Random number generation is a fundamental task for modern cryptography, secure communications, and stochastic computing. Quantum random number generators (QRNGs) provide inherently unpredictable data derived from quantum physical processes and therefore offer stronger security guarantees than classical approaches. However, some optical QRNGs rely on blue light-emitting diodes (LEDs), which suffer from reduced spectral matching with commonly used silicon avalanche photodiodes (APDs). This mismatch restricts the achievable signal-to-noise ratio (SNR) and limits the extractable quantum entropy. Here, we demonstrate a spontaneous emission-based QRNG employing a green InGaN LED coupled to a silicon APD. The improved spectral overlap between the emitted light and the APD responsivity results in a significantly higher SNR than with previously reported blue LEDs operating at similar electrical power levels. The measured signal is first filtered with a high-pass filter to suppress low-frequency noise, then randomness is extracted using the SHAKE256 hash function. A detailed statistical and spectral analysis is performed to evaluate the extractable entropy of the generated data. A physically reasonable estimation yields a quantum entropy generation rate of 2.78 Gbit/s. These results establish longer-wavelength nitride-based LEDs as a more suitable entropy source for QRNG systems, using inexpensive and widely available silicon photodiodes.

We successfully fabricated GaN-based red resonant-cavity light-emitting diodes by using two dielectric distributed Bragg reflectors as the top and bottom reflector mirrors. The device exhibited resonant modes up to 673 nm, being the longest emission wavelength ever reported for a GaN-based microcavity device. This achievement establishes spectral overlap between GaN-based light-emitting devices and GaAs-based devices. This work contributes significantly to the development of GaN-based microcavity devices in longer wavelengths.

Chromatic dispersion and optical fibre disturbance, such as temperature and vibration, degrade the high spatial resolution of OFDR, especially in remote interrogation. The proposed compensation technique achieves 40. m from over 30 mm. Additionally, we demonstrate its application for interrogating a remote optical device. (c) 2025 The Author(s)

Using atomic force microscopy (AFM) and scanning near-field optical microscopy (SNOM)-photoluminescence (PL) spectroscopy (SNOM-PL), we study the nanoscopic structural and emission properties of a red InGaN hybrid single quantum well (SQW), consisting of a blue and a red InGaN SQW. AFM images reveal the presence of threading-dislocation (TD)-related V-pits and shallow trench defects. The trench defects are classified into three categories on the basis of their height relative to a flat QW: lowered-, level-, and raised-center trench defects. SNOM-PL images demonstrate that TDs and all types of shallow trench defects exhibit a low emission intensity, indicating that they act as non-radiative recombination centers. Unlike previous studies on low-In content samples, all the trench defects exhibit a low emission intensity in our high-In content sample because of In segregation. Given the correlation of dark emission positions between the blue and red emissions, as well as the lower screw-type TD density at the surface than at the n-GaN layer, screw-type TDs should be one of the triggers in the formation of shallow trench defects. Therefore, to enhance the external quantum efficiency of hybrid InGaN red LEDs, it is crucial to suppress In segregation within shallow trench defects and decrease screw-type TD density.

Distributed acoustic sensing (DAS) using optical fiber cables is expected to have various applications. While dark fibers in the cable can be used for DAS, the installation of dedicated sensors on the cable is also a viable option. This study compares DAS measurements using fibers in/on the optical fiber cable. The results indicate that the dedicated sensing fiber exhibited superior measurement performance in several aspects, while dark fibers are affected by various factors, leading to more complex measurement results.

The carrier dynamics of orange/red LEDs incorporating In-rich In0.35Ga0.65N/GaN double quantum well (DQW) structures are explored. The improved hybrid LED structure incorporates an In-poor In0.2Ga0.8N single quantum well (SQW) alongside DQWs that are characterized by enhanced efficiency compared to the control LED comprises In0.35Ga0.65N/GaN DQWs solely. Advanced structural characterizations reveal a unique periodic V-shaped accumulation of Al around threading dislocations (TDs) in the n-AlGaN layer, providing insights into strain distribution around TDs. Advanced optical analyses unveil distinct carrier dynamics. Temperature- photoluminescence (PL), and time-resolved PL reveal unusual behavior in In-rich InGaN LEDs. Unlike blue In-poor InGaN-based LED, the In-rich orange/red LED exhibited a sharp, step-like energy shift accompanied by an abrupt change in the peak width within the intermediate temperature (160-200 K) range. Cathodoluminescence reveals that, in Hybrid LED, the orange/red emission is consistent around V-pits/trenches, while a significant DQW damage occurs below these defects in Control LED, where AlInGaN is formed, resulting in blue emission. Reduced quantum-confined Stark effect is observed in Hybrid LED, addressing key challenges in long-wavelength nitride emitters. The blue SQW inclusion effectively suppresses non-radiative recombination and serves as an efficient carrier reservoir for the active region, achieving a remarkable internal quantum efficiency (27.9%) for the Hybrid LED.

Optical properties of InGaN/GaN red quantum well(QW) and their microcavities were studied and compared under optical pumping. Incidence of the excitation laser from the p-side was employed for both structures in order to acquire better emission characteristics. The QW structure was grown on sapphire substrate by metalorganic vapor-phase epitaxy(MOVPE) with a blue pre-layer QW. X-ray and scanning transmission electron microscopy(STEM) measurements demonstrate the good crystalline quality. Emissions from both blue and red QWs were observed and demonstrated to be dominated by radiative recombination. For red InGaN microcavity with two dielectric distributed Bragg reflector(DBR) mirrors, a high Q factor of 2355 at the longitudinal mode of 612.3 nm was achieved. Discrete higher-order modes were also clearly observed, being attributed to the lateral confinement on the photons in the microcavity caused by change in the refractive index of the laser-irradiation area because of the increase of carrier density. The Purcell effect accelerates the radiation recombination rate, leading to the fast decay process in the red InGaN microcavity which does exist for QWs only. Compared with the red QW sample, the emission of red microcavities is much purer and more stable. The above results lay a foundation for the realization of InGaN-based red vertical-cavity surface-emitting lasers(VCSELs) in the future. (c) 2025 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

InGaN red micro-LEDs were fabricated with indium tin oxide (ITO) and metal n-electrode designs. Micro-LEDs with ITO electrodes achieved a peak on-wafer external quantum efficiency of 2.1% (at 1.25 A cm ^−2 ) and wall-plug efficiency of 1.7% (at 0.64 A cm ^−2 ), representing 1.6 times and 1.5 times improvements compared to metal-based electrodes. Improved performance was attributed to the transparency of ITO, enabling light extraction, while metal electrodes block emission. Both configurations achieved a low leakage current density (≤ 10 ^–7 A cm ^−2 ) and a high peak emission wavelength around 650 nm. These results represent a strong potential for low-power consumption required/area-limited AR/VR applications.

In state-of-the-art red InGaN light-emitting diodes (LEDs), an InGaN-based blue single quantum well (SQW) is used as an underlying layer to improve the red emission efficiency. However, the role of blue SQW is not fully understood. This study investigates the structural and optical properties of blue InGaN SQW by atomic force microscopy (AFM) and photoluminescence (PL) spectroscopy under scanning near-field optical microscopy (SNOM). The AFM images reveal deep and shallow V-pits, corresponding to screw and mixed threading dislocations (TDs). The SNOM-PL intensity image illustrates that all the V-pits correspond to dark spots. We also observe dark spots not associated with the V-pits; given the correspondence between the dark spot density and the edge TD density estimated via x-ray diffraction measurement, these dark spots likely originate from edge TDs. Unlike previous studies, we find that TDs act as nonradiative recombination centers (NRCs) in recent blue SQW, most likely because of the reduction of point defects by InGaN/GaN superlattices. Edge, screw, and mixed TDs have nearly the same impact on the integrated PL intensity of the blue InGaN SQW. Given the correlation of dark emission positions between the blue and red emissions in hybrid red InGaN LEDs in our prior study, all the TDs should function as NRCs in the red emission. The comparable dark spot density between the blue and red SQW suggests that blue SQW suppresses the generation of NRCs in red SQW.

We present light extraction efficiency (LEE) improvement for InGaN red micro-light emitting diodes (micro-LEDs) of various sizes operating at low current densities. We compared the characteristics of micro-LEDs with indium tin oxide (ITO) transparent p-electrodes with conventional opaque metal p-electrodes. 50 mu m x 50 mu m micro-LEDs with ITO p-electrodes achieved a peak on-wafer external quantum efficiency (EQE) of 2.54% with an emission wavelength of 640 nm at a current density as low as 0.4 A/cm2. This represents a 1.18-fold improvement in peak EQE compared to devices with metal p-electrodes. Light ray tracing simulation confirmed that the ITO p-electrodes exhibit 1.18 times higher light escape than metal-based micro-LEDs, validating the role of enhanced light extraction. These findings provide valuable insights for advancing high-definition display and VR applications.

The use of mu LEDs in self-luminous displays is crucial for the development of high-efficiency displays for virtual space services. For this purpose, a stacked monolithic GaInN-based micro light-eimtting diodes (mu LED) device that emits red, green, and blue (RGB) light is obtained. The RGB layers are connected via tunnel junction (TJ) layers. The pixel density is 330 ppi (35 x 15 mu m(2) of mu LED mesa area corresponding to the emission). The cross-sectional transmission electron microscopy analysis indicates that there is not a significant increase in threading dislocations even after stacking the three RGB active layers and two TJ layers. In addition, the X-ray diffraction reciprocal lattice space mapping shows that all the layers grow almost coherently with respect to the GaN substrate. A detailed evaluation of the resulting device shows that the BT.2020 color gamut coverage reaches a maximum of 71%, and the luminance is sufficiently high for head-mounted display applications. Redshifting of the emission wavelength of the red mu LEDs by increasing the InN mole fraction in the GaInN active layer would likely lead to improvement of the color gamut coverage in future studies.

InGaN red LEDs are the key devices to realize AR and VR displays. We have developed InGaN single-QW red LEDs. The InGaN red LEDs show good I-V characteristics. The built-in voltage was only Vb=2.4 V. The peak wavelength at 2.4 V was 641 nm, therefore, the ratio of the photon energy to eVb was as high as 80%. Even at the 20 mA operation, the necessary forward bias was as low as 2.96 V. The light output power density was as high as 0.87 W/cm2 at 20 mA. Therefore, it shows a high WPE of 2.9% at 20 mA.

Visible light communication (VLC), which utilizes LEDs, promises superior privacy and security and reduced impact on surrounding electronics compared to traditional Wi-Fi. This paper explores the potential of InGaN-based micro-light-emitting diodes (micro-LEDs) in high-speed VLC applications, focusing on yellow-green micro-LEDs with nanoporous distributed Bragg reflector (NP-DBR) and red InGaN micro-LEDs. Yellow-green micro-LEDs achieved a maximum external quantum efficiency (EQE) of 8.7%, bandwidth of 442 MHz, and data rate of 800 Mbit/s, while red micro-LEDs demonstrated an EQE of 5.95%, maximum bandwidth of 424 MHz, and data rate of 800 Mbit/s. The application of four core technologies, including circular devices and electrodes, reduced contact electrode area, atomic layer deposition (ALD) for passivation protection, and multi-chip parallel arrays, enhanced optoelectronic characteristics. This paper also highlights the superior performance of InGaN-based red micro-LEDs with a single quantum well (SQW) structure over double quantum wells (DQWs) for VLC applications. The SQW structure yielded higher maximum EQE, modulation bandwidth, and faster transmission rates, paving the way for the potential of full-color micro-display and high-speed VLC applications.

Herein, a selective passivation of p ‐GaN via hydrogen plasma treatment for InGaN single‐quantum‐well (SQW) red light‐emitting diodes (LEDs) is reported. Insulating regions are formed on the p ‐GaN top surface via hydrogen plasma treatment, suppressing current injection beneath the p ‐pad and along the mesa perimeter to increase light output and mitigate non‐radiative recombination. The fabricated LEDs demonstrate a high on‐wafer light output power density of >88 mW cm −2 , a peak on‐wafer external quantum efficiency of 0.65%, and on‐wafer wall‐plug efficiency of 0.41% with a 645 nm peak emission wavelength at 10 mA (7.2 A cm −2 ) current injection. Further, the temperature dependence of InGaN SQW red LEDs is compared with their AlGaInP counterparts. InGaN SQW red LEDs exhibit a high characteristic temperature of 208 K and a small redshift coefficient of 0.072 nm K −1 at 72 A cm −2 current injection, which are almost 3 and 2 times better than the characteristics of AlGaInP red LEDs, respectively.

To investigate nonradiative recombination processes in indium gallium nitride (InGaN)‐based red light‐emitting diodes (LEDs), an InGaN‐based red LED with a hybrid quantum well (QW) structure consisting of red and blue single quantum wells (SQWs) is characterized by micro‐photoluminescence ( μ ‐PL) spectroscopy. The μ ‐PL mapping of the red emission reveals numerous dark spots with various sizes and contrasts. Not only the red and blue (from a blue SQW) but green emission bands are observed at some red dark spots, suggesting that indium (In) segregation is one of the causes of nonradiative recombination in the red emission. Comparing the blue and green emission images to the red emission image reveals that the dark spots in the intensity map of the red emission can be classified into four types. Through this correlative analysis, the red dark spots associated with the dark areas in the intensity map of the blue emission are attributed to the major nonradiative recombination centers in the red emission.