Analysis of electrical and optical fluctuations of light-emitting diodes by correlation method

Abstract

A detailed analysis of electrical and optical fluctuations of high power (3 W) light-emitting diodes (LEDs) is presented. A special attention was paid to the measurement and interpretation of simultaneous correlation coefficient between electrical and optical fluctuations. The simultaneous correlation coefficient was measured not only over frequency range from 10 Hz to 20 kHz, but for the first time in every one-octave frequency band. The presented technique not only permitted to determine the correlation coefficient dependence on frequency, but also to estimate what part to correlation coefficient is produced by low-frequency fluctuations with 1/f, 1/f^α and Lorentzian type spectra, respectively. From the obtained experimental and calculation results it is determined that the simultaneous correlated part of electrical and optical fluctuations for these LEDs is related with the defect presence in the active layer or at its interfaces, while the uncorrelated part of electrical noise is caused by parallel leakage channel in other places, and the resistance of this channel is many times higher than that of p–n junction.
Keywords: white light-emitting diodes (LEDs), electrical fluctuations, optical fluctuations, correlation coefficient, correlation in one-octave frequency band
PACS: 72.70.+m, 85.60.Jb