LED Internal Quantum Efficiency Measurement via Current-Dependent Light Intensity
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Solution Overview
Problem
Current methods for measuring internal quantum efficiency of light emitting diodes (LEDs) are time-consuming, require expensive equipment, and cannot measure the efficiency of the entire wafer due to size restrictions, with temperature-dependent electroluminescence methods being limited and external quantum efficiency measurements being indirect.
Innovation Solution
A method and device that measure light intensity and calculate relative radiative efficiency, extract a reference injection current to minimize recombination coefficient changes, and calculate internal quantum efficiency in various injection currents, allowing for non-destructive, rapid measurement of internal quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If temperature-dependent electroluminescence method is used to measure internal quantum efficiency, then measurement accuracy can be improved, but measurement time increases significantly (about 5-6 hours) and expensive equipment is required
Solution Approach 1:
The patent changes the measurement parameter from temperature-dependent electroluminescence to current-dependent light intensity measurement. By measuring light intensity at different injection currents and calculating relative radiative efficiency, the method eliminates the need for temperature variation while maintaining measurement accuracy. This resolves the contradiction by finding an alternative parameter (current instead of temperature) that achieves the same measurement goal without the time penalty.
Solution Approach 2:
The patent replaces the complex temperature control system (mechanical/thermal system requiring expensive equipment and long stabilization times) with a simple electrical current control system. By substituting the measurement approach from thermal field to electrical field, the method achieves rapid measurement without expensive temperature test equipment, resolving both the time loss and equipment cost issues while maintaining measurement precision.
2Measurement precision
If temperature test device with small chamber is used, then internal quantum efficiency can be measured, but only a very small portion of wafer can be measured due to size restriction
Solution Approach 1:
The patent replaces the confined thermal measurement environment with an open electrical measurement system. By using current injection and light intensity detection that does not require a small chamber, the method can measure large portions or entire wafers, resolving the contradiction between measurement capability and wafer coverage quantity.
3Productivity
If external quantum efficiency is measured experimentally, then measurement can be performed, but internal quantum efficiency and light extraction efficiency cannot be separately measured
Solution Approach 1:
The patent segments the measurement process into two distinct parts: first measuring external quantum efficiency, then separately measuring light extraction efficiency through specific optical configurations. By dividing the measurement into separable components, the method enables independent determination of internal quantum efficiency and light extraction efficiency, resolving the information loss problem while maintaining measurement efficiency.
Solution Approach 2:
The patent introduces light extraction efficiency as an intermediary measurement parameter. By measuring this intermediate quantity through specific optical setups and using it as a bridge, the method enables calculation of internal quantum efficiency from external quantum efficiency measurements, thus recovering the separated information without sacrificing productivity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables quick (about 5 minutes) and separate measurement of internal quantum efficiency from external quantum efficiency, facilitating defect diagnosis in LEDs, and allowing for efficient production monitoring.
Implementation Method 1
The LED is a kind of p-n junction diode and is a semiconductor device using electroluminescence, in which light is emitted when forward voltage is applied to the semiconductor device.
Data Source
AI summary
A method for measuring the efficiency of an optical element is disclosed. The intensity of the light emitted from the optical element is measured by applying an injection current to the optical element, a relative radiative efficiency is calculated from a ratio of the intensity of the emitted light to the injection current, the maximum relative radiative efficiency and the maximum injection current corresponding to the maximum relative radiative efficiency are obtained, a reference injection current for minimizing an amount of change of a recombination coefficient in an active layer of the optical element in correspondence with a carrier density change in the active layer of the optical element is extracted from data of injection currents that are equal to or less than the maximum injection current and data of relative radiative efficiencies that are equal to or less than the maximum relative radiative efficiency, a reference internal quantum efficiency of the optical element is calculated from the reference injection current, and internal quantum efficiencies of the optical element in various injection currents are calculated from the reference internal quantum efficiency.