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Title: Multi-active region AlGaN UV LEDs with transparent tunnel junctions
Abstract

In this work, we demonstrate two-junction UV LEDs enabled by transparent tunnel junctions. Low voltage-drop tunnel junctions were realized in Al0.3Ga0.7N layers through a combination of high doping and compositional grading. Capacitance and current–voltage measurements confirmed the operation of two junctions in series. The voltage drop of the two-junction LED was 2.1 times that of an equivalent single-junction LED, and the two-junction LED had higher external quantum efficiency (147%) than the single junction.

 
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Award ID(s):
2034140
NSF-PAR ID:
10485266
Author(s) / Creator(s):
; ; ; ; ; ; ;
Publisher / Repository:
DOI PREFIX: 10.35848
Date Published:
Journal Name:
Applied Physics Express
Volume:
16
Issue:
8
ISSN:
1882-0778
Format(s):
Medium: X Size: Article No. 082001
Size(s):
["Article No. 082001"]
Sponsoring Org:
National Science Foundation
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    Abstract

    Connexins form intercellular communication channels, known as gap junctions (GJs), that facilitate diverse physiological roles, from long‐range electrical and chemical coupling to coordinating development and nutrient exchange. GJs formed by different connexin isoforms harbour unique channel properties that have not been fully defined mechanistically. Recent structural studies on Cx46 and Cx50 defined a novel and stable open state and implicated the amino‐terminal (NT) domain as a major contributor for isoform‐specific functional differences between these closely related lens connexins. To better understand these differences, we constructed models corresponding to wildtype Cx50 and Cx46 GJs, NT domain swapped chimeras, and point variants at the 9th residue for comparative molecular dynamics (MD) simulation and electrophysiology studies. All constructs formed functional GJ channels, except the chimeric Cx46‐50NT variant, which correlated with an introduced steric clash and increased dynamical behaviour (instability) of the NT domain observed by MD simulation. Single channel conductance correlated well with free‐energy landscapes predicted by MD, but resulted in a surprisingly greater degree of effect. Additionally, we observed significant effects on transjunctional voltage‐dependent gating (Vjgating) and/or open state dwell times induced by the designed NT domain variants. Together, these studies indicate intra‐ and inter‐subunit interactions involving both hydrophobic and charged residues within the NT domains of Cx46 and Cx50 play important roles in defining GJ open state stability and single channel conductance, and establish the open state Cx46/50 structural models as archetypes for structure–function studies targeted at elucidating GJ channel mechanisms and the molecular basis of cataract‐linked connexin variants.

     
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