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1. Improving carrier transport in AlGaN deep-ultraviolet light-emitting diodes using a strip-in-a-barrier structure

   https://doi.org/10.1364/AO.394149  

   Velpula, Ravi Teja ; Jain, Barsha ; Bui, Ha Quoc Thang ; Shakiba, Fatemeh Mohammadi ; Jude, Jeffrey ; Tumuna, Moses ; Nguyen, Hoang-Duy ; Lenka, Trupti Ranjan ; Nguyen, Hieu Pham Trung ( June 2020 , Applied Optics)

   This paper reports the illustration of electron blocking layer (EBL)-free AlGaN light-emitting diodes (LEDs) operating in the deep-ultraviolet (DUV) wavelength at$\sim <\#comment/>270\mathrm{n}\mathrm{m}$. In this work, we demonstrated that the integration of an optimized thin undoped AlGaN strip layer in the middle of the last quantum barrier (LQB) could generate enough conduction band barrier height for the effectively reduced electron overflow into the$p\text{-}\mathrm{G}\mathrm{a}\mathrm{N}$region. Moreover, the hole injection into the multi-quantum-well active region is significantly increased due to a large hole accumulation at the interface of the AlGaN strip and the LQB. As a result, the internal quantum efficiency and output power of the proposed LED structure has been enhanced tremendously compared to that of the conventional$p\text{-}\mathrm{t}\mathrm{y}\mathrm{p}\mathrm{e}$EBL-based LED structure.

    

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2. GaN/AlN quantum-disk nanorod 280 nm deep ultraviolet light emitting diodes by molecular beam epitaxy

   https://doi.org/10.1364/OL.45.000121  

   Wei, Tongbo ; Islam, S. M. ; Jahn, Uwe ; Yan, Jianchang ; Lee, Kevin ; Bharadwaj, Shyam ; Ji, Xiaoli ; Wang, Junxi ; Li, Jinmin ; Protasenko, Vladimir ; et al ( December 2019 , Optics Letters)

   We report optically and electrically pumped$\sim <\#comment/>280\mathrm{n}\mathrm{m}$deep ultraviolet (DUV) light emitting diodes (LEDs) with ultra-thin GaN/AlN quantum disks (QDs) inserted into AlGaN nanorods by selective epitaxial regrowth using molecular beam epitaxy. The GaN/AlN QD LED has shown strong DUV emission distribution on the ordered nanorods and high internal quantum efficiency of 81.2%, as a result of strain release and reduced density of threading dislocations revealed by transmission electron microscopy. Nanorod assembly suppresses the lateral guiding mode of light, and light extraction efficiency can be increased from 14.9% for planar DUV LEDs to 49.6% for nanorod DUV LEDs estimated by finite difference time domain simulations. Presented results offer the potential to solve the issue of external quantum efficiency limitation of DUV LED devices.

    

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3. Enhanced hole transport in AlGaN deep ultraviolet light-emitting diodes using a double-sided step graded superlattice electron blocking layer

   https://doi.org/10.1364/JOSAB.399773  

   Jain, Barsha ; Velpula, Ravi Teja ; Velpula, Swetha ; Nguyen, Hoang-Duy ; Nguyen, Hieu Pham Trung ( August 2020 , Journal of the Optical Society of America B)

   In this paper, deep ultraviolet AlGaN light-emitting diodes (LEDs) with a novel double-sided step graded superlattice (DSGS) electron blocking layer (EBL) instead of a conventional EBL have been proposed for$\sim <\#comment/>254\mathrm{n}\mathrm{m}$wavelength emission. The enhanced carrier transport in the DSGS structure results in reduced electron leakage into the$p$-region, improved hole activation and hole injection, and enhanced output power and external quantum efficiency. The calculations show that output power of the DSGS structure is$\sim <\#comment/>3.56$times higher and electron leakage is$\sim <\#comment/>12$times lower, compared to the conventional structure. Moreover, the efficiency droop at 60 mA in the DSGS LED was found to be$\sim <\#comment/>9.1\mathrm{\%<\#comment/>}$, which is$\sim <\#comment/>4.5$times lower than the regular LED structure.

    

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4. High-performance electron-blocking-layer-free deep ultraviolet light-emitting diodes implementing a strip-in-a-barrier structure

   https://doi.org/10.1364/OL.400917  

   Velpula, Ravi Teja ; Jain, Barsha ; Velpula, Swetha ; Nguyen, Hoang-Duy ; Nguyen, Hieu Pham Trung ( September 2020 , Optics Letters)

   In this Letter, the electron-blocking-layer (EBL)-free AlGaN ultraviolet (UV) light-emitting diodes (LEDs) using a strip-in-a-barrier structure have been proposed. The quantum barrier (QB) structures are systematically engineered by integrating a 1 nm intrinsic${\mathrm{A}\mathrm{l}}_x{\mathrm{G}\mathrm{a}}_{(1-<\#comment/>x)}\mathrm{N}$strip into the middle of QBs. The resulted structures exhibit significantly reduced electron leakage and improved hole injection into the active region, thus generating higher carrier radiative recombination. Our study shows that the proposed structure improves radiative recombination by$\sim <\#comment/>220\mathrm{\%<\#comment/>}$, reduces electron leakage by$\sim <\#comment/>11$times, and enhances optical power by$\sim <\#comment/>225\mathrm{\%<\#comment/>}$at 60 mA current injection compared to a conventional AlGaN EBL LED structure. Moreover, the EBL-free strip-in-a-barrier UV LED records the maximum internal quantum efficiency (IQE) of$\sim <\#comment/>61.5\mathrm{\%<\#comment/>}$which is$\sim <\#comment/>72\mathrm{\%<\#comment/>}$higher, and IQE droop is$\sim <\#comment/>12.4\mathrm{\%<\#comment/>}$, which is$\sim <\#comment/>333\mathrm{\%<\#comment/>}$less compared to the conventional AlGaN EBL LED structure at$\sim <\#comment/>284.5\mathrm{n}\mathrm{m}$wavelength. Hence, the proposed EBL-free AlGaN LED is the potential solution to enhance the optical power and produce highly efficient UV emitters.

    

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5. Optical beam steering by using tunable, narrow-linewidth butt-coupled hybrid lasers in a silicon nitride photonics platform

   https://doi.org/10.1364/PRJ.382852  

   Zhu, Yeyu ; Zeng, Siwei ; Zhu, Lin ( February 2020 , Photonics Research)

   Chip-scale, tunable narrow-linewidth hybrid integrated diode lasers based on quantum-dot RSOAs at 1.3 μm are demonstrated through butt-coupling to a silicon nitride photonic integrated circuit. The hybrid laser linewidth is around 85 kHz, and the tuning range is around 47 nm. Then, a fully integrated beam steerer is demonstrated by combining the tunable diode laser with a waveguide surface grating. Our system can provide beam steering of 4.1° in one direction by tuning the wavelength of the hybrid laser. Besides, a wavelength-tunable triple-band hybrid laser system working at$\sim 1$,$\sim 1.3$, and$\sim 1.55\mathrm{\mu m}$bands is demonstrated for wide-angle beam steering in a single chip.

    

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