Improved Efficiency of Ultraviolet B Light-Emitting Diodes with Optimized p-Side
phys. stat. sol. (a), vol. 217, no. 20, pp. 2000406 (2020).
Copyright © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
The effects of design and thicknesses of different optically transparent p-current spreading layers [short-period superlattice, superlattice (SL), and bulk p-Al0.38Ga0.62N] as well as the type and thickness of the p-GaN cap layer on the electrical and optical characteristics of 310 nm ultraviolet light-emitting diodes (LEDs) are investigated. Scanning transmission electron microscopy measurements display self-organized composition variations in the nonpseudomorphically grown SLs, reducing the effect of increased hole injection efficiency of a SL. In addition, the effect leads to an increased operation voltage. In contrast, the bulk p-AlGaN layer has a uniform composition and the corresponding LEDs show only a slightly lower output power along with a lower operating voltage. If the thickness of the p-AlGaN bulk layer in the LED is reduced from 150 nm to 50 nm, the output power increases and the operating voltage decreases. Finally, LEDs with a nonuniform p+-GaN cap layer from a 3D island-like growth mode feature the highest output power and operating voltage. In contrast, the output power and operating voltage of LEDs with a smooth and closed cap depend on the thickness of p+-GaN. The highest output power and lowest operating voltage are achieved for LEDs with the thinnest p+-GaN cap.
a Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Strasse 4, 12489 Berlin, Germany
b UVphotonics NT GmbH, Gustav-Kirchhoff-Strasse 4, 12489 Berlin, Germany
c Institute of Physics, Humboldt University of Berlin, Newtonstrasse 15, 12489 Berlin, Germany
light-emitting diode heterostructures, metal-organic vapor phase epitaxies, p-current spreading layers, p-GaN cap layers, ultraviolet light-emitting diodes