TY - JOUR

T1 - AlGaN Microfins as Nonpolar UV Emitters Probed by Time-Resolved Cathodoluminescence

AU - Spende, Hendrik

AU - Margenfeld, Christoph

AU - Waag, Andreas

N1 - Publisher Copyright: © 2022 The Authors. Published by American Chemical Society.

PY - 2022/5/18

Y1 - 2022/5/18

N2 - 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.

AB - 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.

KW - AlGaN UV LED

KW - cathodoluminescence

KW - IQE

KW - MOVPE

KW - nonpolar quantum well

KW - time-resolved spectroscopy

UR - http://www.scopus.com/inward/record.url?scp=85129043090&partnerID=8YFLogxK

U2 - 10.1021/acsphotonics.1c01794

DO - 10.1021/acsphotonics.1c01794

M3 - Article

VL - 9

SP - 1594

EP - 1604

JO - ACS PHOTONICS

JF - ACS PHOTONICS

SN - 2330-4022

IS - 5

ER -