A Detail Analysis of Electrical and Optical Fluctuations of Green Light-Emitting Diodes by Correlation Method

Abstract

A detail analysis of electrical and optical fluctuations of large power (1 W) green light-emitting diodes (LEDs) is presented. Special attention was directed to measurement and interpretation of correlation coefficient between electrical and optical fluctuations. The correlation coefficient was measured not only over frequency range from 10 Hz to 20 kHz, but also in every one-octave frequency band by using digital filters. It is shown that correlated part of electrical and optical fluctuations for investigated green LEDs is related with random potential fluctuations of parameters of quantum well due to charge carrier capture by the defects in the active layer, while uncorrelated part of electrical noise is caused by parallel leakage channel which resistance is many times higher than that of p-n junction.

Low-frequency noise characteristics of high-power white LED during long-term aging experiment

“…6 the result of the calculation of quantity d j during the ageing is presented. The cross-correlation method has been fully described earlier in [10,14]. Here, the index j = 1 describes the variance of 1/f fluctuations and j = 2 is the variance of 1/f α fluctuations (the shot noise and the noise of the measuring system are uncorrelated).…”

“…The essential feature of low-frequency noise spectroscopy is that measurements are performed under normal bias conditions near the equilibrium state and are nondestructive [6,7]. Due to this reason, the lowfrequency noise characteristics of GaN-based LEDs are of high interest to scientific community [8][9][10][11][12]. However, there are practically no published investigations on the low-frequency noise characteristics of white LEDs during a long ageing experiment at room temperature and manufacturer permissible forward current.…”

“…This is in contrast to highly accelerated testing techniques [2,13] where usually both high temperature and forward current are degradation accelerating factors. What is more, the analysis of the cross-correlation method helps to determine which part of the cross-correlation coefficient between electrical and optical fluctuations is generated by the lowfrequency fluctuations with 1/f, 1/f α or Lorentzian type spectra and to identify the location of possible noise sources in the structure of LED: active or peripheral layers [10,14]. As a white LED has an additional structural component -the phosphor layer, it also has a role in the device degradation process and could act as a possible optical noise source.…”

Light-Emitting Diode Degradation and Low-Frequency Noise Characteristics

“…Optical and (514) electrical noise signals were processed simultaneously using two identical channels comprised from low noise amplifiers, filter systems, analog digital converter (National Instrument TM PCI 6115 board) [12,13]. Such measurement technique allows us to measure the noise spectra and to calculate correlation between two noise sources.…”

Optical and Electrical Noise Characteristics of Side Emitting LEDs

“…Noise power spectral densities of electrical and optical fluctuations can be decomposed to the statistically independent components of 1/f , 1/f α , Lorentzian type, and shot noise spectra [6]: low-frequency electrical fluctuations are completely correlated with optical fluctuations: contact or electrical noises in passive layers of LED do not cause the emitted light intensity fluctuations, i.e., every spectral component of low-frequency electrical noise can be presented as a sum of correlated and uncorrelated parts…”