Semiconductor Light Emitting Element Diffractive Face
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Solution Overview
Problem
Existing semiconductor light emitting diodes face challenges in maximizing light extraction efficiency due to the high refractive index of semiconductors, leading to significant light being trapped through total and Fresnel reflections.
Innovation Solution
A semiconductor light emitting element is designed with a diffractive face on the substrate surface featuring convex or concave portions with a period longer than the optical wavelength but shorter than the coherent length, combined with a reflective face to diffract and reflect light, enhancing light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a concavo-convex structure with period equal to or smaller than twice the optical wavelength is provided on the semiconductor surface, then light extraction efficiency is improved by suppressing Fresnel reflection through photonic crystal or moth-eye structure, but the light extraction efficiency is still limited and cannot be further increased
Solution Approach 1:
The invention divides the light extraction function into two distinct components: a diffractive face with convex portions that diffracts light into multiple directions, and a reflective face that reflects diffracted light back toward the extraction surface. This segmentation allows each component to perform its specific function optimally, overcoming the limitations of single-structure approaches
Solution Approach 2:
The invention transitions from two-dimensional surface patterning (concavo-convex structures) to three-dimensional light manipulation by introducing a reflective face beneath the diffractive face. This creates a vertical cavity structure that guides light through multiple interactions, extracting light that would otherwise be trapped by total internal reflection
2Loss of energy
If the period of convex portions or concave portions is set longer than the optical wavelength but shorter than the coherent length, then diffractive effects are enhanced to redirect light out of the diode, but the structural precision requirements increase
Solution Approach 1:
The invention specifies optimal parameter ranges for the period (longer than optical wavelength but shorter than coherent length) and dimensions of convex portions to maximize diffractive effects. By carefully controlling these parameters, the structure achieves high light extraction efficiency while remaining manufacturable through standard semiconductor fabrication techniques
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 configuration significantly increases light extraction efficiency by utilizing diffractive effects to redirect light out of the diode, improving output beyond previous concavo-convex structures and scattering methods.
Implementation Method 1
a diffractive face that light emitted from the light emitting layer is incident to, having convex portions or concave portions formed in a period which is longer than an optical wavelength of the light and is shorter than a coherent length of the light, is formed on a main surface side of the substrate
Implementation Method 2
a reflective face which reflects light diffracted at the diffractive face and let this light be incident to the diffractive face again is formed on a back surface side of the substrate
Data Source
Figure 1
Figure 2(a)~2(c)
Figure 3(a)~3(e)
AI summary
[PROBLEM] A light extraction efficiency increases by suppressing a reflection of a semiconductor layer and a transparent substrate. [MEANS FOR SOLVING] A semiconductor light emitting element comprising a semiconductor stack (19) part including a light emitting layer, a diffractive face (2a) that light emitted from the light emitting layer is incident to, that convex portions (2c) are formed in a period which is longer than optical wavelength of the light and is shorter than coherent length of the light, and a reflective face which reflects light diffracted at the diffractive face and let this light be incident to the diffractive face again. The convex portions (2c) have a flat upper surface (2f) which is parallel to the main surface side.