Article
Materials Science, Multidisciplinary
Wentao Tian, Mengran Liu, Shuti Li, Chao Liu
Summary: In this study, a hole accelerator structure is proposed to improve the optical power and efficiency of AlGaN-based DUV LEDs by analyzing and enhancing the hole injection efficiency. The results provide possibilities for high-power and high-efficiency applications.
OPTICAL MATERIALS EXPRESS
(2023)
Article
Physics, Applied
Zeyuan Qian, Shijie Zhu, Xinyi Shan, Pan Yin, Zexing Yuan, Pengjiang Qiu, Zhou Wang, Xugao Cui, Pengfei Tian
Summary: This study found that AlGaN-based small-sized UV-C micro-LEDs have higher external quantum efficiency (EQE). Simulations showed that the higher EQE comes from better current spreading and higher light extraction efficiency (LEE) due to a larger proportion of sidewall. The use of small-sized UV-C micro-LEDs effectively addresses the current density non-uniformity and LEE loss issues in UV-C devices.
JOURNAL OF PHYSICS D-APPLIED PHYSICS
(2022)
Article
Physics, Applied
Hirotsugu Kobayashi, Kosuke Sato, Yusuke Okuaki, TaeGi Lee, Tomohiro Morishita, Hiromasa Goto, Naohiro Kuze
Summary: We developed sub-230-nm light emitting diodes (LEDs) with high output power and long lifetime. These LEDs were fabricated on a single-crystal AlN substrate and demonstrated over 1-mW output power under 100-mA operation. The forward voltage was low and the wall plug efficiency was high for these sub-230-nm LEDs.
APPLIED PHYSICS LETTERS
(2023)
Review
Chemistry, Multidisciplinary
Mudassar Maraj, Li Min, Wenhong Sun
Summary: This article summarizes the degradation factors of AlGaN-based near UV-LEDs emitting in the range of 200-350 nm by means of combined optical and electrical characterization, providing theoretical support and guidance for addressing the issue of disinfecting the environment from SARS-CoV-2.
Article
Physics, Applied
Masafumi Jo, Yuri Itokazu, Hideki Hirayama
Summary: In this study, AlGaN LEDs emitting <230 nm UV light were fabricated on sapphire substrates. By employing an extremely thin barrier quantum well and modifying the Al composition of the spacer layer, the emission efficiency and output power of the LED were significantly improved.
APPLIED PHYSICS LETTERS
(2022)
Article
Materials Science, Multidisciplinary
Wentao Tian, Mengran Liu, Shuti Li, Chao Liu
Summary: In this study, a thin AlGaN insertion layer was introduced between the AlGaN electron blocking layer (EBL) and p-AlGaN hole supplier to enhance the hole injection efficiency of DUV LEDs by regulating the energy band at the p-EBL/p-AlGaN interface. It was found that the insertion layer with an Al composition of 45% effectively improved the EQE of DUV LEDs by 40.5% and reduced efficiency droop by 65.5%. This design strategy provides an effective approach to enhance the hole injection efficiency for AlGaN-based DUV LEDs.
OPTICAL MATERIALS EXPRESS
(2023)
Article
Physics, Applied
Ryota Ishii, Akira Yoshikawa, Kazuhiro Nagase, Mitsuru Funato, Yoichi Kawakami
Summary: Time-resolved photoluminescence spectroscopy was conducted on 265 nm AlGaN-based LEDs on AlN substrates under an external bias, revealing that the built-in electric field has an opposite sign to the polarization-induced electric field in the quantum-well layers. Additionally, thermionic and tunneling escape processes play a minor role in the non-unity current injection efficiency under low injection (non-droop) conditions at room temperature.
JAPANESE JOURNAL OF APPLIED PHYSICS
(2021)
Article
Engineering, Electrical & Electronic
Zeyuan Qian, Dong Li, Fangchen Hu, Pengjiang Qiu, Chicheng Ma, Chao Shen, Shanduan Zhang, Nan Chi, Xugao Cui, Pengfei Tian
Summary: This study investigates the size effect of UV-C LEDs on the entire communication system, including modulation bandwidth, channel attenuation, optical coupling, and energy efficiency. Smaller UV-C LEDs demonstrate higher data rates and energy efficiency in UV-C communication, attributed to larger optical modulation bandwidth, spectral efficiency, and signal-to-noise ratio at optimal operating currents.
JOURNAL OF LIGHTWAVE TECHNOLOGY
(2022)
Article
Engineering, Chemical
Tien-Yu Wang, Wei-Chih Lai, Syuan-Yu Sie, Sheng-Po Chang, Cheng-Huang Kuo, Jinn-Kong Sheu
Summary: The introduction of p-AlGaN/AlGaN superlattice (SL) hole injection structure can enhance the performance of deep ultraviolet (DUV) light-emitting diodes (LEDs), resulting in reduced forward voltage and improved light output power.
Article
Materials Science, Multidisciplinary
Mengran Liu, Wentao Tian, Chao Liu
Summary: Insufficient hole injection and current nonuniformity caused by the p-AlGaN hole injection layer are addressed by proposing an Al-linearly-decreasing AlGaN PN junction to replace the conventional p-AlGaN HIL with a constant Al component. The proposed structure enhances hole injection efficiency and improves current uniformity by modulating the barrier height and resistance in the p-AlGaN HIL. The DUV LED with the proposed ALD AlGaN PN junction structure achieves enhanced EQE and improved current uniformity, showing promise for high-performance DUV LEDs.
OPTICAL MATERIALS EXPRESS
(2023)
Article
Chemistry, Physical
Megan N. Aardema, George C. McBane, Simon W. North
Summary: The rotational state distribution and vector correlations of the O-2(a (1)delta(g), v = 0) fragments from photodissociation are investigated, showing a shift to higher rotational states with decreasing wavelength and highly suppressed odd rotational state populations. Measurements agree with classical trajectory calculations but with a slightly narrower distribution. Spatial anisotropy decreases with increasing photon energy, and the v-j correlation is consistent with v perpendicular to j.
JOURNAL OF PHYSICAL CHEMISTRY A
(2022)
Article
Engineering, Electrical & Electronic
Pengfei Tian, Xinyi Shan, Shijie Zhu, Enyuan Xie, Jonathan J. D. McKendry, Erdan Gu, Martin D. Dawson
Summary: As a new form of AlGaN-based UV LED, UV micro-LEDs have shown better performance and wider application potential, addressing fundamental issues of UV LEDs and opening up new areas of application.
IEEE JOURNAL OF QUANTUM ELECTRONICS
(2022)
Article
Optics
Chu-Hui Shen, Ren-Long Yang, Hong-Lin Gong, Li -Hong Zhu, Yu -Lin Gao, Guo -Long Chen, Zhong Chen, Yi -Jun Lu
Summary: This study analyzes the degradation of AlGaN-based UVC LEDs under constant temperature and constant current stress for up to 500 hours. The properties and failure mechanisms of UVC LEDs are thoroughly tested and analyzed using two-dimensional thermal distributions, I-V curves, optical powers, and focused ion beam and scanning electron microscope (FIB/SEM). The results show that increased leakage current and stress-induced defects lead to non-radiative recombination and a decrease in optical power during the early stress stage. Additionally, the deterioration of the p-metal's Cr/Al layer causes an increase in temperature and aggravates the optical power in UVC LEDs after 48 hours of stress. The combination of 2D thermal distribution and FIB/SEM provides a fast and visual way to precisely locate and analyze the failure mechanisms of UVC LEDs.
Article
Physics, Applied
Shunya Tanaka, Shohei Teramura, Moe Shimokawa, Kazuki Yamada, Tomoya Omori, Sho Iwayama, Kosuke Sato, Hideto Miyake, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama, Isamu Akasaki
Summary: A room-temperature pulsed oscillation laser diode with a wavelength of 290 nm and a threshold current density of 35 kA cm(-2) was achieved by fabricating a UV-B laser diode on a thick AlGaN film formed on a 1 µm periodic concavo-convex pattern AlN (PCCP-AlN) on a sapphire substrate. The advantage of using the PCCP-AlN method is that it promotes the nucleation of AlGaN crystals, reducing threading dislocation density while suppressing the formation of irregular giant micrometer-sized hillocks and V-shaped pits.
APPLIED PHYSICS EXPRESS
(2021)
Article
Physics, Applied
J. Glaab, J. Ruschel, N. Lobo Ploch, H. K. Cho, F. Mehnke, L. Sulmoni, M. Guttmann, T. Wernicke, M. Weyers, S. Einfeldt, M. Kneissl
Summary: This study investigates the impact of operation parameters, namely current and temperature, on the degradation of AlGaN-based 233 nm far-ultraviolet-C LEDs. The observed effects can be classified into two groups: a rapid reduction in optical power during the initial 100 hours of operation, accompanied by changes in current and hydrogen concentration, and a gradual reduction in optical power that dominates after 100 hours of operation. The reduction in optical power is accelerated by higher stress currents and current densities, while temperature does not significantly affect the reduction.
JOURNAL OF APPLIED PHYSICS
(2022)
Article
Materials Science, Multidisciplinary
Shu An, Yikai Liao, Sangho Shin, Munho Kim
Summary: The study demonstrates a method to fabricate high-performance Ge photodetectors on black Ge surface, achieving significant enhancement in light absorption through reducing reflection and introducing internal gain.
ADVANCED MATERIALS TECHNOLOGIES
(2022)
Article
Chemistry, Multidisciplinary
Zhi-Jun Zhao, Sang-Ho Shin, Sang Yeon Lee, Bongkwon Son, Yikai Liao, Soonhyoung Hwang, Sohee Jeon, Hyeokjoong Kang, Munho Kim, Jun-Ho Jeong
Summary: A novel nanotransfer printing technique based on chemisorption-assisted nanoscale lower melting effect was developed, enabling the fabrication of two- or three-dimensional nanostructures with feature sizes ranging from tens of nanometers up to a 6 in. wafer-scale. The method overcomes the bottleneck encountered by metal-assisted chemical etching and achieves waferscale, uniform, and controllable nanostructures with extremely high aspect ratios. This technique opens up a viable pathway for next-generation, wafer-scale, uniformly ordered, and controllable nanofabrication, leading to significant advances in various applications.
Article
Chemistry, Multidisciplinary
Xuerui Gong, Zhen Qiao, Yikai Liao, Song Zhu, Lei Shi, Munho Kim, Yu-Cheng Chen
Summary: This study developed a biologically programmable laser that can be manipulated by biomolecular activities, and achieved tunable lasing wavelengths by exploiting the swelling properties of enzyme-responsive hydrogel droplets. Inkjet-printed multiwavelength laser encoding and anti-counterfeiting demonstrated high-level security.
ADVANCED MATERIALS
(2022)
Article
Chemistry, Multidisciplinary
Zhen Qiao, Chaoyang Gong, Yikai Liao, Chenlu Wang, Kok Ken Chan, Song Zhu, Munho Kim, Yu-Cheng Chen
Summary: The study demonstrates tunable optical vortices through the fusion of optofluidics and vortex beams, allowing for fully adjustable and dynamically controlled handedness, topological charges, and lasing wavelengths. Control of topological charges is achieved by tuning the lengths of nanogroove structures, while a wide spectral band of vortex laser beams is realized by alternating different liquid gain materials. Real-time dynamic switching of vortex laser wavelengths is achieved through an optofluidic vortex microlaser device, providing a flexible approach for on-chip vortex sources with high tunability and reconfigurability.
Article
Materials Science, Multidisciplinary
Shu An, Yi-Chiau Huang, Chen-Ying Wu, Po-Rei Huang, Guo-En Chang, Junyu Lai, Jung-Hun Seo, Munho Kim
Summary: GeSn/Si heterojunction photodiodes can be realized by transferring Si nanomembranes onto GeSn/Ge/Si substrates, which extends the wavelength range of light detection. This technique offers low dark current density and high responsivity.
ADVANCED MATERIALS TECHNOLOGIES
(2023)
Review
Materials Science, Multidisciplinary
Shu An, HyunJung Park, Munho Kim
Summary: Flexible optoelectronics have gained significant attention for their potential in healthcare and wearable devices. Narrow bandgap semiconductor nanomembranes (NMs) show promise for flexible near-infrared applications due to their light weight, bendability, and excellent material properties. This review provides a comprehensive summary of recent advances in NBG semiconductor NMs, including their growth, fabrication, characterization, and applications in flexible optoelectronics.
JOURNAL OF MATERIALS CHEMISTRY C
(2023)
Article
Nanoscience & Nanotechnology
Yikai Liao, You Jin Kim, Junyu Lai, Jung-Hun Seo, Munho Kim
Summary: Metal-assisted chemical etching (MacEtch) can create GaN nanoridge surfaces on undoped GaN thin films, reducing surface reflection in the UV regime and enhancing photodiode responsivity by 6 times.
ACS APPLIED MATERIALS & INTERFACES
(2023)
Article
Physics, Applied
Shashwat Rathkanthiwar, Pramod Reddy, Baxter Moody, Cristyan Quinones-Garcia, Pegah Bagheri, Dolar Khachariya, Rafael Dalmau, Seiji Mita, Ronny Kirste, Ramon Collazo, Zlatko Sitar
Summary: High p-conductivity (0.7 S/cm) was achieved in high-Al content AlGaN via Mg doping and compositional grading. A clear transition between the valence band and impurity band conduction mechanisms was observed, which was strongly dependent on the compositional gradient and to some degree on the Mg doping level. A model is proposed to explain the enhancement of conductivity in Mg-doped graded AlGaN films by the polarization field and the transition between the two conduction types. This study opens up a feasible path for achieving technologically useful p-conductivity in AlGaN.
APPLIED PHYSICS LETTERS
(2023)
Article
Chemistry, Multidisciplinary
Ziyihui Wang, Guocheng Fang, Zehang Gao, Yikai Liao, Chaoyang Gong, Munho Kim, Guo-En Chang, Shilun Feng, Tianhua Xu, Tiegen Liu, Yu-Cheng Chen
Summary: Self-propelled micro/nanomotors are used as intelligent sensors for analyzing extracellular biomarkers. A strategy is introduced to amplify subtle signals by coupling strong light-matter interactions on micromotors. A smart whispering-gallery-mode microlaser is demonstrated to analyze extracellular biomarkers in complex environments, providing exclusive molecular labels for cellular profiling of exosomes derived from 3D multicellular cancer spheroids. The proposed autonomous microlaser exhibits promising applications in drug screening, phenotyping, and organ-on-chip applications.
Article
Optics
Zhen Qiao, Zhiyi Yuan, Song Zhu, Chaoyang Gong, Yikai Liao, Xuerui Gong, Munho Kim, Dawei Zhang, Yu-Cheng Chen
Summary: This study presents a strategy to generate OAM microlasers with tunable degree of chirality and large quantum numbers using a ring-structured Fabry-Perot microcavity with nanoscale symmetry-broken geometry. The asymmetry factor of the OAM laser can be continuously tuned by manipulating the optical pump positions. The study also demonstrates high-order OAM lasers with tunable quantum numbers and accomplishes multivortex laser generation on-chip in spatial and temporal domains.
Article
Materials Science, Multidisciplinary
Bongkwon Son, Sang-Ho Shin, Zhi-Jun Zhao, Byeong-Kwon Ju, Jun-Ho Jeong, Munho Kim, Chuan Seng Tan
Summary: Silicon nanowire (NW) array is a promising light-trapping platform due to the strong interaction between light and nanostructure. A systematic study on Si NW array photodetectors with varied NW lengths revealed that photodetectors with 1 μm length provided the highest responsivity of 0.65 A W-1 and a specific detectivity of 1.40 x 10(9) cm Hz(1/2) W-1 at a wavelength of 1000 nm. Furthermore, the introduction of silicon oxide (SiOx) surface passivation improved the responsivity by 13 times at 1100 nm. This study proposes high-efficiency Si NW array photodetectors through NW length control and SiOx surface passivation.
ADVANCED MATERIALS TECHNOLOGIES
(2023)
Article
Chemistry, Multidisciplinary
Yeh-Chen Tai, Shu An, Po-Rei Huang, Yue-Tong Jheng, Kuo-Chih Lee, Hung-Hsiang Cheng, Munho Kim, Guo-En Chang
Summary: For the first time, transfer-printing techniques were used to create a cost-effective, nontoxic GeSn MIR resonant-cavity-enhanced flexible photodetector. By introducing tensile strain, the band structure of the GeSn nanomembrane active layer was effectively modulated, extending the photodetection range in the mid-infrared region and significantly enhancing the optical responsivity.
Article
Materials Science, Multidisciplinary
You Jin Kim, Shu An, Yikai Liao, Po-Rei Huang, Bongkwon Son, Chuan Seng Tan, Guo-En Chang, Munho Kim
Summary: In this study, a new scheme is developed to enhance the responsivity of Ge photodetectors (PDs) by integrating TiN and Ge on flexible platforms. The responsivity is boosted using TiN as a responsivity booster, showing a 63% improvement compared to flat Ge PDs. Moreover, a further increase in responsivity is achieved by applying tensile strain in the active region, reaching a responsivity of 11.5 mA W-1 at 1.55 μm. This work provides an efficient way to enhance the responsivity of flexible Ge PDs via heterogeneous integration of dissimilar materials.
JOURNAL OF MATERIALS CHEMISTRY C
(2023)
Article
Materials Science, Multidisciplinary
Bongkwon Son, Sang-Ho Shin, Yuhao Jin, Yikai Liao, Zhi-Jun Zhao, Jun-Ho Jeong, Qi Jie Wang, Xincai Wang, Chuan Seng Tan, Munho Kim
Summary: In this work, a heavily doped germanium inverted pyramid array is proposed as a candidate for tunable antireflection in the mid-infrared range. The structure consists of inverted pyramid structures formed by metal-assisted chemical etching, with a heavy doping layer obtained through laser annealing. The inverted pyramid acts as an antireflective surface, while the heavy doping layer functions as a high reflector. The reflectance of the inverted pyramid array is observed to be suppressed on undoped Ge and increased after doping, with a consistent reflectance in different wavelength ranges. Doping concentration and depth are identified as important factors for modulating the reflection spectra. The proposed heavily doped inverted Ge pyramid array opens up possibilities for a tunable and metal-oxide-semiconductor-compatible antireflection structure in the mid-infrared range.
JOURNAL OF MATERIALS CHEMISTRY C
(2022)