Superlattice P-Type Contact Layer for Deep UV Reliability
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Solution Overview
Problem
Deep ultraviolet light-emitting devices with high Al-composition ratio p-type contact layers experience sudden power output deterioration and reliability issues due to increased absorption and lattice strain, leading to 'sudden death' during overload tests.
Innovation Solution
A p-type contact layer with a superlattice structure is implemented, comprising alternating layers of AlxGa1-xN and AlyGa1-yN, optimized by specific Al composition ratios and thicknesses to enhance transmittance and reliability, satisfying the formulas 0.030<z−w0<0.20 and 0.050≤x−y≤0.47, where z is the average Al composition ratio and x and y are the Al composition ratios of the respective layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the Al-composition ratio of the p-type contact layer is increased to improve transmittance for deep ultraviolet light, then out-coupling efficiency is improved, but lattice strain increases leading to sudden device failure
Solution Approach 1:
The p-type contact layer is segmented into multiple sub-layers with different Al-composition ratios. The first p-type contact layer has a lower Al-composition ratio (0.1 to 0.3) to reduce lattice strain, while the second p-type contact layer has a higher Al-composition ratio (0.4 to 0.6) to improve transmittance. This segmentation allows each layer to fulfill its specific function without causing harmful effects.
Solution Approach 2:
Different regions of the p-type contact layer structure are assigned different Al-composition ratios optimized for their specific functions. The first contact layer region is optimized for strain management, while the second contact layer region is optimized for optical transmittance. This local quality differentiation resolves the contradiction between reliability and transmittance.
2Power
If the Al-composition ratio of the p-type contact layer is increased to improve transmittance, then power output is improved, but sudden death phenomenon occurs during overload tests
Solution Approach 1:
The p-type contact layer is divided into two distinct layers with different Al-composition ratios. The first layer with lower Al-content provides structural stability and strain management, preventing sudden death during overload. The second layer with higher Al-content provides the necessary transmittance for high power output. This segmentation enables both high power and reliability.
Solution Approach 2:
The p-type contact layer structure functions as a composite material system where two different AlGaN compositions are combined. The lower-Al layer provides mechanical and structural properties, while the higher-Al layer provides optical properties. This composite approach achieves both high power output and resistance to sudden death phenomenon.
3Reliability
If a single-layer p-type contact layer with high Al-composition ratio is used to improve transmittance, then out-coupling efficiency increases, but device complexity increases due to need for additional layers
Solution Approach 1:
The contact layer is segmented into two functional layers, each with optimized Al-composition ratio. This segmentation achieves both high transmittance and reliability without requiring additional complex structures such as buffer layers or intermediate layers, as the two-layer design integrates multiple functions within the contact layer itself.
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 superlattice structure p-type contact layer achieves high power output while ensuring excellent reliability by maintaining transmittance and reducing lattice strain, preventing sudden power drops and device failure during overload tests.
Implementation Method 1
the use of a p-type contact layer made of AlGaN allows the p-type contact layer to have increased transmittance for emission light
Implementation Method 2
maintaining transmittance and reducing lattice strain, preventing sudden power drops and device failure during overload tests
Data Source
AI summary
Disclosed is a deep ultraviolet light-emitting device which includes on a substrate 10 in order: an n-type semiconductor layer 30, a light-emitting layer 40, a p-type electron block layer 60, and a p-type contact layer 70, wherein the p-type contact layer 70 comprises a superlattice structure having an alternating stack of: a first layer 71 made of AlxGa1-xN having an Al composition ratio x higher than an Al composition ratio w0 of a layer configured to emit deep ultraviolet light in the light-emitting layer; and a second layer 72 made of AlyGa1-yN having an Al composition ratio y lower than the Al composition ratio x, and the Al composition ratio w0, the Al composition ratio x, the Al composition ratio y, and a thickness average Al composition ratio z of the p-type contact layer satisfy the formula [1] 0.030<z−w0<0.20 and the formula [2] 0.050≤x−y≤0.47.