A5060324422- GaN-based semiconductor devices and materials
- Semiconductor materials and devices
- Ga2O3 and related materials
- Silicon Carbide Semiconductor Technologies
- ZnO doping and properties
- Metal and Thin Film Mechanics
- Advanced Photocatalysis Techniques
- Acoustic Wave Resonator Technologies
- Advanced ceramic materials synthesis
- Molecular spectroscopy and chirality
- Chalcogenide Semiconductor Thin Films
- Photoreceptor and optogenetics research
- Silicon Nanostructures and Photoluminescence
- Semiconductor Quantum Structures and Devices
- Electronic and Structural Properties of Oxides
- Semiconductor materials and interfaces
- Silicone and Siloxane Chemistry
- Glycosylation and Glycoproteins Research
- Advanced Optical Sensing Technologies
- Advanced Surface Polishing Techniques
- Optical Coatings and Gratings
- Photocathodes and Microchannel Plates
- Phase-change materials and chalcogenides
- Copper Interconnects and Reliability
- solar cell performance optimization
University of Tsukuba
2016-2024
Massachusetts Institute of Technology
2017-2019
École Polytechnique Fédérale de Lausanne
2016
Kyoto University
2008-2014
University of California, Santa Barbara
2014
Meiji University
2001
This letter demonstrates vertical GaN junction barrier Schottky (JBS) rectifiers fabricated with novel ion implantation techniques. We used two different methods to form the lateral p-n grids below contact: 1) Mg into n-GaN p-wells and 2) Si p-GaN n-wells. Specific differential ON-resistances ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{ \mathrm{\scriptscriptstyle ON}}$...
β-Ga2O3(010) homo-epitaxial growth was performed by plasma-assisted molecular beam epitaxy. Under Ga-rich conditions and for temperatures above 650 °C, the rate independent of Ga/O ratio (>1). A high 2.2 nm/min achieved optimizing O flux between 750 °C. 500–900 smooth surfaces with rms roughness below 1 nm were realized. We found that slightly °C optimal a surface rate.
We report on the electrical characterization of Si-ion implanted AlN layers and first demonstration metal–semiconductor field-effect transistors (MESFETs) with an ion-implanted channel. The Si dose 5 × 1014 cm−2 exhibit n-type characteristics after thermal annealing at 1230 °C. MESFETs provide good drain current saturation stable pinch-off operation even 250 off-state breakdown voltage is 2370 V for drain-to-gate spacing 25 µm. These results show great potential AlN-channel high-temperature...
Abstract We investigated dry and wet etchings of β -Ga 2 O 3 fabricated vertical Schottky barrier diodes (SBDs) with mesa termination using the optimal etching condition. Using an inductively-coupled plasma reactive-ion a nickel-hard mask, (010) structure smooth sidewall is obtained at rate 77 nm min −1 in BCl /Cl mixture gas. By immersing (001) SBDs hot phosphoric-acid solution, specific on resistance ideality factor are reduced to 0.91 mΩcm 1.03, respectively. Current density reverse bias...
This paper demonstrates a modulation-doped fisseld-effect transistor (MODFET) and metal-semiconductor field-effect (MESFET) using β-(AlGa)2O3 (010). Ohmic contacts on Sn-doped (Al0.15Ga0.85)2O3 exhibit fairly linear behavior, which has specific contact resistivity sheet resistance of 9 × 10−5 Ω cm2 75 kΩ/□, respectively. The MODFET with (Al0.08Ga0.92)2O3 barrier layer showed breakdown voltage 610 V for gate-drain spacing (Lgd) 8 μm, while the (Al0.16Ga0.85)2O3-channel MESFET exhibited 940...
This letter reports the demonstration of N-polar Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.8</sub> Ga xmlns:xlink="http://www.w3.org/1999/xlink">0.2</sub> N/AlN continuously-graded-channel polarization-doped field-effect transistors (PolFETs) on SiC. A PolFET with a source to drain distance 12 μm exhibited maximum current 62.8 mA/mm and an ON/OFF ratio 1.1 × 10 <sup xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> . The was stable...
Abstract We reported the growth of (AlGa) 2 O 3 layers on (11 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mn>2</mml:mn> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> 0), (10 <mml:mn>1</mml:mn> and 2) α -Al substrates using MBE, electrical characterization Si-doped layers. The Ga grown 0) were -phase single crystals, while layer consisted -Ga ( 01) β . Al composition was controlled by varying flux. -(Al x 1- ) with = 0–0.41...
300-nm-thick AlN layers were grown directly on 6H-SiC(0001) with six Si–C bilayer-height (1.5 nm) steps by rf-plasma-assisted molecular-beam epitaxy (MBE). To avoid unintentional active-nitrogen exposure, was just after the nitrogen plasma ignition. By combining optimized Ga pre-deposition and no layer-by-layer growth realized from first layer of AlN. Screw-type edge-type threading dislocation densities in reduced to 6×104 4×108 cm-2, respectively. Most dislocations located at step edge SiC...
We grew heavily Mg-doped GaN using ammonia molecular-beam epitaxy. The use of low growth temperature (740 °C) allows decreasing the incorporation donor-like defects (&lt;3 × 1017 cm−3) responsible for p-type doping compensation. As a result, net acceptor concentration 7 1019 cm−3 was achieved, and hole measured by Hall effect as high 2 at room temperature. Using such Mg level, we fabricated backward diodes without polarization-assisted tunneling. exhibited tunneling-current density 225...
Abstract Radiation tolerance of Cu(In,Ga)Se 2 (CIGS) solar cells has been investigated using high-fluence proton beam irradiation for application to devices in extremely-high-radiation environments. CIGS deteriorated after high-energy with non-ionizing energy loss 1 × 10 16 MeVn eq cm −2 , however, the could generate power irradiation. The ideality factors increased from 1.3 2.0, and series resistance increased, indicating that concentration recombination centers layers. After heat-light...
We report on the critical thickness of AlN SiC(0001). was directly grown 6H-SiC(0001) at 650 °C by rf-plasma-assisted molecular beam epitaxy. The growth layer had a relatively low threading dislocation density 4×108–4×109 cm-2. Although SiC(0001) is estimated to be 3.5 nm using Matthews–Blakeslee model, in our experiment over 700 nm. Low density, layer-by-layer mode, and temperature may contribute such large thickness. Sharp intense free exciton emission observed low-temperature PL...
Abstract AlN with a large bandgap energy is one of the most attractive materials for high-temperature applications. However, performance devices at high temperatures has been limited by technical problems electrical characterization systems. Here, we show that Schottky-barrier diodes (SBDs) and metal-semiconductor field-effect transistors Si-implanted channels can operate 1100 K 1000 K, respectively. The breakdown voltage barrier height SBD were 610 V 3.5 eV, We found thermal stability Ni...
N-face GaN was grown on free-standing (0001¯) substrates at a growth rate of 1.5 μm/h using plasma-assisted molecular beam epitaxy. Difference in between and (0001) oriented depends nitrogen plasma power, the had only 70% 300 W. Unintentional impurity concentrations silicon, carbon, oxygen were 2 × 1015, 1016, 7 1016 cm−3, respectively. A diagram constructed that shows dependence modes difference Ga active flux, ΦGa − ΦN*, temperature. At high ΦN* (ΦGa ≫ ΦN*), two-dimensional (step-flow...
In this work, p-type cuprous oxide (Cu2O) films grown on beta gallium (β-Ga2O3) substrates by magnetron sputtering were reported. The resulting vertical Cu2O/β-Ga2O3 heterojunction p–n diodes demonstrated superior performance compared to devices fabricated with polycrystalline Cu2O thin films. Meanwhile, analysis of the discrepancies between built-in potential and turn-on voltage revealed diverse carrier transport mechanisms in devices. Numerical fitting forward J–V characteristics further...
We present the electrical characterization of N-polar AlN layers grown by metal-organic vapor phase epitaxy and demonstration AlN-channel metal-semiconductor field-effect transistors (MESFETs). A high concentration silicon is unintentionally incorporated during high-temperature growth AlN, causing buffer leak current. The reduces from 2x10^18 /cm^3 to 9x10^15 with decreasing temperature, reducing current 5.6 nA/mm at a 100 V bias. MESFET exhibits an off-state drain 0.27 transistor on/off...
Abstract We report on impurity diffusion in ion implanted AlN layers after thermal annealing. Silicon, tin, germanium, and magnesium ions were into single-crystal Al-polar grown sapphire substrates. By annealing at 1600 °C, silicon atoms diffused the layer, while less change was observed distribution of germanium atoms. Silicon implantation introduced vacancy-related defects. temperatures over 1300 defects reduced, oxygen from substrate due to decomposition. reproducibly achieved...
Abstract Solid-state materials with a large bandgap energy have potential for high-temperature, high-power, radiation-hardened, and ultraviolet-light applications. α -Al 2 O 3 , of ∼9 eV, is one the most attractive such materials. However, suffers from high resistivity. Here, we show that heavily Si-doped (10 <?CDATA $\bar{1}$?> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mn>1</mml:mn> <mml:mo>¯</mml:mo> </mml:mover> </mml:math>...
We grew AlN layers on 6H-SiC (0001) substrates with three Si-C bilayer high (0.75 nm) steps. In the layers, most of threading dislocations (TDs) were arranged in rows. The TD row consisted arrays a half-loop dislocation, which was formed by an AlN/SiC interfacial dislocation along step edges SiC substrate surfaces and pair at both ends. configuration highly relevant two-dimensional nuclei initial stage growth. concluded that generated nucleus coalescence over edges.
In this work, interface traps in β-(AlGa)2O3/Ga2O3 modulation-doped field effect transistor (MODFET) were investigated qualitatively and quantitatively by means of dynamic capacitance dispersion technique. The fabricated MODFET showed drain current modulation demonstrating the behavior. existence two-dimensional electron gas was confirmed plateau region capacitance–voltage (C–V) characteristics. difference profile at multifrequency C–V measurement suggested loss mechanism due to trapping...
The optical properties of wurtzite AlN under large compressive strain are investigated by photoluminescence and reflectivity measurements with two different geometries. layer was coherently grown on 6H-SiC(0001), resulting in strains εxx=εyy=-9.6×10-3 εzz=5.12×10-3, as confirmed high-resolution X-ray diffraction. Free exciton transitions were clearly observed. transition energy A free (with Γ1 symmetry) estimated to be 6.246 eV at 10 K. shift the respect unstrained well explained reported...
Abstract 300‐nm‐thick AlN layers without a nucleation layer were grown on 6H‐SiC (0001) vicinal substrates with 3‐bilayer‐height steps by rf‐plasma‐assisted molecular‐beam epitaxy. A Ga beam was supplied for 0 to 30 seconds just before growth of AlN. The pre‐irradiation 7 (∼1.6 ML) found be effective realization the layer‐by‐layer mode at an earlier stage and reduction threading dislocation densities (TDD) in layers. screw‐type edge‐type TDDs ∼10 6 cm ‐2 6×10 8 , respectively. (© 2010...
Mg-doped GaN with a net acceptor concentration (NA-ND) in the high 1019 cm−3 range was grown using ammonia molecular-beam epitaxy. Electrical properties of NiO contact on this heavily doped p-type were investigated. A potential-barrier height 0.24 eV extracted from relationship between NA-ND and specific resistivity (ρc). We found that there is an optimum value 5 × for which ρc as low 2 10−5 Ω cm2. This ascribed to hole tunneling through potential barrier at NiO/p+-GaN interface, well...