Angled Substrate Sidewalls for LED Light Extraction
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Solution Overview
Problem
Semiconductor light emitting devices face efficiency losses due to light absorption by the epitaxial structure, particularly when a phosphor layer emits light back towards a non-reflective surface, reducing the overall light extraction efficiency.
Innovation Solution
The substrate is shaped with angled sidewalls, with a reflective layer on one sidewall and a wavelength converting layer on the other, disposed in a cavity mount with a heat-conducting reflective layer, to direct light extraction away from the epitaxial structure and minimize absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If light is extracted from the substrate side through a planar surface, then the device structure is simple, but light absorption by the epitaxial structure increases and light extraction efficiency decreases
Solution Approach 1:
The substrate is transformed from a planar symmetric surface to an asymmetric shaped substrate with a first sidewall at a first angle and a second sidewall at a second angle relative to the major surface. This asymmetric geometry directs light extraction away from the epitaxial structure, reducing absorption losses while maintaining manufacturing feasibility through controlled shaping processes.
Solution Approach 2:
The invention transitions from two-dimensional planar light extraction to three-dimensional angled sidewall extraction. By creating sidewalls at specific angles, light is directed along new geometric paths that bypass the epitaxial structure, effectively adding a dimensional aspect to light extraction that reduces harmful absorption.
2Loss of energy
If a reflective layer is added to the sidewall, then light extraction efficiency improves, but device complexity and manufacturing steps increase
Solution Approach 1:
The reflective layer is applied selectively only to the first sidewall where it is most needed to redirect light away from the epitaxial structure. This localized application provides maximum benefit with minimum added complexity, as the reflective property is concentrated where it produces the greatest reduction in light absorption.
3Duration of action of stationary object
If heat management is improved through a heat conducting reflective layer, then device lifetime increases, but manufacturing complexity increases
Solution Approach 1:
The reflective layer on the first sidewall serves dual functions: it reflects light to improve extraction efficiency and it conducts heat away from the epitaxial structure to enhance device lifetime. This multi-functionality eliminates the need for separate heat management components, maintaining ease of manufacture while achieving both optical and thermal performance improvements.
4Loss of energy
If the substrate is shaped with angled sidewalls, then light extraction efficiency improves, but manufacturing precision requirements increase
Solution Approach 1:
The invention specifies particular angle ranges for the first and second sidewalls that optimize light extraction while remaining compatible with standard manufacturing capabilities. By selecting practical angle parameters rather than extreme values, the design achieves high light extraction efficiency without imposing unrealistic precision requirements on manufacturing processes.
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 enhances light extraction efficiency by reducing absorption and improving heat management, leading to increased light output and extended device lifetime.
Implementation Method 1
A reflective layer is present over the first sidewall. Light is extracted from the substrate through the second sidewall.
Implementation Method 2
A wavelength converting layer is disposed over the second sidewall
Implementation Method 3
The reflective layer is made from a heat conducting material, such that heat is conducted away from the substrate and the semiconductor structure and/or the wavelength converting layer.
Data Source
Figure 1~4
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Figure 7~10
AI summary
Embodiments of the invention include a substrate (10) and a semiconductor structure (12) grown on the substrate. The semiconductor structure includes a light emitting layer (18) disposed between an n-type region (16) and a p-type region (20). The substrate includes a first sidewall (30) and a second sidewall (32). The first sidewall and second sidewall are disposed at different angles relative to a major surface of the semiconductor structure. A reflective layer (34) is disposed over the first sidewall (30).