LED Reflective Contact Structure for Higher Light Extraction
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Solution Overview
Problem
Conventional semiconductor LEDs face inefficiencies in light extraction due to total internal reflection and absorption issues, particularly in flip-chip configurations where light is not effectively reflected back into the diode region, leading to reduced external efficiency.
Innovation Solution
The implementation of a hybrid reflective structure comprising a transparent insulating layer and a reflective layer with an index mismatch, which enhances total internal reflection by providing an index step, combined with a reflective anode and cathode contact configuration that collectively reflects light back into the diode region, minimizing absorption and maximizing light extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional LED structure is used, then device simplicity is maintained, but light extraction efficiency deteriorates due to total internal reflection and absorption
Solution Approach 1:
A transparent insulating layer is introduced as an intermediary between the reflective layer and the semiconductor layers. This intermediary layer provides an index of refraction mismatch that enhances total internal reflection at the interface, thereby improving light extraction efficiency without complicating the overall device structure or manufacturing process
Solution Approach 2:
The patent employs a composite reflective structure combining a metallic reflective layer (such as aluminum or silver) with a transparent insulating layer (such as silicon dioxide or silicon nitride). This composite structure leverages the high reflectivity of the metal combined with the refractive index properties of the insulator to maximize light extraction while maintaining structural simplicity
2Loss of energy
If reflective layer is added to improve light extraction, then light extraction efficiency is improved, but device complexity increases
Solution Approach 1:
The transparent insulating layer serves multiple functions simultaneously: it acts as an optical intermediary to enhance total internal reflection, provides electrical insulation between the reflective layer and semiconductor layers, and offers structural support. By merging these functions into a single layer, the patent improves light extraction without proportionally increasing device complexity
3Loss of energy
If reflective structure is implemented, then external efficiency is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent optimizes the thickness of the transparent insulating layer to be between 50-500 nanometers, a parameter range that maximizes the optical interference effect for enhancing total internal reflection while being sufficiently robust for standard semiconductor manufacturing processes. This parameter optimization balances performance improvement with manufacturing feasibility
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 enhances the external efficiency of semiconductor LEDs by reducing light loss through total internal reflection and absorption, particularly in flip-chip configurations, by reflecting a high percentage of emitted light back into the diode region for re-emission, thereby improving the overall light extraction efficiency.
Implementation Method 1
The transparent insulating layer and the reflective layer can provide a hybrid reflective structure or 'hybrid mirror', wherein the underlying transparent insulating layer provides an index of refraction mismatch or index step to enhance the total internal reflection (TIR) from the diode region
Implementation Method 2
A reflective layer electrically contacts the one of then-type layer or the p-type layer, and extends on the transparent insulating layer
Data Source
Figure 1
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Figure 3~4
AI summary
Light emitting diodes include a diode region having first (110a) and second (110b) opposing faces that include therein an n-type layer (112) and a p-type layer (116), an anode contact (130) that ohmically contacts the p-type layer (114) and extends on the first face, and a cathode contact (150) that ohmically contacts the n-type layer (112) and also extends on the first face. The anode contact and/or the cathode contact may further provide a hybrid reflective structure on the first face that is configured to reflect substantially all light that emerges from the first face back into the first face. Related fabrication methods are also described.