Semiconductor Heterostructure Refractive-Index Grading for Light Extraction
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Solution Overview
Problem
Semiconductor light emitting devices, such as LEDs and laser diodes, face inefficiencies due to Fresnel reflective losses associated with total internal reflection (TIR) at interfaces between semiconductor layers, leading to light trapping and absorption.
Innovation Solution
A semiconductor heterostructure is designed with carefully selected refractive indices for its layers to eliminate TIR, where the first semiconductor layer has a higher index than the second and third layers, and the active region is optimized with quantum wells and barriers to reduce Fresnel losses, potentially incorporating boron nitride to adjust refractive indices and enhance optical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If semiconductor layers are used with different molar fractions to control band gap, then light generation is enabled, but total internal reflection and Fresnel losses increase causing light trapping
Solution Approach 1:
The patent introduces an intermediate layer with a refractive index that is lower than both the active region and the substrate, serving as a mediator to reduce the abrupt refractive index change at the interface. This intermediate layer acts as a transition zone that minimizes total internal reflection and Fresnel losses, allowing more light to escape the device while maintaining the band gap control achieved through different molar fractions in the active region.
2Manufacturing precision
If a discrete change in molar fractions is used at layer interfaces, then band gap control is achieved, but abrupt changes in optical properties cause light trapping
Solution Approach 1:
The patent applies local quality by creating a graded composition layer with gradually changing molar fractions between the active region and the substrate. Instead of a discrete abrupt interface, the composition is locally adjusted across multiple sub-layers with incrementally changing aluminum and indium contents. This local variation in composition provides a gradual transition of refractive index, reducing light trapping while maintaining precise band gap control through the graded structure.
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
This approach significantly reduces Fresnel reflective losses, improving light emission efficiency by allowing more light to escape without internal reflection, thereby enhancing the performance of light emitting diodes.
Implementation Method 1
Fresnel losses associated with high total internal reflection limit efficiencies of light emitting diodes
Implementation Method 2
A larger change in the index of refraction between the layers, and between the substrate and its surroundings, results in a smaller total internal reflection (TIR) angle
Data Source
AI summary
A semiconductor heterostructure for an optoelectronic device with improved light emission is disclosed. The heterostructure can include a first semiconductor layer having a first index of refraction n1. A second semiconductor layer can be located over the first semiconductor layer. The second semiconductor layer can include a laminate of semiconductor sublayers having an effective index of refraction n2. A third semiconductor layer having a third index of refraction n3 can be located over the second semiconductor layer. The first index of refraction n1 is greater than the second index of refraction n2, which is greater than the third index of refraction n3.