AlGaN Microfins as Nonpolar UV Emitters Probed by Time-Resolved Cathodoluminescence

authored by: Hendrik Spende, Christoph Margenfeld, Andreas Waag
Abstract: Despite the continuous technological progress and recent commercialization of UV light emitting diodes for sterilization and disinfection applications, the performance of solid-state UV emitters still lags far behind that of their InGaN-based counterparts, which emit in the visible blue-green spectrum. Both fundamental physical aspects and material quality restrictions have been discussed as origin of this striking difference. In this study, GaN/AlGaN core-shell microfins with a-plane sidewalls are proposed as a model system to demonstrate the efficiency potential of ultra-low-defect nonpolar UV emitters. Such structures are manufactured by bottom-up selective-area metalorganic vapor phase epitaxy of GaN microfin cores and further overgrowth of the AlGaN active region, employing a compositionally graded GaN/AlGaN short-period superlattice for strain management. Using this approach, mostly crack-free AlGaN quantum wells emitting around 321 nm could be realized with a threading dislocation density of as low as (6 ± 3) × 107 cm-2. The carrier dynamics within the nonpolar AlGaN structures are studied by time-resolved cathodoluminescence spectroscopy, revealing fast radiative recombination lifetimes down to 0.6 ns and distinct signatures of carrier localization at low temperatures. Delayed carrier emission from localized states within the cladding is proposed to be a cause for anomalously high effective carrier lifetimes observed at temperatures below 80 K. By analyzing the characteristic temperature dependence of radiative and nonradiative recombination processes and fitting the lifetime data with an appropriate model across the whole temperature range, a room-temperature internal quantum efficiency of (40 ± 6) % is estimated for the studied sample. The findings corroborate the interest in nonpolar AlGaN structures as highly efficient UV emitters.
External Organisation(s): Technische Universität Braunschweig
Type: Article
Journal: ACS PHOTONICS
Volume: 9
Pages: 1594-1604
No. of pages: 11
ISSN: 2330-4022
Publication date: 18.05.2022
Publication status: Published
Peer reviewed: Yes
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Electrical and Electronic Engineering, Biotechnology
Electronic version(s): https://doi.org/10.1021/acsphotonics.1c01794 (Access: Closed)

BibTeX

@article{49c159c5a00e497b9d8a3652e74bc513,
title = "AlGaN Microfins as Nonpolar UV Emitters Probed by Time-Resolved Cathodoluminescence",
abstract = "Despite the continuous technological progress and recent commercialization of UV light emitting diodes for sterilization and disinfection applications, the performance of solid-state UV emitters still lags far behind that of their InGaN-based counterparts, which emit in the visible blue-green spectrum. Both fundamental physical aspects and material quality restrictions have been discussed as origin of this striking difference. In this study, GaN/AlGaN core-shell microfins with a-plane sidewalls are proposed as a model system to demonstrate the efficiency potential of ultra-low-defect nonpolar UV emitters. Such structures are manufactured by bottom-up selective-area metalorganic vapor phase epitaxy of GaN microfin cores and further overgrowth of the AlGaN active region, employing a compositionally graded GaN/AlGaN short-period superlattice for strain management. Using this approach, mostly crack-free AlGaN quantum wells emitting around 321 nm could be realized with a threading dislocation density of as low as (6 ± 3) × 107 cm-2. The carrier dynamics within the nonpolar AlGaN structures are studied by time-resolved cathodoluminescence spectroscopy, revealing fast radiative recombination lifetimes down to 0.6 ns and distinct signatures of carrier localization at low temperatures. Delayed carrier emission from localized states within the cladding is proposed to be a cause for anomalously high effective carrier lifetimes observed at temperatures below 80 K. By analyzing the characteristic temperature dependence of radiative and nonradiative recombination processes and fitting the lifetime data with an appropriate model across the whole temperature range, a room-temperature internal quantum efficiency of (40 ± 6) % is estimated for the studied sample. The findings corroborate the interest in nonpolar AlGaN structures as highly efficient UV emitters.",
keywords = "AlGaN UV LED, cathodoluminescence, IQE, MOVPE, nonpolar quantum well, time-resolved spectroscopy",
author = "Hendrik Spende and Christoph Margenfeld and Andreas Waag",
note = "Funding information: H.S. and C.M. contributed equally to this work. C.M. performed the growth of the microfins and CL characterization, processing of the data, and took active part in the writing this paper. H.S. performed the time-resolved CL measurements, processing of the data, and took active part in the writing this paper. A.W. acquired the funding for this project and supervised this research. All authors contributed to the discussion and writing of the paper.",
year = "2022",
month = may,
day = "18",
doi = "10.1021/acsphotonics.1c01794",
language = "English",
volume = "9",
pages = "1594--1604",
journal = "ACS PHOTONICS",
issn = "2330-4022",
publisher = "American Chemical Society",
number = "5",
}