Low and high frequency noise in LEDs

Abstract

LED degradation is usually associated with defects in the active region. Whereby the noise analysis can be a strong instrument to reveal them. The results of optical noise measurements for commercially available blue LED samples in a wide frequency range from kHz to MHz are reported. Noise spectra were decomposed into components according to the presented theoretical model which includes 1/f-type noise, generation-recombination noise, and white noise. The 1/f$^\gamma$-type noise was modeled as a superposition of generation-recombination noise components at defects with a continuous wide distribution of relaxation lifetimes. The coincidence of the experimental results with 1/f$^\gamma$ model for the low frequency range is proved and a fitting is made. We identified three noise components that are highly current-dependent. The corresponding model of temperature dependence for the low-frequency range was developed. At low currents, the model partially matched the experimental results in the temperature range from 100 K to 300 K at low frequencies. However, high-frequency measurements showed deviations from the expected Lorentzian behavior.