Initial benchmarks of UV LEDs and Comparisons with White LEDs

Abstract

Light-emitting diodes (LEDs) can emit radiation that spans the range from near infrared (IR) to all three bands of ultraviolet (UV) radiation (i.e., UV-A, UV-B, UV-C). These emission sources are fabricated by varying doping levels of the aluminum gallium indium nitride (AlGaInN) alloy system, which tunes the emission wavelength of the semiconductor. During the past 20 years, the blue LED, made from InGaN, has advanced technologically to the point that it now provides the backbone for the solid-state lighting revolution that is occurring in general illumination. With proper doping, the InGaN alloy system can be extended to UV-A emission wavelengths as low as 362 nanometers (nm); however, producing LEDs that emit in the UV-B and UV-C bands requires the use of AlGaN alloys. Unfortunately, AlGaN semiconductors are not at the same level of technological development as InGaN, and LEDs made from AlGaN suffer from a variety of inefficiencies arising from electrical and optical limitations of the current technology. This report is aimed at benchmarking the performance of UV LEDs across all three bands in an effort to understand the current state of the technology.
UV sources have many industrial applications, and their total market exceeds $750 million. Examples of applications for UV sources include ink and polymer curing (primarily UV-A sources), medical treatments (primarily UV-B sources), and disinfection (primarily UV-C sources). While UV-A applications are the largest market today, the increased need for surface and air disinfection is expected to create a significant market opportunity for UV-C sources in the near future. The current technology most widely used for UV sources in all three bands is the mercury discharge lamp, which has moderate energy efficiency but also has a number of limitations including compatibility with compact form factors, long-term reliability, and end-of-life issues associated with disposing a glass tube containing mercury without creating environmental contamination. UV LEDs have the potential to displace mercury lamps in UV applications in much the same way that white LEDs have displaced fluorescent lamps in many commercial and residential lighting markets.
The primary goal of this report is to benchmark the initial level of performance of a selection of commercial UV LEDs across all three bands (i.e., UV-A, UV-B, UV-C). To provide the initial performance benchmarks, a test matrix containing 13 different UV LED products was created in association with the LED Systems Reliability Consortium (LSRC). The products in this test matrix were all commercially available as of June 2021, and at least 22 samples of each product were tested. In addition, two common, commercial white LEDs were tested to provide a benchmark against blue-pumped white LEDs. Testing of the samples included electrical performance testing (e.g., current-voltage measurements) and photometric testing in a calibrated integrating sphere capable of measuring devices in the UV-A, UV-B, and UV-C bands. The electrical testing provided insights into the performance of the semiconductor layers in the LEDs, allowing parameters such as the threshold voltage (Vth) and serial resistance (Rserial) of each sample to be determined. The photometric testing provided insights into emission wavelengths, peak shapes, and radiant efficiencies for each sample. Combined, the information from these tests permits the overall device efficiencies to be compared and provides insights into the electrical and optical performance of the technology.