Performance and Degradation of Commercial Ultraviolet‐C Light‐Emitting Diodes for Disinfection Purposes

Abstract

Herein, the reliability of commercial ultraviolet‐C (UV‐C) light‐emitting diodes (LEDs) subjected to constant current stress is reported. Electrical, optical, and spectral analyses are carried out on UV‐C LEDs with an emission peak of 275 nm and a nominal optical power of 12 mW at 100 mA. Degradation tests are carried out at the maximum rated current, the double and at three times the maximum. The LED lifetime is found to be inversely proportional to the third power of the stress current density, indicating that the degradation mechanism might be activated by high‐energy electrons arising from Auger–Meitner recombination. Electrical characterization indicates an increase in defect‐related leakage, whereas the spectral analysis identifies a variation in two emission peaks which can be ascribed to a defect density increase in the active region and the p‐gallium nitride (GaN) layer of the LEDs. A final remark comes from the strong dependence of lifetime on operating current: increasing current to lower the number of LEDs in a system is not an optimized strategy. In fact, this has a substantial impact on system lifetime, thus lowering the total number of permitted disinfections.

Defects, performance, and reliability in UVC LEDs

“…The interest towards ultraviolet Light-Emitting Diodes (LEDs) is rapidly increasing [1], thanks to the wide field of applications, including water purification, sterilization, surface curing, monitoring of emissions, and lithography. The UVC spectral range (200-280 nm) is of great interest, and can also be used to inactivate viruses and bacteria, including the SARS-CoV-2 [2,3]. Remarkably, it has been shown that the spectral region between 200 nm and 235 nm is safe for exposure, while at the same time being effective for virus inactivation [4,5].…”

Degradation- and Thermal-Related Changes in Selected Electro-Optical Parameters of High-Power 270–280 nm LEDs

“…LED degradation mechanisms related to electroluminescence reduction are the subject of many scientific studies, most of which concern low-power LEDs or elements outside the UVC range [19]. In recent years, in the scientific literature, several reliability analyses (Table 2) and lifetime estimations [19][20][21][22][23][24][25][26][27] of low-power UVC LEDs were published. A variety of operation conditions were assumed.…”

“…The first mechanism is associated with the complete lack of emission of optical radiation, while the second is associated with its successive loss and from the operational point of view is a significant problem because, despite the actual operation of the system, it leads to a deterioration in the effectiveness of the disinfection process [22]. The gradual degradation of the OP of LED depends on the operating temperature and current density [22,[28][29][30][31][32] and is the fastest during the first 10-200 h of operation, then the process slows down [19,21,[33][34][35][36][37]. According to [22,38], the UVC LED's lifetime is inversely proportional to the third power of the stress current density.…”

“…The gradual degradation of the OP of LED depends on the operating temperature and current density [22,[28][29][30][31][32] and is the fastest during the first 10-200 h of operation, then the process slows down [19,21,[33][34][35][36][37]. According to [22,38], the UVC LED's lifetime is inversely proportional to the third power of the stress current density. A model proposed in [21] reveals that LED lifetime is proportional to its radiative recombination coefficient and inversely proportional to the product of its initial nonradiative recombination coefficient and defect growth interest rate, thus providing explicit dependence of the lifetime on the LED junction temperature and current density.…”

“…Instability of the electrical properties also was observed, which resulted in gradual changes in the turn-on voltage of the devices during long-term operation [34]. Several papers prove that the forward voltage decreases within the first hours of operation and increases over longer operation times [20,22,25,37,42], which was explained by a change in the resistivity of the contacts and AlGaN layers. The generation of stress-induced defects and the increase in nonradiative recombination in the early stress stage also causes an increase in leakage current, which results in a decrease in OP [20,33,39,41,42].…”