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1. 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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2. Heterogeneous integration of superconducting thin films and epitaxial semiconductor heterostructures with lithium niobate

   https://doi.org/10.1088/1361-6463/acd7f9  

   Lienhart, Michelle ; Choquer, Michael ; Nysten, Emeline D. S. ; Weiß, Matthias ; Müller, Kai ; Finley, Jonathan J. ; Moody, Galan ; Krenner, Hubert J. ( June 2023 , Journal of Physics D: Applied Physics)

   We report on scalable heterointegration of superconducting electrodes and epitaxial semiconductor quantum dots (QDs) on strong piezoelectric and optically nonlinear lithium niobate. The implemented processes combine the sputter-deposited thin film superconductor niobium nitride and III–V compound semiconductor membranes onto the host substrate. The superconducting thin film is employed as a zero-resistivity electrode material for a surface acoustic wave resonator with internal quality factors$Q\approx 17000$representing a three-fold enhancement compared to identical devices with normal conducting electrodes. Superconducting operation of$\approx 400\mathrm{M}\mathrm{H}\mathrm{z}$resonators is achieved to temperatures$T>7\mathrm{K}$and electrical radio frequency powers$P_{\mathrm{r}\mathrm{f}}>+9\mathrm{d}\mathrm{B}\mathrm{m}$. Heterogeneously integrated single QDs couple to the resonant phononic field of the surface acoustic wave resonator operated in the superconducting regime. Position and frequency selective coupling mediated by deformation potential coupling is validated using time-integrated and time-resolved optical spectroscopy. Furthermore, acoustoelectric charge state control is achieved in a modified device geometry harnessing large piezoelectric fields inside the resonator. The hybrid QD—surface acoustic wave resonator can be scaled to higher operation frequencies and smaller mode volumes for quantum phase modulation and transduction between photons and phonons via the QD. Finally, the employed materials allow for the realization of other types of optoelectronic devices, including superconducting single photon detectors and integrated photonic and phononic circuits.

    

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3. High-performance nanowire ultraviolet light-emitting diodes with potassium hydroxide and ammonium sulfide surface passivation

   https://doi.org/10.1364/AO.400877  

   Bui, Ha Quoc Thang ; Velpula, Ravi Teja ; Jian, Barsha ; Philip, Moab Rajan ; Tong, Hien Duy ; Lenka, Trupti Rajan ; Nguyen, Hieu Pham Trung ( August 2020 , Applied Optics)

   Potassium hydroxide (KOH) and ammonium sulfide$({\mathrm{N}\mathrm{H}}_4{)}_2{\mathrm{S}}_x$have been used as a surface passivation treatment to improve the electrical and optical performance of AlGaN nanowire ultraviolet (UV) light-emitting diodes (LEDs). Enhancements in photoluminescence at 335 nm (49%), optical output power (65%), and electroluminescence (83%), with respect to the as-grown nanowire LED are recorded for the AlGaN nanowire UV LEDs with surface passivation. These enhancements are attributed to the reduced nonradiative recombination on the nanowire surfaces. This study provides a potential surface passivation approach to produce high-power AlGaN nanowire LEDs operating in the UV spectrum.

    

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4. Anisotropic Etching of InGaN Thin Films with Photoelectrochemical Etching to Form Quantum Dots

   https://doi.org/10.3390/ma16051890  

   Wei, Xiongliang ; Al Muyeed, Syed Ahmed ; Xue, Haotian ; Wierer, Jonathan J. ( March 2023 , Materials)

   Traditional methods for synthesizing InGaN quantum dots (QDs), such as the Stranski-Krastanov growth, often result in QD ensembles with low density and non-uniform size distribution. To overcome these challenges, forming QDs using photoelectrochemical (PEC) etching with coherent light has been developed. Anisotropic etching of InGaN thin films is demonstrated here with PEC etching. InGaN films are etched in dilute H2SO4 and exposed to a pulsed 445 nm laser with a 100 mW/cm2 average power density. Two potentials (0.4 V or 0.9 V) measured with respect to an AgCl|Ag reference electrode are applied during PEC etching, resulting in different QDs. Atomic force microscope images show that while the QD density and sizes are similar for both applied potentials, the heights are more uniform and match the initial InGaN thickness at the lower applied potential. Schrodinger-Poisson simulations show that polarization-induced fields in the thin InGaN layer prevent positively charged carriers (holes) from arriving at the c-plane surface. These fields are mitigated in the less polar planes resulting in high etch selectivity for the different planes. The higher applied potential overcomes the polarization fields and breaks the anisotropic etching.

    

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5. N-polar InGaN/GaN nanowires: overcoming the efficiency cliff of red-emitting micro-LEDs

   https://doi.org/10.1364/PRJ.450465  

   Pandey, A. ; Malhotra, Y. ; Wang, P. ; Sun, K. ; Liu, X. ; Mi, Z. ( March 2022 , Photonics Research)

   A high efficiency, high brightness, and robust micro or sub-microscale red light emitting diode (LED) is an essential, yet missing, component of the emerging virtual reality and future ultrahigh resolution mobile displays. We report, for the first time, to our knowledge, the demonstration of an N-polar InGaN/GaN nanowire sub-microscale LED emitting in the red spectrum that can overcome the efficiency cliff of conventional red-emitting micro-LEDs. We show that the emission wavelengths of N-polar InGaN/GaN nanowires can be progressively shifted from yellow to orange and red, which is difficult to achieve for conventional InGaN quantum wells or Ga-polar nanowires. Significantly, the optical emission intensity can be enhanced by more than one order of magnitude by employing anin situannealing process of the InGaN active region, suggesting significantly reduced defect formation. LEDs with lateral dimensions as small as$\sim 0.75\mathrm{\mu m}$, consisting of approximately five nanowires, were fabricated and characterized, which are the smallest red-emitting LEDs ever reported, to our knowledge. A maximum external quantum efficiency$\sim 1.2\%$was measured, which is comparable to previously reported conventional quantum well micro-LEDs operating in this wavelength range, while our device sizes are nearly three to five orders of magnitude smaller in surface area.

    

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