LED Light Extraction via Reflective Insulating Layer
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Solution Overview
Problem
Conventional LEDs experience light loss due to internal total reflection at side surfaces and absorption/reflection by electrodes, and Ag-based reflection layers are prone to thermal issues and limited reflectance.
Innovation Solution
The design includes a semiconductor stack with a p-type and n-type compound semiconductor layer, a reflective insulating layer between electrodes, and surface roughening to enhance light extraction, using a reflective insulating layer with higher reflectance than Ag and preventing light absorption by electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional vertical-type LED structure with Ag reflection layer is used, then ohmic contact and electrical conductivity are achieved, but light extraction efficiency deteriorates due to absorption and reflection by electrodes
Solution Approach 1:
A transparent conductive oxide layer (ITO, IZO, or ZnO) is introduced as an intermediary between the metal electrode and the semiconductor layer. This intermediate layer serves dual purposes: maintaining electrical conductivity while being transparent to light, thereby preventing light absorption and reflection by the metal electrode.
Solution Approach 2:
The electrode structure uses a composite configuration combining metal layers (for conductivity) with transparent conductive oxide layers (for light transmission). This composite structure achieves both electrical functionality and optical transparency, resolving the contradiction between conductivity and light extraction efficiency.
2Reliability
If Ag is used to form a reflection layer for ohmic contact, then electrical contact is achieved, but thermal stability deteriorates due to Ag aggregation during thermal treatment
Solution Approach 1:
The transparent conductive oxide layer acts as a protective intermediary between the Ag reflection layer and the thermal processing environment. This intermediate barrier prevents direct thermal exposure of Ag, reducing aggregation and migration during thermal treatment while maintaining electrical contact functionality.
Solution Approach 2:
The patent applies a protective transparent conductive oxide coating beforehand to cushion the Ag layer from thermal damage. This pre-protective measure prevents Ag aggregation during subsequent thermal processing steps, ensuring long-term structural stability.
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 improves light extraction efficiency by directing light away from the substrate and preventing absorption by electrodes, offering enhanced reflectance and stability compared to conventional LEDs.
Implementation Method 1
a reflective insulating layer positioned between the p-electrode and the n-electrode, to insulate the p-electrode from the n-electrode and to reflect light away from the support substrate
Implementation Method 2
the surface of the exposed n-type layer 23 is roughened using a dry or photo-enhanced chemical (PEC) etching technique, thereby enhancing the light extraction efficiency
Data Source
AI summary
Provided is a high-efficiency light emitting diode (LED) that includes: a support substrate; a semiconductor stack positioned on the support substrate, the semiconductor stack including a p-type compound semiconductor layer, an active layer, and an n-type compound semiconductor layer; a first electrode positioned between the support substrate and the semiconductor stack and in ohmic contact with the semiconductor stack; a first bonding pad positioned on a portion of the first electrode that is exposed outside of the semiconductor stack; and a second electrode positioned on the semiconductor stack. Protrusions are formed on exposed surfaces of the semiconductor stack. In addition, the second electrode may be positioned between the first electrode and the support substrate and contacted with the n-type compound semiconductor layer through openings of the semiconductor stack.