UV LED Tunnel Junction Patterned for Ohmic Resistance
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Solution Overview
Problem
Conventional UV LEDs face challenges in achieving high luminous flux and efficiency due to light absorption by the p-GaN layer and high ohmic contact resistance, particularly for wavelengths less than 380 nm, where existing P-type ohmic contact metals like Cr, Ti, and Ni have poor reflectivity.
Innovation Solution
A UV semiconductor light-emitting device with a multi-layer tunnel junction and patterned structure is fabricated, featuring a low work function reflecting layer and an optical phase matching layer to reduce ohmic contact resistance and UV absorption, enhancing luminance and reflectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional P-type ohmic contact metal (Cr, Ti, Ni) is used to reduce contact resistance, then ohmic contact performance is improved, but UV reflectivity deteriorates
Solution Approach 1:
The contact structure is divided into multiple functional layers: a P-type ohmic contact metal layer (Cr, Ti, or Ni) for electrical contact, and a separate UV-reflective metal layer (Al, Ag, or Au) for optical reflection. This segmentation allows each layer to perform its specialized function without compromising the other.
Solution Approach 2:
The patent introduces a UV-reflective metal layer as an intermediary between the P-type semiconductor layer and the external UV environment. This intermediary layer mediates between the electrical contact requirement (handled by the ohmic contact metal) and the optical reflection requirement, solving the contradiction by adding a functional buffer layer.
2Reliability
If the p-GaN layer is present at the surface to facilitate carrier injection, then electrical performance is improved, but UV light emission is absorbed
Solution Approach 1:
The patent extracts or removes the p-GaN surface layer in the electrode region to eliminate the harmful UV absorption. By taking out the light-absorbing material from the light extraction path, the device achieves both good electrical contact and high UV extraction efficiency.
Solution Approach 2:
The patent addresses the conflict between electrical function and optical function by changing the spatial dimension - removing the p-GaN layer specifically in the vertical dimension at the electrode contact region, while maintaining it in other regions where it provides electrical functionality without interfering with light extraction.
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 solution effectively improves luminous flux and reduces resistance, enabling high-performance UV light-emitting devices with wavelengths between 100-380 nm by utilizing a tunnel junction, optical phase matching layer, and low work function reflecting materials, thereby increasing reflectivity and luminance.
Implementation Method 1
a multi-layer tunnel junction over the light-emitting epitaxial layer surface
Implementation Method 2
an optical phase matching layer over the surface layer of the light-emitting epitaxial structure and penetrates the UV
Implementation Method 3
a reflecting layer, covering the entire tunnel junction and the optical phase matching layer
Data Source
AI summary
An ultraviolet semiconductor light emitting device includes: a light-emitting epitaxial layer including an n-type semiconductor layer, a light-emitting layer, and a p-type semiconductor layer; a tunnel junction at a non-light-emitting surface of the light-emitting epitaxial layer and having a patterned structure with openings to expose the light-emitting epitaxial layer; an optical phase matching layer over a surface layer of the light-emitting epitaxial layer and transmissive of UV light; and a reflecting layer covering the entire tunneling junction and the optical phase matching layer. A patterned structure is provided over the tunnel junction for full-angle light reflection. Part of the tunneling junction forms ohmic contact with the low work function reflecting metal. The patterned distribution design can effectively reduce the ohmic contact resistance.