ABSTRACT
In the last year the market of ultraviolet (UV) light-emitting diodes (LEDs) had a huge increase due to the higher demand of devices caused by the pandemic crisis. In fact, it was demonstrated that UV LEDs, and in particular UV-B and UV-C LEDs, could be used as efficient sources for the disinfection of surfaces against Sars-CoV-2. In this work, we investigated electrical, optical and spectral degradation mechanisms in a series of commercial UV-C LEDs (275 nm - 280 nm) available on market. We present an exhaustive comparison of the main sample characteristics, studying their evolution when the LEDs are submitted to constant current stress tests (for about 350 h) at the absolute maximum current indicated in the respective datasheets. In particular, we carried out an extensive set of measurements, including current-voltage (I-V), optical power-current (L-I) and power spectral density (PSD) characteristics at various steps of stress, combined with the analysis of the drive voltage during the tests and of the thermal droop of the devices. We found: (i) a set of LEDs with a promising L80 of 10000 min (about 170 h), (ii) the presence of parasitic peaks and bands in all devices, ascribed to radiative recombination outside the QWs, and (iii) a substantial increase in thermal droop in all LEDs due to a decrease in injection efficiency and an increase in SRH recombination events during the stress tests. © 2022 SPIE. All rights reserved.
ABSTRACT
With this study, we report on the reliability of the most recent commercial UVC LED devices. The current COVID-19 pandemic urged the development of antiviral technologies, and one of the most effective is based on UVC irradiation, which can be effectively achieved by means of Deep UV LEDs. The development of antiviral systems based on UVC LEDs strongly depends on their efficacy and reliability. We propose an in-depth analysis of four different state-of-the-art commercial LEDs suitable for disinfection applications. LEDs have been subjected to a controlled stress test near their application limits, and their reliability and characteristics have been analyzed and studied. Results indicate a still limited reliability, with a degradation possibly related to an increase in Shockley–Read–Hall (SRH) recombination. Finally, some relevant product design suggestions will be proposed based on the results of this work. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
ABSTRACT
The aim of this paper is the definition of a model for the degradation of an AlGaN-based ultraviolet (UV) Light Emitting Diode (LED) with a nominal wavelength of 285 nm (UV-C). These devices are widely used in disinfection, sterilization, water purification, medical devices, in plant lighting and as insect traps;moreover, UV antiviral treatments are being developed recently, under the push of the current COVID-19 emergency. We analyzed the behavior of the devices during a constant current stress at the current of 250 mA, through electrical (I-V), optical (L-I) and spectral (PSD) measurements and steady state photocapacitance (SSPC) analysis. By investigating the optical measurements, we found out the presence of two different degradation mechanisms, one before 1000 min of stress and one after 1000 min of stress. We ascribed the first one to a decrease in the injection efficiency and we modeled it with a system of three differential rate equations to describe the dynamics of the de-hydrogenation of gallium vacancies, that lead to a defects generation. On the other hand, the second degradation mechanism is well correlated to the generation of midgap defects (Ec-2.15 eV), as detected from the SSPC analysis, that indicates the generation of non-radiative centers induced by the stress. © 2021 SPIE.