Ideality Factor of the Radiative Recombination Current in GaN-Based Light-Emitting Diodes at Cryogenic Temperatures

초록

The ideality factor, an indicator of the dominant recombination mechanism in a diode, is expected to approach unity at low temperatures. This is due to the deactivation of defects as the temperature is decreased. However, experimental data of the GaN-based LED show an unexpected increase in the minimum ideality factor at cryogenic temperatures. It could be suspected that the increased minimum ideality factor might be caused by the increase in series resistance owing to the deactivation of Mg acceptors in p-GaN. In this paper, to understand this phenomenon in GaN-based LEDs more clearly, we examine the radiative ideality factor, which focuses solely on the radiative recombination mechanism, at cryogenic temperatures. The experimental results verify that the radiative ideality factor remains unity from 300 to 100 K, indicating that the increase in the minimum ideality factor is caused by the drastic increase in forward voltage. The high forward voltage at the cryogenic temperature is confirmed to be caused by the space-charge-limited current outside the active region of the GaN-based LED, not simply by the increased series resistance due to the deactivation of Mg acceptors.

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