AlGaN p-type contact layer for UV LED reliability
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Solution Overview
Problem
Group III nitride semiconductor light emitting elements with p-type contact layers made of AlGaN experience a sudden drop in light output power, known as 'sudden death,' which affects their reliability and makes mass production unfeasible, unlike those with GaN contact layers.
Innovation Solution
A group III nitride semiconductor light emitting element with a p-type contact layer made of AlxGa1-xN, where the Al composition ratio x satisfies the condition 2.09−0.006×λp≤x≤2.25−0.006×λp, and a thickness of 20 nm or greater and 80 nm or smaller, is used, ensuring no sudden death and improved light output power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the Al composition ratio of the p-type contact layer is increased to improve transmittance and light extraction efficiency, then light extraction efficiency is improved, but light output power suddenly drops to nearly half (sudden death)
Solution Approach 1:
The patent applies parameter changes by precisely controlling the Al composition ratio x within the range 0.05 ≤ x ≤ 0.35 and thickness within 20-80 nm. This quantitative parameter optimization resolves the contradiction by finding the optimal balance point where transmittance is sufficiently high for good light extraction, but the composition remains stable enough to prevent sudden death. The specific numerical ranges provide a clear design guideline that simultaneously addresses both light extraction efficiency and operational reliability.
Solution Approach 2:
The patent uses composite material design by creating an AlGaN mixed crystal contact layer that combines AlN and GaN components. This composite approach allows tuning of optical and electrical properties: the AlN component provides high transmittance for UV light extraction, while the GaN component maintains adequate hole density for electrical contact. The synergistic combination resolves the contradiction between optical performance and electrical stability.
2Illumination intensity
If the Al composition ratio of the p-type contact layer is increased to improve transmittance, then transmittance increases, but hole density decreases
Solution Approach 1:
The patent applies parameter changes by optimizing the Al composition ratio x within the specific range 0.05 ≤ x ≤ 0.35. This quantitative control allows the material to maintain adequate hole density for electrical contact while achieving sufficient transmittance for light extraction. The lower bound (x≥0.05) ensures enough GaN character for hole transport, while the upper bound (x≤0.35) ensures enough AlN character for transmittance.
Solution Approach 2:
The AlGaN mixed crystal acts as a composite material where the GaN component contributes to hole density and the AlN component contributes to transmittance. By adjusting the mixing ratio (composition parameter x), both properties can be simultaneously optimized. This composite approach resolves the contradiction by allowing each component to fulfill its functional role without completely sacrificing the other property.
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 provides a group III nitride semiconductor light emitting element with higher light output power and reliability by regulating the Al composition ratio and thickness of the p-type contact layer, preventing sudden death and enhancing external quantum efficiency.
Implementation Method 1
the transmittance of the p-type contact layer to short-wavelength light increases with an increase in the Al composition ratio of the p-type contact layer made of AlGaN
Implementation Method 2
a reflection electrode that is reflective to radiated light from a light-emitting layer
Implementation Method 3
light emitting elements having light emitting layers made of group III nitride semiconductors can be provided for wide wavelength ranges from deep ultraviolet light to visible light
Data Source
AI summary
Provided are a group III nitride semiconductor light emitting element and a method of manufacturing the same. A group III nitride semiconductor light emitting element of the present disclosure comprises in this order, in a substrate, an n-type semiconductor layer, a light emitting layer, a p-type electron blocking layer, a p-type contact layer made of AlxGa1-xN, and a p-side reflection electrode, wherein a center emission wavelength of light emitted from the light emitting layer is 270 nm or greater and 330 nm or smaller, the p-type contact layer is in contact with the p-side reflection electrode, and has a thickness of 20 nm or greater and 80 nm or smaller, and the Al composition ratio x of the p-type contact layer satisfies the following Formula:2.09−0.006×λp≤x≤2.25−0.006×λp where λp is the center emission wavelength in nanometer.