UV Light Emitter AlGaN Stack for Low-Voltage Conductivity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional ultraviolet light-emitting elements with AlN single crystal substrates have high dislocation densities, leading to increased driving voltage due to reduced n-type AlGaN layer conductivity.
Innovation Solution
A light-emitting device with a stacked structure of multiple n-type AlXGa1-X layers (0.5 ≤ X < 1) on an AlN single crystal substrate, each with varying Al composition, maintains lattice-matching and high crystallinity, improving horizontal conductivity and reducing dislocation density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single n-type AlGaN layer with high Al composition is formed on an AlN single crystal substrate to maintain lattice-matching, then crystal quality and surface smoothness are improved, but the film thickness is limited which reduces horizontal conductivity and increases driving voltage
Solution Approach 1:
The patent divides the n-type AlGaN layer into multiple sub-layers with different Al compositions (X1, X2, X3 where 0.5≤X1<X2<X3<1). Each sub-layer maintains lattice-matching with the AlN substrate individually, allowing each layer to achieve optimal crystal quality while the stacked structure provides sufficient total thickness for high horizontal conductivity. This segmentation resolves the contradiction by enabling both thin individual layers (for crystal quality) and thick total structure (for conductivity).
Solution Approach 2:
Different regions of the n-type AlGaN structure have different Al compositions optimized for their specific functions. The lower Al composition layers (X1, X2) provide a gradient transition from the substrate, reducing dislocation density, while the upper layer with higher Al composition (X3) maintains lattice-matching and optimizes crystal quality. This local optimization of composition at different positions allows simultaneous achievement of crystal quality and conductivity requirements.
2Reliability
If the film thickness of n-type AlGaN layer is increased to improve horizontal conductivity and reduce driving voltage, then conductivity is improved, but lattice-matching with AlN substrate is lost leading to increased dislocation density
Solution Approach 1:
By segmenting the thick n-type AlGaN layer into multiple sub-layers with progressively increasing Al composition, the patent maintains lattice-matching at each interface with the AlN substrate. The total thickness can be large (sum of all sub-layers) for high conductivity, while each individual sub-layer remains thin enough to maintain lattice-matching, thus preventing dislocation density increase.
Solution Approach 2:
The patent changes the Al composition parameter (X) across different sub-layers, creating a gradient structure where X1<X2<X3. This parameter change allows each layer to have optimal lattice-matching with the substrate while collectively achieving the required total thickness for high horizontal conductivity, resolving the contradiction between thickness and lattice-matching.
3Manufacturing precision
If Al composition in n-type AlGaN layer is increased to maintain lattice-matching with AlN substrate, then crystal quality is improved, but the layer thickness must be reduced which lowers horizontal conductivity
Solution Approach 1:
The patent segments the structure into multiple n-type AlGaN layers with different Al compositions. The lower layers with lower Al composition can be thicker and provide gradient transition, while the upper layer with higher Al composition (closer to lattice-matching condition) can be optimized for crystal quality. The cumulative thickness of all segments provides sufficient horizontal conductivity while individual segments maintain crystal quality.
Solution Approach 2:
The patent creates a composite n-type AlGaN structure where multiple layers with different Al compositions are stacked together. This composite structure combines the advantages of each composition: lower Al composition layers provide thickness and conductivity, while higher Al composition layers maintain lattice-matching and crystal quality. The composite nature allows simultaneous achievement of both crystal quality and conductivity.
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 results in ultraviolet light-emitting elements with lower driving voltage, higher emission efficiency, and improved reliability by enhancing n-type conductivity and reducing dislocation density.
Implementation Method 1
crystal-growth of an AlA Ga1-A N layer on a single crystal substrate
Implementation Method 2
the n-type AlGaN layers may be lattice-matched to the AlN single crystal substrate
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
Provided is a group III nitride stacked body having an n-type AlXGa1-XN (0.5 ≤ X < 1) layer formed on an AlN single crystal substrate while being lattice-matched to the AlN single crystal substrate wherein the n-type AlXGa1-XN (0.5 ≤ X < 1) layer has at least a stacked structure in which a first n-type AlX1Ga1-X1N (0.5 ≤ X1 < 1) layer, a second n-type AlX2Ga1-X2N (0.5 ≤ X2 < 1) layer, and a third n-type AlX3Ga1-X3N (0.5 ≤ X3 < 1) layer are stacked in this order from the AlN single crystal substrate side, and X1, X2, and X3 indicating the Al compositions of the respective layers satisfy 0 < |X1 - X2| ≤ 0.1, and satisfy 0 < |X2 - X3| ≤ 0.1.