Faculty Profiles - AMANO, Hiroshi

Papers - AMANO, Hiroshi

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Multiplexing of bias-controlled modulation modes on a monolithic III-nitride optoelectronic chip Reviewed

Zhang, H; Ye, ZQ; Yan, JB; Shi, F; Shi, ZM; Li, DB; Liu, YH; Amano, H; Wang, YJ

OPTICS LETTERS Vol. 48 ( 19 ) page： 5069 - 5072 2023.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Optics Letters

III-nitride optoelectronic chips have tremendous potential for developing integrated computing and communication systems with low power consumption. The monolithic, top–down approaches are advantageous for simplifying the fabrication process and reducing the corresponding manufacturing cost. Herein, an ultraviolet optical interconnection system is investigated to discover the way of multiplexing between emission and absorption modulations on a monolithic optoelectronic chip. All on-chip components, the transmitter, monitor, waveguide, modulator, and receiver, share the same quantum well structure. As an example, two bias-controlled modulation modes are used to modulate video and audio signals in the experiment presented in this Letter. The results show that our on-chip optoelectronic system works efficiently in the near ultraviolet band, revealing the potential breadth of GaN optoelectronic integration.

DOI： 10.1364/OL.503429

Dislocation Suppresses Sidewall-Surface Recombination of Micro-LEDs Reviewed

Park, JH; Pristovsek, M; Cai, WT; Cheong, HJ; Kang, CM; Lee, DS; Seong, TY; Amano, H

LASER & PHOTONICS REVIEWS Vol. 17 ( 10 ) 2023.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Laser and Photonics Reviews

Nonradiative recombination rate that consists of dislocation-related nonradiative recombination rate (A0) and surface recombination rate (As) is one of the major parameters determining the performance of microlight-emitting diodes (µLEDs). Recent demonstrations improving the efficiency of blue InGaN or red AlGaInP µLEDs using specific methods such as atomic layer deposition or chemical treatment confirm the suppression of As. However, it is hardly found that those methods effectively improve the efficiency of red InGaN µLEDs so far. Here, it is discovered that the dislocation leads to an ineffective As. First, an intrinsic As degrades the external quantum efficiency (EQE) of blue InGaN µLEDs, resulting in EQE decreases with shrinking size. Second, panchromatic cathodoluminescence finds evidence that most of the carriers can be trapped before reaching the sidewall due to high A0. This results in shortened diffusion length of carriers and reduces the number of carriers reaching the sidewall. Consequently, the opposite trend of increasing EQE with shrinking size occurs in the case of red InGaN µLEDs due to an ineffective As. Furthermore, an 8.3 nm quantum well of InGaN with 13% Indium content that can reach a ≈690 nm wavelength at the low current is shown.

DOI： 10.1002/lpor.202300199

UV/DUV light emitters Reviewed

Khan, A; Kneissl, M; Amano, H

APPLIED PHYSICS LETTERS Vol. 123 ( 12 ) 2023.9

Impact of graphene state on the orientation of III-nitride Reviewed

Park, JH; Hu, N; Park, MD; Wang, J; Yang, X; Lee, DS; Amano, H; Pristovsek, M

APPLIED PHYSICS LETTERS Vol. 123 ( 12 ) 2023.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

We attempted to grow (10-13) semi-polar GaN on graphene to confirm the possibility of a remote epitaxy of semi-polar GaN. Single crystalline (10-13) GaN was obtained on an optimized template using optimized growth conditions. However, (10-13), (0002), and other GaN orientations were found under the same growth conditions on a graphene-coated template. Scanning transmission electron microscopy and energy-dispersive x-ray spectroscopy revealed that multi-domain GaN and (0002) GaN occurred in areas with a damaged graphene interfacial layer and intact graphene, respectively. Raman spectroscopy confirmed that graphene could survive under the growth conditions used here. Using cross-sectional scanning electron microscopy, we propose a simple approach to distinguish damaged graphene. Although the remote epitaxy of semi-polar GaN has not been demonstrated despite the usage of an optimized template and growth conditions, our results confirm the importance of the interfacial state in determining the crystallinity of the overgrown layer.

DOI： 10.1063/5.0157588

Investigation of Electrical Properties of N-Polar AlGaN/AlN Heterostructure Field-Effect Transistors Reviewed

Inahara, D; Matsuda, S; Matsumura, W; Okuno, R; Hanasaku, K; Kowaki, T; Miyamoto, M; Yao, YZ; Ishikawa, Y; Tanaka, A; Honda, Y; Nitta, S; Amano, H; Kurai, S; Okada, N; Yamada, Y

PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE Vol. 220 ( 16 ) 2023.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Physica Status Solidi (A) Applications and Materials Science

AlN-based field-effect transistors (FETs) enable high-breakdown voltage, high drain current, and high-temperature operation. To realize high-frequency devices, N-polar AlGaN/AlN heterostructure FETs are focused on. N-polar Al0.1Ga0.9N/Al0.9Ga0.1N/AlN FET is fabricated using metal–organic vapor-phase epitaxy, and its electrical characteristics are evaluated. An N-polar AlN layer is grown on a sapphire substrate with a misorientation angle of 2.0° toward m-axis, on which a 20 nm thick Al0.9Ga0.1N base layer and a 20 nm Al0.1Ga0.9N channel layer are grown. The static FET operation is confirmed to exhibit an n-channel and pinch-off. Normally, during operation with a turn-on voltage of −3.2 V, a high operating breakdown voltage of 620 V and high operating temperature of 280 °C are also confirmed.

DOI： 10.1002/pssa.202200871

Inactivation characteristics of a 280 nm Deep-UV irradiation dose on aerosolized SARS-CoV-2 Reviewed

Takamure, K; Iwatani, Y; Amano, H; Yagi, T; Uchiyama, T

ENVIRONMENT INTERNATIONAL Vol. 177 page： 108022 2023.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Environment International

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 inside the inactivation unit. The RNA concentration of SARS-CoV-2 remained constant when the total irradiation dose of DUV irradiation to the virus exceeded 16.5 mJ/cm2. This observation suggests that RNA damage may occur in regions below the detection threshold of RT-qPCR assay. However, when the total irradiation dose was less than 16.5 mJ/cm2, the RNA concentration monotonically increased with a decreasing LED irradiation dose. However, the nucleocapsid protein concentration of SARS-CoV-2 was not predominantly dependent on the LED irradiation dose. The plaque assay showed that 99.16% of the virus was inactivated at 8.1 mJ/cm2 of irradiation, and no virus was detected at 12.2 mJ/cm2 of irradiation, resulting in a 99.89% virus inactivation rate. Thus, an irradiation dose of 23% of the maximal irradiation capacity of the virus inactivation unit can activate more than 99% of SARS-CoV-2. These findings are expected to enhance versatility in various applications. The downsizing achieved in our study renders the technology apt for installation in narrow spaces, while the enhanced flowrates establish its viability for implementation in larger facilities.

DOI： 10.1016/j.envint.2023.108022

Stress relaxation of AlGaN on nonpolar m-plane GaN substrate Reviewed

Lin, YY; Sena, H; Frentrup, M; Pristovsek, M; Honda, Y; Amano, H

JOURNAL OF APPLIED PHYSICS Vol. 133 ( 22 ) 2023.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Applied Physics

The stress relaxation with increasing thickness of metal-organic vapor phase epitaxy grown Al0.19Ga0.81N on quasi-bulk (101 ¯0) m-plane GaN substrates was investigated by x-ray diffraction. The anisotropic in-plane stress leads to an orthorhombic distortion of the lattice, which requires special mathematical treatment. Extending earlier works, we developed a method to calculate the distortion along [12 ¯10], [0001], and [101 ¯0] and obtained the lattice parameters, Al content, and strain values. The stress relaxation along the two in-plane directions involves two different mechanisms. First, the stress along [12 ¯10] relaxes by the onset of misfit dislocations through the { 10 1 ¯ 0 } ⟨ 1 2 ¯ 10 ⟩ slip system while for thicker layers the stress along [0001] relaxes by crack formation. Comparing the cathodoluminescence emission at room temperature with the expected bandgap showed that both tensile in-plane strains along [12 ¯10] and [0001] decrease the bandgap.

DOI： 10.1063/5.0149838

Impact of Sidewall Conditions on Internal Quantum Efficiency and Light Extraction Efficiency of Micro-LEDs Reviewed

Park, JH; Pristovsek, M; Cai, WT; Cheong, HJ; Tanaka, A; Furusawa, Y; Han, DP; Seong, TY; Amano, H

ADVANCED OPTICAL MATERIALS Vol. 11 ( 10 ) 2023.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Advanced Optical Materials

The sidewall condition is a key factor determining the performance of micro-light emitting diodes (µLEDs). In this study, equilateral triangular III-nitride blue µLEDs are prepared with exclusively m-plane sidewall surfaces to confirm the impact of sidewall conditions. It is found that inductively coupled plasma-reactive ion etching (ICP-RIE) causes surface damages to the sidewall and results in rough surface morphology. As confirmed by time-resolved photoluminescence (TRPL) and X-ray photoemission spectroscopy (XPS), tetramethylammonium hydroxide (TMAH) eliminates the etching damage and flattens the sidewall surface. After ICP-RIE, 100 µm2-µLEDs yield higher external quantum efficiency (EQE) than 400 µm2-µLEDs. However, after TMAH treatment, the peak EQE of 400 µm2-µLEDs increases by ≈10% in the low current regime, whereas that of 100 µm2-µLEDs slightly decreases by ≈3%. The EQE of the 100 µm2-µLEDs decreases after TMAH treatment although the internal quantum efficiency (IQE) increases. Further, the IQE of the 100 µm2-µLEDs before and after TMAH treatment is insignificant at temperatures below 150 K, above which it becomes considerable. Based on PL, XPS, scanning transmission electron microscopy, and scanning electron microscopy results, mechanisms for the size dependence of the EQE of µLEDs are explained in terms of non-radiative recombination rate and light extraction.

DOI： 10.1002/adom.202203128

Lateral p-type GaN Schottky barrier diode with annealed Mg ohmic contact layer demonstrating ideal current-voltage characteristic Reviewed

Lu, S; Deki, M; Kumabe, T; Wang, J; Ohnishi, K; Watanabe, H; Nitta, S; Honda, Y; Amano, H

APPLIED PHYSICS LETTERS Vol. 122 ( 14 ) 2023.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

We have demonstrated the fabrication process for a lateral p-type Schottky barrier diode (SBD) with the annealed Mg ohmic contact layer on a MOVPE-grown p-GaN wafer and measured the electrical characteristic of the diode. Because of the selective-area ohmic contact, the interface between the Schottky electrode and p-type GaN is well protected from any damage introduced by dry-etching or regrowth. The ideality factor of the forward current-voltage characteristic is as low as 1.09 at room temperature and an on-off ratio above 109 is also achieved. Various metals are deposited as the Schottky electrode and the work function dependence of the Schottky barrier height is confirmed with a pinning factor of 0.58. The temperature dependence of the current-voltage characteristic indicates that the GaN p-type SBD still fits the thermionic emission mode at 600 K with an ideality factor of 1.1. The reverse current of the p-SBD is also studied with the Poole-Frenkel emission model, and the trap energy level in the p-GaN is confirmed.

DOI： 10.1063/5.0146080

Simultaneous light emission and detection of an AlGaInP quantum well diode Reviewed

Ye, ZQ; Zhang, H; Gao, XM; Fu, K; Zeng, HB; Liu, YH; Wang, YJ; Amano, H

AIP ADVANCES Vol. 13 ( 4 ) 2023.4

Language：English Publishing type：Research paper (scientific journal) Publisher：AIP Advances

When a quantum well (QW) diode is biased with a forward voltage and illuminated with an external shorter-wavelength light, the device simultaneously emits and detects light, with the injected current and the induced current mixed inside the wells. Separating these superimposed and dynamic electrical signals is useful for the development of multifunctional displays that can simultaneously transmit and receive light signals. By utilizing the unique overlap between the electroluminescence and detection spectra, we establish a wireless optical communication system using two AlGaInP diodes that have identical QW structures. The communication distance is 25 m, with one diode functioning as the transmitter and the other as the receiver. In particular, at the receiver end, the QW diode demonstrates simultaneous light emission and reception ability, and the mixed signals can be efficiently extracted, suggesting great potential for applications from light communication to advanced displays.

DOI： 10.1063/5.0142093

2D-GaN/AlN Multiple Quantum Disks/Quantum Well Heterostructures for High-Power Electron-Beam Pumped UVC Emitters. Reviewed

Jmerik V, Nechaev D, Semenov A, Evropeitsev E, Shubina T, Toropov A, Yagovkina M, Alekseev P, Borodin B, Orekhova K, Kozlovsky V, Zverev M, Gamov N, Wang T, Wang X, Pristovsek M, Amano H, Ivanov S

Nanomaterials (Basel, Switzerland) Vol. 13 ( 6 ) 2023.3

A Review on the Progress of AlGaN Tunnel Homojunction Deep-Ultraviolet Light-Emitting Diodes Invited Reviewed

Nagata, K; Matsubara, T; Saito, Y; Kataoka, K; Narita, T; Horibuchi, K; Kushimoto, M; Tomai, S; Katsumata, S; Honda, Y; Takeuchi, T; Amano, H

CRYSTALS Vol. 13 ( 3 ) 2023.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Crystals

Conventional deep-ultraviolet (UV) light-emitting diodes (LEDs) based on AlGaN crystals have extremely low light-emission efficiencies due to the absorption in p-type GaN anode contacts. UV-light-transparent anode structures are considered as one of the solutions to increase a light output power. To this end, the present study focuses on developing a transparent AlGaN homoepitaxial tunnel junction (TJ) as the anode of a deep-UV LED. Deep-UV LEDs composed of n+/p+-type AlGaN TJs were fabricated under the growth condition that reduced the carrier compensation in the n+-type AlGaN layers. The developed deep-UV LED achieved an operating voltage of 10.8 V under a direct current (DC) operation of 63 A cm−2, which is one of the lowest values among devices composed of AlGaN tunnel homojunctions. In addition, magnesium zinc oxide (MgZnO)/Al reflective electrodes were fabricated to enhance the output power of the AlGaN homoepitaxial TJ LED. The output power was increased to 57.3 mW under a 63 A cm−2 DC operation, which was 1.7 times higher than that achieved using the conventional Ti/Al electrodes. The combination of the AlGaN-based TJ and MgZnO/Al reflective contact allows further improvement of the light output power. This study confirms that the AlGaN TJ is a promising UV-transmittance structure that can achieve a high light-extraction efficiency.

DOI： 10.3390/cryst13030524

Temperature Field, Flow Field, and Temporal Fluctuations Thereof in Ammonothermal Growth of Bulk GaN-Transition from Dissolution Stage to Growth Stage Conditions. Reviewed

Schimmel S, Tomida D, Ishiguro T, Honda Y, Chichibu SF, Amano H

Materials (Basel, Switzerland) Vol. 16 ( 5 ) 2023.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Materials

With the ammonothermal method, one of the most promising technologies for scalable, cost-effective production of bulk single crystals of the wide bandgap semiconductor GaN is investigated. Specifically, etch-back and growth conditions, as well as the transition from the former to the latter, are studied using a 2D axis symmetrical numerical model. In addition, experimental crystal growth results are analyzed in terms of etch-back and crystal growth rates as a function of vertical seed position. The numerical results of internal process conditions are discussed. Variations along the vertical axis of the autoclave are analyzed using both numerical and experimental data. During the transition from quasi-stable conditions of the dissolution stage (etch-back process) to quasi-stable conditions of the growth stage, significant temperature differences of 20 K to 70 K (depending on vertical position) occur temporarily between the crystals and the surrounding fluid. These lead to maximum rates of seed temperature change of 2.5 K/min to 1.2 K/min depending on vertical position. Based on temperature differences between seeds, fluid, and autoclave wall upon the end of the set temperature inversion process, deposition of GaN is expected to be favored on the bottom seed. The temporarily observed differences between the mean temperature of each crystal and its fluid surrounding diminish about 2 h after reaching constant set temperatures imposed at the outer autoclave wall, whereas approximately quasi-stable conditions are reached about 3 h after reaching constant set temperatures. Short-term fluctuations in temperature are mostly due to fluctuations in velocity magnitude, usually with only minor variations in the flow direction.

DOI： 10.3390/ma16052016

Red emission from InGaN active layer grown on nanoscale InGaN pseudosubstrates Reviewed

Cai, WT; Wang, J; Park, JH; Furusawa, Y; Cheong, HJ; Nitta, S; Honda, Y; Pristovsek, M; Amano, H

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 62 ( 2 ) 2023.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

We demonstrated nanoplatelet In x Ga1−x N pseudosubstrates with In content varying from 0 to 0.3 on low-dislocation-density GaN substrates. These nanoplatelets efficiently relax in-plane strain, thus allowing for the use of a thick active layer to reduce built-in polarization. The 15 nm thick InGaN active layers grown under the same conditions on these nanoplatelets showed a remarkable cathodoluminescence redshift from 460 to 617 nm, suggesting enhanced In incorporation efficiency in InGaN nanoplatelets with higher In content. Moreover, the 617 nm-emitting sample presented an imperceptible blueshift under excitation-power-dependent photoluminescence, indicating a weak polarization field introduced by the high-In-content pseudosubstrates and the thick active layer.

DOI： 10.35848/1347-4065/acb74c

Particle Collection Characteristics of Electrostatic Precipitator with Flat Plate Collection Electrodes

TAKAMURE Kotaro, IWATANI Yasumasa, AMANO Hiroshi, YAGI Tetsuya, UCHIYAMA Tomomi

The Proceedings of Mechanical Engineering Congress, Japan Vol. 2023 ( 0 ) page： S054-05 2023

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

<p>An electrostatic precipitator suitable for the collection of aerosol-sized particles is developed. This device is a two-stage electrostatic precipitator divided into a corona discharge part and a collection electrode part. Positive ion is charged to the virus particles by corona discharge, and the negative pole of the collection electrode installed in the later stage collects these particles. The particle collection performance of the system is investigated when the inlet velocity (inlet flowrate) is varied. As a result, even at the same inlet velocity, the collection rate increased with smaller particle size. Furthermore, the collection efficiency of particles decreased with increasing flow velocity.</p>

DOI： 10.1299/jsmemecj.2023.s054-05

Numerical simulation and validation of carbon incorporation in GaN epitaxial growth by MOVPE method

MUKAIYAMA Yuji, WATANABE Hirotaka, NITTA Shugo, IIZUKA Masaya, AMANO Hiroshi

The Proceedings of The Computational Mechanics Conference Vol. 2023.36 ( 0 ) page： OS-1406 2023

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

<p>One of the crucial challenges in GaN epitaxial growth by metalorganic vapor phase epitaxy (MOVPE) method is the control of carbon (C) incorporation, which affects the resistivity of the individual layer of high-power and high-frequency devices based on GaN. Incorporating C into the GaN epilayer depends on various process parameters, such as growth temperature, pressure, carrier gas, flow rates of source gases, and reactor type. To determine the process parameters that control incorporated C concentration and uniformity, we have developed a novel numerical model for C incorporation into the grown GaN epilayer using MOVPE method. The developed model considers C incorporation through the decomposition of Ga source gas. We have implemented this model in a commercial crystal growth simulator, Virtual Reactor Nitride Edition, developed by STR. This study used experimental data to evaluate the dependence of temperature, growth rate, and V/III ratio of C incorporation predicted by the simulations. These results showed a strong correlation between the C concentration and these parameters, and good agreement with the experimental data.</p>

DOI： 10.1299/jsmecmd.2023.36.os-1406

Metal Stop Laser Drilling for Blind via Holes of GaN-on-GaN Devices Reviewed

Sasaoka C., Ando Y., Takahashi H., Ikarashi N., Amano H.

Physica Status Solidi (A) Applications and Materials Science 2023

Language：English Publishing type：Research paper (scientific journal) Publisher：Physica Status Solidi (A) Applications and Materials Science

The metal stop laser drilling of GaN-on-GaN devices is demonstrated using a UV sub-nanosecond laser as a light source. By monitoring the Bremsstrahlung emission at the drilling point, metal stops with a precision higher than 1 μm are realized for vias with a depth of 100 μm. From in situ laser-induced breakdown spectroscopy measurements, it is shown that endpoint detection is realized with high signal-to-noise ratio owing to the difference in the emission process between the strongly excited semiconductor and the metal. Herein, a through-substrate electrode with a resistance of less than 5 mΩ on GaN-on-GaN high-electron-mobility transistor (HEMT) wafers is demonstrated. The fabrication of through-substrate electrodes by this technique provides a simple process that does not require lithography or other complex processes. This process is expected to be useful in the fabrication of future GaN-on-GaN devices, including very thin GaN-on-GaN HEMTs.

DOI： 10.1002/pssa.202200739

Photoelectron beam technology for SEM imaging with pixel-specific control of irradiation beam current

Nishitani T., Arakawa Y., Noda S., Koizumi A., Sato D., Shikano H., Iijima H., Honda Y., Amano H.

Proceedings of SPIE - The International Society for Optical Engineering Vol. 12496 2023

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of SPIE - The International Society for Optical Engineering

The scanning electron microscope (SEM) with photocathode technology was launched by retrofitting the photocathode electron gun to a commercial-based SEM system. In this SEM system, the excitation laser for photoelectron generation from the photocathode is synchronized to the scanning signal. SEM images were obtained by high-speed modulation of the photoelectron beam current using the photocathode SEM, where the location in the field of view and its irradiation current were arbitrarily selected on a pixel-by-pixel basis (Selective e-Beaming technology). As a demonstration experiment contributing to non-contact electrical inspection, low-voltage SEM imaging of MOS-FET structures in 3D-NAND flash memory was performed using this selective e-beam technology. As a result, changes in the voltage contrast of the drain electrode were observed in response to on/off selective electron beam irradiation to the gate electrode in the MOS-FET structure. As an extension of the selective electron beaming technology, a Yield Controlled e-beaming (YCeB) technology was invented to control the secondary electron yield generated in the entire field of view of the SEM image by feedback control of the laser power irradiating the photocathode to the intensity of each pixel in the SEM image. The YCeB image, in which the laser power intensity corresponding to the probe intensity is modulated so that the secondary electron yield generated in the entire field of view of the SEM image is constant, is a clearer image with less noise than the original SEM image.

DOI： 10.1117/12.2657853

Novel Electron Beam Technology using InGaN Photocathode for High-Throughput Scanning Electron Microscope Imaging

Sato, D; Koizumi, A; Shikano, H; Noda, S; Otsuka, Y; Yasufuku, D; Mori, K; Iijima, H; Nishitani, T; Honda, Y; Amano, H

METROLOGY, INSPECTION, AND PROCESS CONTROL XXXVII Vol. 12496 2023

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of SPIE - The International Society for Optical Engineering

An InGaN photocathode with a negative electron affinity (NEA) surface is suitable for industrial use because of features such as a long quantum efficiency lifetime, availability with a visible laser as an excitation light source, and the presence of a transmission-type structure. The first objective is the development of an InGaN photocathode electron gun that can be mounted on a scanning electron microscope (SEM) and the evaluation of the electron beam size at the emission point, maximum emission current, and transverse energy of the electron beam, which are important factors for realizing a high probe current in the SEM. The second objective is the evaluation of emission current stability, while the third objective is the generation of a pulsed electron beam and multi-electron beam from the InGaN photocathode. The parameters of the electron beam from the photocathode electron gun were an emission beam radius of 1 µm, transverse energy of 44 meV, and an emission current of up to 110 µA. Using a high beam current with low transverse energy from the photocathode, a 13 nA probe current with 10 nm SEM resolution was observed with 15 µA emission. At 15 µA, the continuous electron beam emission for 1300 h was confirmed; at 30 µA, the cycle time between the NEA surface reactivations was confirmed to be 90 h with 0.043% stability. Moreover, a 4.4 ns pulsed e-beam with a 4.7 mA beam current was generated, and a 5 × 5 multielectron beam with 12% uniformity was then obtained. The advantages of the InGaN photocathode, such as high electron beam current, low transverse energy, long quantum efficiency lifetime, pulsed electron beam, and multi-electron beam, are useful in industries including semiconductor device inspection tools.

DOI： 10.1117/12.2657032

Development in AlGaN homojunction tunnel junction deep UV LEDs

Nagata K., Anada S., Saito Y., Kushimoto M., Honda Y., Takeuchi T., Amano H.

Proceedings of SPIE - The International Society for Optical Engineering Vol. 12441 2023

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of SPIE - The International Society for Optical Engineering

To reduce the operating voltage, we analyzed the p-n junction of an aluminum gallium nitride (AlGaN) homojunction tunnel junction (TJ) deep-ultraviolet light-emitting diode using phase-shifting electron holography. We obtained a phase image reflecting the band alignment of the p-n homojunction and derived a depletion layer width of approximately 10 nm. We found the AlGaN homojunction TJ forms a p-n junction. Furthermore, the operating voltage reached 8.8 V at 63 A cm-2 by optimizing the structural characteristics of the AlGaN TJ, such as the thickness and impurity concentration, where the thickness of the TJ was 23 nm. We found that the TJ thickness should be at least the same as the depletion layer width at the AlGaN TJ.

DOI： 10.1117/12.2646757

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