Vertical GaN LED Ag Reflective Electrode Light Extraction
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Solution Overview
Problem
Vertical GaN-based light emitting diodes require a highly reflective p-type electrode with low contact resistance and high thermal stability to achieve high optical output, as Au-based electrodes used in horizontal diodes are not suitable due to low reflectivity, and existing solutions fail to enhance optical output effectively.
Innovation Solution
An Ag-based highly reflective p-type electrode combined with quasi-photonic crystals and surface roughening techniques, such as forming pores or hexagonal pyramids on the n-type semiconductor layer, to minimize total internal reflection and increase light extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Au-based p-type electrodes (Ni/Au, Pd/Au, Pt/Au) are used in vertical GaN-based LEDs, then contact resistance is reduced, but reflectivity decreases to 40% or less
Solution Approach 1:
The patent changes the material parameter from Au-based to Ag-based electrode, exploiting the fundamentally different optical properties of silver which provides both low contact resistance and high reflectivity (>90%) in the blue-green spectrum range
Solution Approach 2:
The patent employs composite electrode structures such as Ag/Pd, Ag/Pt, or Ag/Al2O3 combinations that leverage the low contact resistance of Ag while using the overlayer to prevent Ag diffusion and enhance thermal stability, achieving both low contact resistance and high reflectivity
2Ease of manufacture
If a smooth n-type semiconductor layer surface is used, then manufacturing is simplified, but total internal reflection occurs at the interface, reducing light emission
Solution Approach 1:
The patent introduces curved or non-planar surface structures including hemispherical bumps, pyramids, and inverted cones on the n-type semiconductor layer, which transform the flat interface into a curved surface that reduces total internal reflection and enhances light extraction efficiency
Solution Approach 2:
The patent creates porous or textured surfaces on the n-type semiconductor layer through chemical etching or self-organization processes, forming arrays of nanoscale pores or protrusions that increase the effective surface area and reduce reflection by creating gradual refractive index transitions
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
The combination results in a significant increase in optical output, up to 9 times that of conventional diodes, demonstrating the Ag-based electrode's primary role in enhancing performance when used with surface reformation techniques.
Implementation Method 1
a p-type ohmic electrode layer formed between a substrate and a p-type semiconductor layer must be a highly reflective electrode which can achieve total non-absorptive reflection
Implementation Method 2
When an n-type semiconductor layer has a smooth and flat surface, a considerable amount of light generated in an active layer cannot be emitted due to total internal reflection occurring at an interface between the atmosphere and a semiconductor layer
Implementation Method 3
pores or protrusions, several hundred nanometers to several microns in size, are repeatedly arranged on the surface of the n-type semiconductor by lithography to form photonic crystals thereon
Data Source
AI summary
The present disclosure provides a vertical GaN-based semiconductor diode and a method of manufacturing the same. The GaN-based πi-V group semiconductor device includes a substrate, a p-type ohmic electrode layer on the substrate, a p-type GaN-based πi-V group compound semiconductor layer on the p-type ohmic electrode layer, an n-type GaN-based πi-V group compound semiconductor layer on the p-type GaN-based πi-V group compound semiconductor layer, and an n-type ohmic electrode layer on the n-type GaN-based IE-V group compound semiconductor layer. The p-type ohmic electrode layer is an Ag-based highly reflective electrode having a high reflectivity of 70% or more, and a surface of the n-type GaN-based E-V group compound semiconductor layer is subjected to at least one of a process of forming photonic crystals and a process of surface roughening.