GaN LED with Surface Protrusions for Dislocation Reduction
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Solution Overview
Problem
High dislocation density in nitride semiconductor layers grown on heterogeneous substrates, such as sapphire, limits the efficiency of light emitting diodes due to lattice mismatch and thermal expansion differences, leading to reduced emission efficiency and current concentration issues known as the droop phenomenon.
Innovation Solution
A high efficiency light emitting diode with a vertical structure is fabricated using a gallium nitride substrate, featuring a semiconductor stacked structure with protrusions or recesses and fine cones, which reduces dislocation density to 5×10^6/cm², improving current dispersion and light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If nitride semiconductor layers are grown on heterogeneous substrates such as sapphire, then the substrate can be easily separated due to different physical properties, but the epitaxial layer has high dislocation density due to lattice mismatch and thermal expansion differences
Solution Approach 1:
The patent introduces a buffer layer as an intermediary between the sapphire substrate and the nitride semiconductor layer. This buffer layer mediates the lattice mismatch and thermal expansion differences, reducing dislocation density while maintaining the ease of substrate separation through the heterogeneous substrate interface.
Solution Approach 2:
The patent modifies the growth parameters and structure of the epitaxial layer by introducing the buffer layer with specific thickness and composition. This changes the physical parameters of the interface, reducing dislocation propagation from the substrate while maintaining manufacturability.
2Length of stationary object
If the epitaxial layer thickness is kept thin at several micrometers, then the device structure is compact, but current cannot be spread effectively and concentrates at dislocations causing droop phenomenon
Solution Approach 1:
The patent addresses the current spreading problem in the thin epitaxial layer by introducing surface structures (protrusions or recesses) that create additional current pathways. This dimensional modification allows current to disperse laterally across the surface area, compensating for the limited thickness and preventing concentration at dislocation sites.
3Device complexity
If current is concentrated at dislocations, then the device structure remains simple, but internal quantum efficiency reduces due to droop phenomenon
Solution Approach 1:
The patent applies local quality modification by creating protrusions or recesses at specific locations on the epitaxial layer surface. These localized structural changes redirect current flow away from dislocation-prone areas and toward regions with better electrical properties, improving internal quantum efficiency without requiring complex overall device restructuring.
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 approach results in a light emitting diode with reduced droop effect and enhanced light extraction efficiency, maintaining high efficiency even at high currents, with the semiconductor stacked structure grown on a gallium nitride substrate exhibiting less than 20% droop at 350 mA.
Implementation Method 1
A high efficiency light emitting diode with a vertical structure is fabricated using a gallium nitride substrate, featuring a semiconductor stacked structure with protrusions or recesses and fine cones, which reduces dislocation density to 5×10^6/cm²
Implementation Method 2
a semiconductor stacked structure disposed on the support substrate and including a gallium nitride-based p-type semiconductor layer, a gallium nitride-based active layer, and a gallium nitride-based n-type semiconductor layer
Data Source
AI summary
Disclosed herein are a high efficiency light emitting diode and a method of fabricating the same. The light emitting diode includes a semiconductor stacked structure disposed on the support substrate and including a gallium nitride-based p-type semiconductor layer, a gallium nitride-based active layer, and a gallium nitride-based n-type semiconductor layer; and a reflecting layer disposed between the support substrate and the semiconductor stacked structure, wherein the semiconductor stacked structure includes a plurality of protrusions having a truncated cone shape and fine cones formed on top surfaces of the protrusions. By this configuration, light extraction efficiency of the semiconductor stacked structure having low dislocation density can be improved.