electrical properties were characterized. A sample with an optimum AlN layer thickness of 1.0nm showed a highly e...

Al0.26Ga0.74N/AlN/GaN heterostructures with a 1 nm-thick AlN interfacial layer were grown on epitaxial AlN/sapphire templates by metal-organic vapor phase epitaxy, and they exhibited excellent film qualities and very high electron mobilities, such as over 2100 cm2/V s at room temperature and over 25 000 cm2/V s at 15 K with a two-dimensional electr...