UV LED P-Electrode Stack Balancing Reflectance and Ohmic Contact
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional light emitting elements with group III nitride semiconductors for ultraviolet LEDs face challenges in achieving high ultraviolet reflectance and ohmic contact with p-AlGaN or p-GaN layers, leading to increased contact resistance and potential diffusion issues.
Innovation Solution
A light emitting element design featuring a p-electrode with a contact layer of Ru or Ni/Au and a reflection layer of Al or its alloy, stacked in a specific thickness and structure to enable ohmic contact and high ultraviolet reflectance, along with a manufacturing method that includes heat treatment to reduce contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a single Al layer is used for the p-electrode, then high ultraviolet reflectance is achieved, but ohmic contact with p-AlGaN or p-GaN cannot be made
Solution Approach 1:
The p-electrode is segmented into multiple layers with distinct functions: the Al layer provides high ultraviolet reflectance, while the Ru or Ni/Au layer provides ohmic contact capability. This segmentation allows each layer to optimize its specific function without compromising the other.
Solution Approach 2:
The p-electrode uses a composite structure combining Al with Ru or Ni/Au. The Al layer reflects ultraviolet light effectively, while the Ru or Ni/Au layer forms an ohmic contact with the p-type semiconductor layer, creating a composite electrode that achieves both high reflectance and low contact resistance.
2Reliability
If Al is diffused into the p layer, then contact resistance may be reduced, but the contact resistance may be deteriorated due to excessive diffusion
Solution Approach 1:
The Ru or Ni/Au layer acts as an intermediary between the Al layer and the p-type semiconductor layer. It enables ohmic contact formation through controlled interaction with the semiconductor, while preventing excessive Al diffusion that would deteriorate contact resistance and compromise layer composition stability.
3Reliability
If the contact layer thickness is increased, then ohmic contact is improved, but ultraviolet reflectance is reduced
Solution Approach 1:
The thickness of the Ru or Ni/Au contact layer is optimized to a specific range (0.5 nm to 6 nm) to achieve the right balance: thick enough to provide sufficient ohmic contact, but thin enough to allow the Al layer to maintain high ultraviolet reflectance. This parameter optimization resolves the contradiction between contact quality and optical performance.
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 achieves a contact resistivity of 2×10−3 Ω·cm2 or less and reflectance of 55% or more in the ultraviolet region, improving light extraction efficiency and reducing forward voltage while maintaining effective ohmic contact.
Implementation Method 1
a contact layer that is provided in contact with the p layer, has a thickness of 0.5 nm or more and 6 nm or less, and is made of Ru or Ni/Au
Implementation Method 2
a reflection layer that is provided in contact with the contact layer, has a thickness of 50 nm or more, and is made of Al or an alloy mainly containing Al
Implementation Method 3
a heat treatment process of performing heat treatment to reduce contact resistance to the p layer
Data Source
AI summary
A light emitting element includes a group III nitride semiconductor with an emission wavelength of 200 nm or more and 280 nm or less, the light emitting element includes: a semiconductor layer in which an n layer, a light emitting layer, and a p layer are provided in this order; and a p-electrode provided on and in contact with the p layer, and the p-electrode includes a contact layer that is provided in contact with the p layer, has a thickness of 0.5 nm or more and 6 nm or less, and contains Ru or Ni/Au, and a reflection layer that is provided in contact with the contact layer, has a thickness of 50 nm or more, and contains Al or an alloy mainly containing Al.