Impact of operation parameters on the degradation of 233 nm AlGaN-based far-UVC LEDs

Abstract

The impact of the operation parameters current and temperature on the degradation of AlGaN-based 233 nm far-ultraviolet-C LEDs is investigated. The observed effects can be divided into two groups: First, a rapid reduction in the optical power to about 50%-30% of the initial value during the first ∼100 h of operation, which is accompanied by an increase in the current below the diffusion voltage from 0.3 to about 1 μA, and a reduction in the hydrogen concentration in the p-side close to the active region. The second group is represented by a gradual reduction of the optical power, which runs in parallel to the effects in the first group and dominates for operation times ≥100 h. The reduction of the optical power is due to a decrease in the slope of the optical power-current characteristic. All effects are accelerated at increased stress currents and current densities - the reduction in the optical power at low (∼20 mA) and high measuring current (∼80 mA) scales with the current to the power of three. For example, after 250 h of operation, the relative optical power at a measuring current of 20 mA has decreased to about 40% when the LED was operated at a stress current of 20 mA and to <10% for a stress current of 100 mA. Furthermore, temperature has no significant impact on the reduction of the optical power during operation, i.e., the relative optical power reduced to about 25% after 250 h both when the LEDs were operated at 20 °C and when they were operated at 75 °C.