Characterization of degradation process in white light nitride-based LEDs by low-frequency noise

Noise characteristics (optical and electrical fluctuations and cross-correlation factor between two noise signals) of high power nitride-based white light emitting diodes (LEDs) have been investigated for initial samples and after accelerated aging. Different spectrum parts from white LED radiation have been investigated separately. Electrical fluctuations and low frequency optical noise of investigated LEDs distinguish by 1/f^α-type spectrum (above 100 Hz shot noise prevails in optical noise). 1/f^α-type optical and electrical fluctuations are partly correlated. After accelerated aging optical 1/f^α-type noise intensity increased, and cross-correlation factor between blue and red light intensity fluctuation increased, too. Origin of increased 1/f^α-type optical noise is defects in the active layer of investigated white LED, and their increase during aging.