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1. Numerical investigation on the device performance of electron blocking layer free AlInN nanowire deep ultraviolet light-emitting diodes

   https://doi.org/10.1364/OME.380409  

   Velpula, Ravi Teja ; Jain, Barsha ; Bui, Ha Quoc Thang ; Pham, Tan Thi ; Le, Van Thang ; Nguyen, Hoang-Duy ; Lenka, Trupti Ranjan ; Nguyen, Hieu Pham Trung ( January 2020 , Optical Materials Express)

   We report on the illustration of the first electron blocking layer (EBL) free AlInN nanowire light-emitting diodes (LEDs) operating in the deep ultraviolet (DUV) wavelength region (sub-250 nm). We have systematically analyzed the results using APSYS software and compared with simulated AlGaN nanowire DUV LEDs. From the simulation results, significant efficiency droop was observed in AlGaN based devices, attributed to the significant electron leakage. However, compared to AlGaN nanowire DUV LEDs at similar emission wavelength, the proposed single quantum well (SQW) AlInN based light-emitters offer higher internal quantum efficiency without droop up to current density of 1500 A/cm²and high output optical power. Moreover, we find that transverse magnetic polarized emission is ∼ 5 orders stronger than transverse electric polarized emission at 238 nm wavelength. Further research shows that the performance of the AlInN DUV nanowire LEDs decreases with multiple QWs in the active region due to the presence of the non-uniform carrier distribution in the active region. This study provides important insights on the design of new type of high performance AlInN nanowire DUV LEDs, by replacing currently used AlGaN semiconductors.

    

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2. 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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3. 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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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. Controlled carrier mean free path for the enhanced efficiency of III-nitride deep-ultraviolet light-emitting diodes

   https://doi.org/10.1364/AO.418603  

   Jain, Barsha ; Velpula, Ravi Teja ; Patel, Moulik ; Nguyen, Hieu Pham Trung ( April 2021 , Applied Optics)

   Electron overflow from the active region confines the AlGaN deep-ultraviolet (UV) light-emitting diode (LED) performance. This paper proposes a novel approach to mitigate the electron leakage problem in AlGaN deep-UV LEDs using concave quantum barrier (QB) structures. The proposed QBs suppress the electron leakage by significantly reducing the electron mean free path that improves the electron capturing capability in the active region. Overall, such an engineered structure also enhances the hole injection into the active region, thereby enhancing the radiative recombination in the quantum wells. As a result, our study shows that the proposed structure exhibits an optical power of 9.16 mW at$\sim <\#comment/>284\mathrm{n}\mathrm{m}$wavelength, which is boosted by$\sim <\#comment/>40.5\mathrm{\%<\#comment/>}$compared to conventional AlGaN UV LED operating at 60 mA injection current.

    

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