Low-frequency noise sources in as-prepared and aged GaN-based light-emitting diodes

The low-frequency noise sources are investigated in as-prepared and aged GaN light-emitting diodes (LEDs). Accelerated aging is performed by thermal (300 h at 240 degrees C) and electrical forward-bias stressing (20 and 50 mA for 2500 h). At low currents I < I-RTS, where I-RTS is a critical current, the low-frequency noise is dominated by random telegraph signal (RTS) noise on top of the 1/f noise. An explanation is given for the giant relative current jumps Delta I/I approximate to 50% and an expression for I-RTS is derived. The RTS noise in our devices is a less-sensitive diagnostic tool for studying the results of accelerated aging. Two components of the 1/f noise were observed: one is related to the quantum-well junction and the other is due to series resistance noise. The two 1/f spectra have different current dependences. It was found that the junction 1/f noise is not significantly affected by aging. However, a strong increase in series resistance noise, by a factor of 60-800 compared to unstressed devices, is observed after strong electrical and thermal aging. This high increase goes hand in hand with a relatively small increase in the value of the series resistance (13%-90%). This makes 1/f noise a very sensitive reliability indicator for GaN LEDs after accelerated aging. We discuss the physical origin of LED degradation. (c) 2005 American Institute of Physics.