研究者詳細 - 天野　浩

論文 - 天野　浩

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MOVPE法によるGaNエピタキシャル成長における炭素混入に関する数値解析とその評価 Open Access

向山裕次, 渡邊浩崇, 新田州吾, 飯塚将也, 天野浩

計算力学講演会講演論文集 2023.36 巻 ( 0 ) 頁： OS-1406 2023年

Metal Stop Laser Drilling for Blind via Holes of GaN-on-GaN Devices 査読有り Open Access

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

Physica Status Solidi (A) Applications and Materials Science 2023年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

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 12496 巻 2023年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

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 12496 巻 2023年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

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 12441 巻 2023年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Demonstration of AlN-based Vertical p-n Diodes with Dopant-Free Distributed-Polarization Doping

Kumabe T., Yoshikawa A., Kushimoto M., Honda Y., Arai M., Suda J., Amano H.

Technical Digest - International Electron Devices Meeting, IEDM 2023年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Technical Digest - International Electron Devices Meeting, IEDM

Nearly ideal AlN-based vertical p-n diodes are demonstrated on an AIN substrate utilizing dopant-free distributed-polarization doping (DPD). Capacitance-voltage measurements revealed that the effective doping concentration agreed well with the designed DPD charge concentration. The fabricated devices exhibited a low tum-on voltage of 6.5 V, a low differential specific ON-resistance of 3 mO cm2, and an ideality factor of 2 for a wide range of temperatures (room temperature-573 K). Moreover, the breakdown electric field was 7.3 MV/cm, which was almost twice as high as the reported critical electric field of 4H-SÌC and GaN. These results clearly demonstrate the usefulness of DPD in the fabrication of high-performance AlN-based power devices.

DOI： 10.1109/IEDM45741.2023.10413866

Challenges and opportunities of nitride light emitting devices by HVPE thanks to a stable Mg source

Matsumoto K., Ohnishi K., Amano H.

Proceedings of SPIE - The International Society for Optical Engineering 12441 巻 2023年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Proceedings of SPIE - The International Society for Optical Engineering

Until recently, lack of stable p-type doping source in HVPE hindered its use to the application of III-nitride light emitting devices. Recently, K. Ohnishi discovered the stable MgO source for p-type doping in GaN HVPE. This has enabled the use of HVPE for light emitting devices as well as electron devices such as vertical MOSFET. In this article, we will review the current HVPE technology of p-GaN HVPE, multi-junction AlInGaP/InGaP/GaAs solar cell, InGaN HVPE by tri-chlorides, and discuss the challenge and opportunities of III-nitride HVPE in terms of epitaxial layer design and the remaining issues of the growth of the low temperature buffer, MQWs as well as the source supply design to grow multilayer structures.

DOI： 10.1117/12.2647336

Evaluation of Switching Characteristics of High Breakdown Voltage GaN-PSJ Transistors at Liquid Nitrogen Temperature

Deki M., Kawarabayashi H., Honda Y., Amano H.

AIAA Aviation and Aeronautics Forum and Exposition, AIAA AVIATION Forum 2023 2023年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AIAA Aviation and Aeronautics Forum and Exposition, AIAA AVIATION Forum 2023

We demonstrated static characteristics testing and Double-Pulse-Testing (DPT) at 77 K using GaN-Polarization Super Junction (PSJ) transistors, commercialized GaN HEMTs and commercialized SiC-MOSFETs. In the results of SiC-MOSFETs, total switching losses increased at 77 K due to the increase in on-resistance (Ron). On the other hand, in the results of GaN-PSJ transistors, total switching losses decreased at 77 K due to the increase in channel mobilities. In the case of GaN-PSJ transistors, energy losses which are induced self-charging and discharging (Eqoss) in the upper side DUT increased at 77 K. From the measurement of Vds dependence of Cds, Cds increased at 77 K compared with room temperature conditions. However, total switching losses decreased at low temperatures because Eqoss accounts for about 10% of the switching losses.

DOI： 10.2514/6.2023-4538

GaN substrate cut-out process and GaN on GaN device thinning process with laser slicing Open Access

Tanaka A., Matsushima K., Yui T., Aratani T., Hara K., Kawaguchi D., Watanabe H., Kanemura T., Nagasato Y., Nagaya M., Honda Y., Wakejima A., Ando Y., Onda S., Suda J., Amano H.

Cs Mantech 2023 2023 International Conference on Compound Semiconductor Manufacturing Technology 2023年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Cs Mantech 2023 2023 International Conference on Compound Semiconductor Manufacturing Technology

We have developed a technique to slice GaN substrates with reduced kerf loss and processing time with laser. This technique can also be applied to slicing wafers after device fabrication, allowing a thin device layer to be sliced off from the wafer. This means that the electrical and thermal resistance of the devices can be reduced while the base GaN substrate remains reusable. We believe that the use of both wafer and device processing with laser slicing will greatly reduce the cost of GaN substrates in devices. With this technique, we believe that we can realize the practical application of devices using GaN substrates.

Photon extraction enhancement of praseodymium ions in gallium nitride nanopillars 査読有り Open Access

Sato, SI; Li, S; Greentree, AD; Deki, M; Nishimura, T; Watanabe, H; Nitta, S; Honda, Y; Amano, H; Gibson, BC; Ohshima, T

SCIENTIFIC REPORTS 12 巻 ( 1 ) 頁： 21208 2022年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Scientific Reports

Lanthanoid-doped Gallium Nitride (GaN) integrated into nanophotonic technologies is a promising candidate for room-temperature quantum photon sources for quantum technology applications. We manufactured praseodymium (Pr)-doped GaN nanopillars of varying size, and showed significantly enhanced room-temperature photon extraction efficiency compared to unstructured Pr-doped GaN. Implanted Pr ions in GaN show two main emission peaks at 650.3 nm and 651.8 nm which are attributed to 3P0-3F2 transition in the 4f-shell. The maximum observed enhancement ratio was 23.5 for 200 nm diameter circular pillars, which can be divided into the emitted photon extraction enhancement by a factor of 4.5 and the photon collection enhancement by a factor of 5.2. The enhancement mechanism is explained by the eigenmode resonance inside the nanopillar. Our study provides a pathway for Lanthanoid-doped GaN nano/micro-scale photon emitters and quantum technology applications.

DOI： 10.1038/s41598-022-25522-6

Characteristics of collection and inactivation of virus in air flowing inside a winding conduit equipped with 280 nm deep UV-LEDs Open Access

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

ENVIRONMENT INTERNATIONAL 170 巻頁： 107580 2022年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Environment International

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 the air passing through the conduit with DUV rays. The flow characteristics of air and virus particles inside the virus inactivation unit were investigated using numerical simulations. The air was locally accelerated at the sharp turn parts and flowed along the partition plate in the sharp-turned rectangular conduit. The aerosol particles moving in the sharp-turned rectangular conduit were greatly bent in orbit at the sharp turn parts, and then rapidly approached the partition plate at the lower part of the conduit. Consequently, many particles collided with the partition plates behind the sharp-turn parts. SARS-CoV-2 virus was nebulized in the virus inactivation unit, and the RNA concentration and virus inactivation rate with and without the emission of DUV-LEDs were measured in the experiment. The concentration of SARS-CoV-2 RNA was reduced to 60% through DUV-LED irradiation. In addition, SARS-CoV-2 passing through the virus inactivation unit was inactivated below the detection limit by the emission of DUV-LEDs. The virus inactivation rate and the value of the detection limit corresponded to 99.38% and 35.36 TCID50/mL, respectively.

DOI： 10.1016/j.envint.2022.107580

Scanning electron microscope imaging by selective e-beaming using photoelectron beams from semiconductor photocathodes 査読有り

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

JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B 40 巻 ( 6 ) 2022年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Vacuum Science and Technology B

Pulsed electron beams from a photocathode using an InGaN semiconductor have brought selectively scanning technology to scanning electron microscopes, where the electron beam irradiation intensity and area can be arbitrarily selected within the field of view in SEM images. The p-type InGaN semiconductor crystals grown in the metalorganic chemical vapor deposition equipment were used as the photocathode material for the electron beam source after the surface was activated to a negative electron affinity state in the electron gun under ultrahigh vacuum. The InGaN semiconductor photocathode produced a pulsed electron beam with a rise and fall time of 3 ns, consistent with the time structure of the irradiated pulsed laser used for the optical excitation of electrons. The InGaN photocathode-based electron gun achieved a total beam operation time of 1300 h at 15 μA beam current with a downtime rate of 4% and a current stability of 0.033% after 23 cycles of surface activation and continuous beam operation. The InGaN photocathode-based electron gun has been installed in the conventional scanning electron microscope by replacing the original field emission gun. SEM imaging was performed by selective electron beaming, in which the scanning signal of the SEM system was synchronized with the laser for photocathode excitation to irradiate arbitrary regions in the SEM image at arbitrary intensity. The accuracy of the selection of regions in the SEM image by the selective electron beam was pixel by pixel at the TV scan speed (80 ns/pix, 25 frame/s) of the SEM.

DOI： 10.1116/6.0002111

Miniature optical fiber curvature sensor via integration with GaN optoelectronics Open Access

Shi F., Zhang H., Ye Z., Tang X., Qin F., Yan J., Gao X., Zhu H., Wang Y., Liu Y., Amano H.

Communications Engineering 1 巻 ( 1 ) 2022年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Communications Engineering

Optical fiber curvature sensors have been considered as a promising option for human motion detection due to its good toughness, bending flexibility and anti-electromagnetic interference. However, for wearable devices, the miniature configuration is preferred, and a high integration of the light emitter, receiver and guided fiber is essential to configure the miniaturized sensing system. Here, we present a miniaturized curvature sensing system by integrating a GaN-based optoelectronic chip with the plastical optical fiber (POF). The light emitter and detector are fabricated on a GaN-on-sapphire wafer to form a tiny chip sized at 2.5 × 1.5 mm2. The on-chip photodetector (PD) effectively senses the reflected light intensity, extracting information on the fiber bending deformation. A compact curvature sensing system is demonstrated for finger motion detection with movement angles of 30–90° and frequencies of 0.4, 1, and 1.6 Hz. The results show that the monolithically integrated LED and PD chip can be combined with the POF with reliable operation. The demonstration of the monolithically integrated optoelectronic device suggests a promising potential technology for future wearable fiber optical sensor system.

DOI： 10.1038/s44172-022-00049-w

Key temperature-dependent characteristics of AlGaN-based UV-C laser diode and demonstration of room-temperature continuous-wave lasing 査読有り Open Access

Zhang, ZY; Kushimoto, M; Yoshikawa, A; Aoto, K; Sasaoka, C; Schowalter, LJ; Amano, H

APPLIED PHYSICS LETTERS 121 巻 ( 22 ) 2022年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Physics Letters

Although the pulsed operation of AlGaN-based laser diodes at UV-C wavelengths has been confirmed in the previous studies, continuous oscillation without cooling is difficult because of the high operating voltage. In this study, the temperature dependence of key parameters was investigated and their impact on achieving continuous-wave lasing was discussed. A reduction in the threshold voltage was achieved by tapering the sides of the laser diode mesa and reducing the lateral distance between the n- and p-electrodes. As a result, continuous-wave lasing at room temperature was demonstrated at a threshold current density of 4.2 kA / cm 2 and a threshold voltage of 8.7 V.

DOI： 10.1063/5.0124480

Local stress control to suppress dislocation generation for pseudomorphically grown AlGaN UV-C laser diodes 査読有り Open Access

Kushimoto, M; Zhang, ZY; Yoshikawa, A; Aoto, K; Honda, Y; Sasaoka, C; Schowalter, LJ; Amano, H

APPLIED PHYSICS LETTERS 121 巻 ( 22 ) 2022年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Physics Letters

Previously reported UV-C laser diode (LD) structures have been subject to design constraints owing to dark line defects at the edge of the mesa stripe after device fabrication. To address this issue, a detailed analysis revealed that the dark line defects were dislocations generated by local residual shear stresses associated with mesa formation on highly strained epitaxial layers. A technique for controlling the local concentration of shear stress using a sloped mesa geometry was proposed based on insight gained by modeling the stress distribution at the edge of the mesa stripe. Experimental results showed that this technique succeeded in completely suppressing the emergence of dark-line defects. This technique will be useful in improving the performance of pseudomorphic AlGaN/AlN-based optoelectronic devices, including UV-C LDs.

DOI： 10.1063/5.0124512

Electrical Characteristics of Thermally Stable Ag-Pd-Cu Alloy Schottky Contacts on <i>n-</i>Al<sub>0.6</sub>Ga<sub>0.4</sub>N Open Access

Sim, KB; Kim, SK; Seong, TY; Amano, H

ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY 11 巻 ( 11 ) 2022年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ECS Journal of Solid State Science and Technology

We report the fabrication of high-barrier-height and thermally reliable Schottky contacts to n-Al0.6Ga0.4N by using an Ag-Pd-Cu (APC) alloy. The Schottky barrier heights (SBHs) and ideality factors computed using the current-voltage (I-V) model ranged from 0.82 to 0.97 eV and from 3.15 to 3.44, respectively. The barrier inhomogeneity model and capacitance-voltage (C-V) method yielded higher SBHs (1.62-2.19 eV) than those obtained using the I-V model. The 300 °C-annealed APC sample exhibited more uniform electrical characteristics than the 500 °C-annealed Ni/Au Schottky samples (each with the best Schottky behavior). Furthermore, the scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) results indicated that the APC Schottky contacts were more thermally stable than the Ni/Au contacts. On the basis of the X-ray photoemission spectroscopy (XPS) results, the improved Schottky characteristics of the APC alloy contacts are described and discussed.

DOI： 10.1149/2162-8777/aca1df

Substitutional diffusion of Mg into GaN from GaN/Mg mixture 査読有り Open Access

Itoh, Y; Lu, S; Watanabe, H; Deki, M; Nitta, S; Honda, Y; Tanaka, A; Amano, H

APPLIED PHYSICS EXPRESS 15 巻 ( 11 ) 2022年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Physics Express

We evaluated Mg-diffusion into GaN from GaN/Mg mixture. The diffusion depth of Mg increased with diffusion temperature from 1100 °C to 1300 °C, whereas the Mg concentration remained constant at 2-3 × 1018 cm−3 independent of temperature. The estimated activation energy for Mg diffusion was 2.8 eV, from which the substitutional diffusion mechanism was predicted. Mg-diffused GaN samples showed p-type conductivity with a maximum hole mobility of 27.7 cm2 V−1 s−1, suggesting that substitutional diffusion contributes to Mg activation. This diffusion technique can be used to easily form p-type GaN and has potential as a p-type selective doping technique.

DOI： 10.35848/1882-0786/ac9c83

Adsorption structure deteriorating negative electron affinity under the H<sub>2</sub>O environment 査読有り

Kashima, M; Ishiyama, S; Sato, D; Koizumi, A; Iijima, H; Nishitani, T; Honda, Y; Amano, H; Meguro, T

APPLIED PHYSICS LETTERS 121 巻 ( 18 ) 2022年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Physics Letters

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 prolong the lifetime, it is important to better understand the deterioration of NEA characteristics. The adsorption of residual gases and back-bombardment by ionized residual gases shorten the lifetime. Among the adsorbed residual gases, H2O has a significant influence. However, the adsorption structures produced by the reaction with H2O are not comprehensively studied so far. In this study, we investigated adsorption structures that deteriorated the NEA characteristics by exposing InGaN and GaAs to an H2O environment and discussed the differences in their lifetimes. By comparing the temperature-programmed desorption curves with and without H2O exposure, the generation of CsOH was confirmed. The desorption of CsOH demonstrated different photoemission behaviors between InGaN and GaAs results. InGaN recovered its NEA characteristics, whereas GaAs did not. Considering the Cs desorption spectra, it is difficult for an NEA surface on InGaN to change chemically, whereas that for GaAs changes easily. The chemical reactivity of the NEA surface is different for InGaN and GaAs, which contributes to the duration of photoemission. We have attempted to prolong the lifetime of InGaN by recovering its NEA characteristics. We found that InGaN with NEA characteristics can be reused easily without thermal treatment at high temperatures.

DOI： 10.1063/5.0125344

Monolithic GaN optoelectronic system on a Si substrate 査読有り

Zhang, H; Yan, JB; Ye, ZQ; Shi, F; Piao, JL; Wang, W; Gao, XM; Zhu, HB; Wang, YJ; Liu, YH; Amano, H

APPLIED PHYSICS LETTERS 121 巻 ( 18 ) 2022年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Physics Letters

GaN-based devices have grown rapidly in recent decades, due to their important research value and application prospects. There is a desire to monolithically integrate different GaN devices into a single chip for the development of future optoelectronic systems with low power consumption. In addition to improved multifunctional performance, a miniature integrated system can result in a significant reduction in material costs, processing costs, and packaging costs. In view of such prospects, we propose monolithic, top-down approaches to build III-nitride transmitter, modulator, waveguide, beam splitter, receiver, and monitor as a single unit onto a conventional GaN-on-silicon wafer without involving regrowth or postgrowth doping. Data communication among these components is realized through light propagation, opening up horizons for GaN optoelectronic systems on a chip.

DOI： 10.1063/5.0125324

The photoemission characteristics of a NEA InGaN photocathode by simultaneously supplying Cs and O2 査読有り Open Access

Kashima, M; Itokawa, Y; Kanai, T; Sato, D; Koizumi, A; Iijima, H; Nishitani, T; Honda, Y; Amano, H; Meguro, T

APPLIED SURFACE SCIENCE 599 巻 2022年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Surface Science

A high quantum efficiency (QE) can be obtained on negative electron affinity (NEA) surfaces. It is well-known that NEA surfaces can be formed on semiconductor materials such as GaAs by the alternating supply of cesium (Cs) and oxygen (O2), which is called the yo-yo method. While GaN and related compounds such as InGaN are expected to realize an NEA photocathode with a long lifetime, the surface reactions between GaAs and nitride semiconductors are completely different with respect to the increasing rate of QE induced by the supply of O2. In addition, the surface processes of photoemission from NEA nitride semiconductors have not yet been elucidated. In the present study, a higher QE was achieved in InGaN by simultaneously supplying Cs and O2 instead of using the conventional yo-yo method. The possible Cs adsorption states in relation to the photoemission are also discussed based on the QE tendencies and the temperature programmed desorption (TPD) spectra of the NEA surfaces formed under elevated temperature conditions. This study suggests that the Cs oxide species, which is one of the key compounds for imparting the NEA nature, decomposes at approximately 350 °C and that the InGaN-Cs2O2 structure is a possible candidate for NEA photocathodes.

DOI： 10.1016/j.apsusc.2022.153882

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