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1. Demonstration of 2.71% External Quantum Efficiency at 630 nm in Singular 2 μm Red InGaN Micro‐LEDs on Porous GaN for AR/VR Applications

   https://doi.org/10.1002/adpr.202500264  

   Sanyal, Surjava; Wang, Guangying; Lin, Qinchen; Shih, Timothy; Ghate, Akhilesh; Mukhopadhyay, Swarnav; Gohel, Khush; Shima, Darryl; Balakrishnan, Ganesh; Gupta, Chirag; et al (April 2026, Advanced Photonics Research)

   Next‐generation augmented/virtual reality (AR/VR) headsets require ultrasmall (<5 μm) micro‐LEDs. The III‐Nitride material system is used for highly efficient blue and green devices. Due to the low efficiency of red InGaN LEDs, AlInGaP is used for red emission. However, AlInGaP‐based red micro‐LEDs suffer from intense size‐dependent efficiency reduction. Using topology‐free porous pseudo‐substrates, we fabricated ultra‐small red InGaN micro‐LEDs with a lateral dimension of 2 μm, achieving a peak external quantum efficiency (EQE) of 2.71% at 630 nm under 2.5 A/cm²in an integrating sphere. To the best of our knowledge, this is the highest reported peak EQE for singular (nonarrayed) InGaN micro‐LEDs with a lateral dimension less than 5 μm and a peak wavelength greater than 620 nm. Based on finite‐difference time‐domain simulations, with silicone encapsulation (n = 1.54), the EQE could potentially increase to 4.4%. The peak EQE occurs at a low current density of 2.5 A/cm²and, along with the small device size (2 μm), makes it attractive for AR/VR applications, which require low power consumption and high pixel density. 

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2. Effect of drift layer doping and NiO parameters in achieving 8.9 kV breakdown in 100  μ m diameter and 4 kV/4 A in 1 mm diameter NiO/β-Ga2O3 rectifiers

   https://doi.org/10.1116/6.0002722  

   Li, Jian-Sian; Chiang, Chao-Ching; Xia, Xinyi; Wan, Hsiao-Hsuan; Ren, Fan; Pearton, S. J. (July 2023, Journal of Vacuum Science & Technology A)

   The effect of doping in the drift layer and the thickness and extent of extension beyond the cathode contact of a NiO bilayer in vertical NiO/β-Ga2O3 rectifiers is reported. Decreasing the drift layer doping from 8 × 1015 to 6.7 × 1015 cm−3 produced an increase in reverse breakdown voltage (VB) from 7.7 to 8.9 kV, the highest reported to date for small diameter devices (100 μm). Increasing the bottom NiO layer from 10 to 20 nm did not affect the forward current–voltage characteristics but did reduce reverse leakage current for wider guard rings and reduced the reverse recovery switching time. The NiO extension beyond the cathode metal to form guard rings had only a slight effect (∼5%) in reverse breakdown voltage. The use of NiO to form a pn heterojunction made a huge improvement in VB compared to conventional Schottky rectifiers, where the breakdown voltage was ∼1 kV. The on-state resistance (RON) was increased from 7.1 m Ω cm2 in Schottky rectifiers fabricated on the same wafer to 7.9 m Ω cm2 in heterojunctions. The maximum power figure of merit (VB)2/RON was 10.2 GW cm−2 for the 100 μm NiO/Ga2O3 devices. We also fabricated large area (1 mm2) devices on the same wafer, achieving VB of 4 kV and 4.1 A forward current. The figure-of-merit was 9 GW  cm−2 for these devices. These parameters are the highest reported for large area Ga2O3 rectifiers. Both the small area and large area devices have performance exceeding the unipolar power device performance of both SiC and GaN. 

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3. Advantages of concave quantum barriers in AlGaN deep ultraviolet light-emitting diodes

   https://doi.org/10.1117/12.2650411  

   Jain, Barsha T.; Muthu, Manobalasankar; Velpula, Ravi Teja; Nguyen, Ngoc T.; Nguyen, Hieu Pham (March 2023, Gallium Nitride Materials and Devices XVIII)

   Morkoç, Hadis; Fujioka, Hiroshi; Schwarz, Ulrich T. (Ed.)

   Although AlGaN-based deep ultraviolet (UV) light-emitting diodes (LEDs) have been studied extensively, their quantum efficiency and optical output power still remain extremely low compared to the InGaN-based visible color LEDs. Electron leakage has been identified as one of the most possible reasons for the low internal quantum efficiency (IQE) in AlGaN based UV LEDs. The integration of a p-doped AlGaN electron blocking layer (EBL) or/and increasing the conduction band barrier heights with prompt utilization of higher Al composition quantum barriers (QBs) in the LED could mitigate the electron leakage problem to an extent, but not completely. In this context, we introduce a promising approach to alleviate the electron overflow without using EBL by utilizing graded concave QBs instead of conventional QBs in AlGaN UV LEDs. Overall, the carrier transportation, confinement capability and radiative recombination are significantly improved. As a result, the IQE, and output power of the proposed concave QB LED were enhanced by ~25.4% and ~25.6% compared to the conventional LED for emission at ~254 nm, under 60 mA injection current. 

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4. III-Nitride on-Chip Light Sources for Biological and Medical Applications

   https://doi.org/10.1149/MA2025-01371744mtgabs  

   Zhang, Jing; Boisvere, Jacob; Seitz, Matthew; Smith, Stephanie (July 2025, ECS Meeting Abstracts)

   III-Nitride light-emitting diodes (LEDs) and laser diodes (LDs) are light sources covering ultraviolet (UV) and visible spectral regimes, which offer benefits including compact size, wavelength tuning, long lifetime, and sustainability. UV light sources have a range of applications in the fields of biology and medicine, such as sterilization and the purification of both water and air, where visible light emitters have been used in miniaturized photonic devices for optogenetic applications and other light-based therapies. Those III-Nitride light sources provide tremendous potential to be integrated with silicon (Si)-based lab-on-a-chip (LOC) technology, which typically requires the coupling of an external light source through fiber optic cable, limiting the field deployment of the devices. Integrating an on-chip III-Nitride light source with these devices opens the door to complete LOC technology, allowing for the simultaneous detection of multiple bio agents on a single platform without the need for external photonic sources. While most integrated microsystems still rely on wafer bonding at the device or wafer level, one promising method to achieve the integration of III-nitride UV and visible LEDs and LDs with conventional Si photonics and complementary metal-oxide-semiconductor (CMOS) platforms is through the use of micro-transfer printing (µTP). µTP has greater tolerances in alignment than techniques such as flip-chip integration and allows for the transfer of many devices at once. Additionally, the µTP process does not call for the complex and high temperature processing required for standard wafer bonding or necessitate complicated growth and lattice matching needed for monolithic integration. To enable µTP, an elastomeric, such as polydimethylsiloxane (PDMS), is utilized to create a transfer stamp that is employed for the precise selection of fabricated semiconductor devices for transfer from a source wafer to a target wafer. III-Nitride LEDs or LDs epitaxial structures are grown on a source wafer and fabricated through the creation of tethered coupons, or individual devices. This is accomplished by utilizing III-nitride materials grown on (111) Si. These devices can be fabricated through standard lithography and etching processes, etching down to the (111) Si substrate. A larger mesa can be patterned and etched into the Si substrate, exposing the sidewalls for wet chemical etching. The finished devices are then encapsulated in SiN_xthrough plasma enhanced chemical vapor deposition (PECVD), which is patterned through standard lithography to define tethers and anchors for the subsequent wet etch. The fabricated devices are oriented in such a way as to take advantage of the difference in etch rates (>100x) of Si(110) and Si(111) in potassium hydroxide (KOH), where etching proceeds along the <110> direction. After KOH etching, the devices are left encapsulated in SiN_xand suspended over the silicon substrate with an air gap, while the anchors and tethers are left largely unaffected._{This enables the elastomer stamp to press down, breaking the tethers, and releasing the device. The stamp is then able to transfer the device to a target wafer that has been coated and patterned with InterVia, a spin-on dielectric material that acts as an adhesion layer. The stamp is pressed into the target wafer in such a way that the device is adhered to the target and released from the elastomer stamp. This technique can be applied to LEDs and LDs grown on (111) Si, allowing for the heterogeneous integration of III-nitride LED and LDs with conventional CMOS and Si photonic integrated circuits (PICs) as on-chip light sources, opening the door to complete LOC technology without the need for additional external photonic sources.} 

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5. Improved Performance of Electron Blocking Layer Free AlGaN Deep Ultraviolet Light-Emitting Diodes Using Graded Staircase Barriers

   https://doi.org/10.3390/mi12030334  

   Jain, Barsha; Velpula, Ravi Teja; Patel, Moulik; Sadaf, Sharif Md.; Nguyen, Hieu Pham (March 2021, Micromachines)

   null (Ed.)

   To prevent electron leakage in deep ultraviolet (UV) AlGaN light-emitting diodes (LEDs), Al-rich p-type AlxGa(1−x)N electron blocking layer (EBL) has been utilized. However, the conventional EBL can mitigate the electron overflow only up to some extent and adversely, holes are depleted in the EBL due to the formation of positive sheet polarization charges at the heterointerface of the last quantum barrier (QB)/EBL. Subsequently, the hole injection efficiency of the LED is severely limited. In this regard, we propose an EBL-free AlGaN deep UV LED structure using graded staircase quantum barriers (GSQBs) instead of conventional QBs without affecting the hole injection efficiency. The reported structure exhibits significantly reduced thermal velocity and mean free path of electrons in the active region, thus greatly confines the electrons over there and tremendously decreases the electron leakage into the p-region. Moreover, such specially designed QBs reduce the quantum-confined Stark effect in the active region, thereby improves the electron and hole wavefunctions overlap. As a result, both the internal quantum efficiency and output power of the GSQB structure are ~2.13 times higher than the conventional structure at 60 mA. Importantly, our proposed structure exhibits only ~20.68% efficiency droop during 0–60 mA injection current, which is significantly lower compared to the regular structure. 

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