Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the etiologic agent of COVID-19, which has affected the international healthcare systems since the beginning of 2020. Among sanitizing approaches, UV irradiation is a well-known technology often used in different environments to reduce the microbial contamination and the viral transmission. In particular, several works have demonstrated that UVC radiation is able to inactivate SARS-CoV-2 compromising its viral genome and virion integrity. With this work we review and analyze the current status of the pandemic and the state of the art of the UV technology. With traditional UVC discharge lamps having a serious environmental issue, due to their working principle based on mercury, a primary focus is shifted on the aluminum gallium nitride based deep-ultraviolet light emitting diodes. These devices are exploited for compact and environmentally friendly disinfection systems, but efficiency and reliability still play a limiting role into their mass market adoption and system efficacy. In this work we then analyze the latest reports on the effects of dose and wavelength on viral inactivation, thus providing two key pillars for the development of UVC based disinfection systems: the status of the technology and a quantitative evaluation of the dose required to achieve an effective coronavirus inactivation.

In this work, we analyze and model the effect of a constant current stress on an ultraviolet light-emitting diode with a nominal wavelength of 285 nm. By carrying out electrical, optical, spectral, and steady-state photocapacitance (SSPC) analysis during stress, we demonstrate the presence of two different degradation mechanisms. The first one occurs in the first 1000 min of stress, is ascribed to the decrease in the injection efficiency, and is modeled by considering the defect generation dynamics related to the de-hydrogenation of gallium vacancies, according to a system of three differential equations; the second one occurs after 1000 min of stress and is correlated with the generation of mid-gap defects, for which we have found evidence in the SSPC measurements. Specifically, we detected the presence of deep-level states (at 1.6 eV) and mid-gap states (at 2.15 eV), indicating that stress induces the generation of non-radiative recombination centers.

The study of deep-level defects in semiconductors has always played a strategic role in the development of electronic and optoelectronic devices. Deep levels have a strong impact on many of the device properties, including efficiency, stability, and reliability, because they can drive several physical processes. Despite the advancements in crystal growth, wide- and ultrawide-bandgap semiconductors (such as gallium nitride and gallium oxide) are still strongly affected by the formation of defects that, in general, can act as carrier traps or generation-recombination centers (G-R). Conventional techniques used for deep-level analysis in silicon need to be adapted for identifying and characterizing defects in wide-bandgap materials. This topical review paper presents an overview of reviews of the theory of deep levels in semiconductors; in addition, we present a review and original results on the application, limits, and perspectives of two widely adopted common deep-level detection techniques, namely capacitance deep-level transient spectroscopy and deep-level optical spectroscopy, with specific focus on wide-bandgap semiconductors. Finally, the most common traps of GaN and β-Ga₂O₃ are reviewed.

Defects can significantly modify the electro-optical characteristics of InGaN light-emitting diodes (LEDs); however, modeling the impact of defects on the electrical characteristics of LEDs is not straightforward. In this paper, we present an extensive investigation and modeling of the impact of defects on the electrical characteristics of InGaN-based LEDs, as a function of the thickness of the quantum well (QW). First, we demonstrate that the density of defects in the active region of III-N LEDs scales with increasing thickness of the InGaN QW. Since device layers with high indium content tend to incorporate more defects, we ascribed this experimental evidence to the increased volume of defects-rich InGaN associated to thicker InGaN layers. Second, we demonstrate that the current–voltage characteristics of the devices are significantly influenced by the presence of defects, especially in the sub turn-on region. Specifically, we show that the electrical characteristics can be effectively modeled in a wide current range (from pA to mA), by considering the existence of trap-assisted tunneling processes. A good correspondence is obtained between the experimental and simulated electrical characteristics ( I – V ), by using—in the simulation—the actual defect concentrations/activation energies extracted from steady-state photocapacitance, instead of generic fitting parameters.

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.

The aim of this paper is to investigate the degradation mechanisms of UV-B AlGaN-based light-emitting diodes (LEDs) submitted to constant current stress beyond the typical application conditions. We demonstrate the existence of two main degradation mechanisms that significantly impact the relative amplitude of the main quantum well (QW) peak at 310 nm and of a parasitic peak at ~340 nm related to the electron overflow toward the last quantum barrier before the p-side. These mechanisms are thoroughly investigated by means of electrical and optical measurements, and by photocurrent (PC) spectroscopy. We demonstrate that in the first 50 h of stress, degradation is caused by an increased defect density in the last quantum barrier and/or carrier escape from the QWs, which results in a decrease in the QW emission and in an increase in the parasitic peak at 340 nm. For longer stress times, degradation is dominated by a diffusion process, causing an increase in defect density and nonradiative recombination in the LED. This has a direct impact on both the QW peak and the parasitic peak, which show a significant decrease for long stress times. PC spectroscopy demonstrates that the defects responsible for degradation are most likely located next to mid-gap, thus acting as efficient nonradiative recombination centers.