Measuring the internal quantum efficiency of light-emitting diodes: towards accurate and reliable room-temperature characterization

Abstract

For accurate and reliable measurement of the internal quantum efficiency (IQE) of light-emitting diodes (LEDs), the method should be theoretically solid and experimentally simple to use without any prior assumption of physical parameters or complicated equipment. In this paper, we critically review the conventional characterization techniques for measuring the IQE of LEDs, including the methods based on temperature-dependent electroluminescence and constant AB(C) models. After reviewing the limitations of the existing IQE measurement techniques, we present the recently proposed method based on the improved AB model, called room-temperature reference-point method (RTRM). The RTRM is then applied to various LED devices to show how the IQE measurement techniques can be utilized to analyze their optoelectronic performances quantitatively.

Intelligent LED Certification System in Mass Production

“…The absolute value of the normalized kurtosis and the normalized skewness is the simplest measure of the non-Gaussianity of the extracted signal. This follows from Equation (19), which minimizes the objective function based on the normalized kurtosis and skewness.…”

“…In view of this, the problem of reconstructing the signal shape can be solved by blind methods for extracting a signal from a mixture of signal and noise. While a whole group of methods and algorithms for blind signal extraction have been developed by now, their direct application does not allow obtaining the highest efficiency of LED [ 18 , 19 ] signal reconstruction. A special algorithm accounting for the statistical properties of signals and noises has to be developed to deal with this issue.…”

Identifying the cause of thermal droop in GaInN-based LEDs by carrier- and thermo-dynamics analysis

“…Despite the recent significant progress, however, AlGaInN-based LEDs still suffer from several efficiency degradations, such as the external quantum efficiency (EQE, η EQE ) gradually degrading with increasing emission wavelength, driving current, and operating temperature, often referred to as “green-gap,” “efficiency droop,” and “thermal droop,” respectively 8 – 10 . Specifically, the thermal droop in GaInN-based blue LEDs has recently become a major research topic because of the continuous demand on white-light emitters that work efficiently in any operating environment 10 – 14 . It is noted that the above three efficiency issues are mainly caused by degradation of the internal quantum efficiency (IQE, η IQE ), as they are not deeply related to degradation of the light-extraction efficiency (LEE, η LEE ) 15 .…”

“…It is noted that the above three efficiency issues are mainly caused by degradation of the internal quantum efficiency (IQE, η IQE ), as they are not deeply related to degradation of the light-extraction efficiency (LEE, η LEE ) 15 . Recall η EQE = η LEE × η IQE 3 , 14 . The thermal droop in GaInN-based blue LEDs can also be explained by the gradual reduction of the IQE with elevating operating temperature.…”

“…Aside from the measurement method issue, equivalent circuits and carrier rate equations are required to decouple τ R and τ NR from the DCL data 21 – 25 . Because the IQE is determined from several complex carrier dynamics in and out of MQWs [recall η IQE = η RE × η IE , where η RE is the radiative efficiency (RE) and η IE is the injection efficiency (IE)] 3 , 14 , it is crucial to adopt the exact equivalent circuit and carrier rate equation that consider all the factors mentioned above comprehensively.…”