Effect of quantum well number on the efficiency and degradation of AlGaN-based far-UVC LEDs emitting at 233 nm and 226 nm

The effect of the quantum well (QW) number (nQW) in far ultraviolet-C light emitting diodes (LEDs) on the optical power, external quantum efficiency (EQE) and degradation has been investigated. AlGaN-based multi-QW (MQW) LEDs designed for emission at 233 nm and 226 nm with nQW between 1 and 30 are compared. A positive correlation between the optical power at 200 mA and L70 lifetime for large nQW was observed. For the 233 nm LEDs QW numbers 6 ⩽ nQW ⩽ 15 result in optical powers of 4–5 mW at 200 mA (corresponding to a maximum EQE of 0.47% for nQW = 15) and L70 lifetimes of 9–13 h. For nQW = 30 a reduction of output power and L70 lifetime was found indicating an optimum nQW for 233 nm LEDs. For the 226 nm LEDs a constant optical power of 0.5 mW at 200 mA (corresponding to an EQE of 0.05%) was measured independent of nQW. However, the L70 lifetime continuously increases from 7 h for 3 QWs to 13 h for 18 QWs. The enhanced optical power accompanied by a reduced degradation is attributed to a reduced hole leakage from the MQW into the n-side and reduced local charge carrier density per QW for large nQW.