LAUSR

There are numerous applications for deep UV AlGaN light-emitting diodes (LEDs) in virus inactivation, air and water purification, sterilization, bioagent detection, and UV polymer curing. The long-term stability of these LEDs is also of interest for long-duration space missions such as the Laser Interferometer Space Antenna, the first gravitational wave detector in space. We review the literature on long-term aging of these devices as a function of drive current, temperature, and dc versus pulsed operation. LEDs typically show a gradual decline in output power (up to 50%) over extended operating times (>100 h) and the rate of decline is mainly driven by current and temperature. Experimentally, the degradation rate is dependent on the cube of drive current density and exponentially on temperature. The main mechanism for this decline appears to be creation/ migration of point defects. Pre-screening by considering the ratio of band edge-to-midgap emission and LED ideality factor is effective in identifying populations of devices that show long lifetimes (>10,000 hours), defined as output power falling to 70% of the initial value.