AlGaN Graded Layer for Deep UV Semiconductor Reliability
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Solution Overview
Problem
Deep ultraviolet optical semiconductor elements face challenges in achieving high light-emitting and receiving efficiencies due to high crystal defect density and increased operation voltage caused by limited AlGaN layer thickness and poor crystalline quality, particularly in n-type AlGaN layers grown on AlN substrates.
Innovation Solution
The optical semiconductor element incorporates a pseudomorphic AlGaN layer with a composition gradient, featuring a first composition gradient layer with an AlN composition ranging from 0.95 to 1 reducing to 0.7 to 0.8, and a second composition gradient layer with a slower reduction rate, grown on an AlN substrate to maintain high crystalline quality and desired layer thickness, thereby reducing electric resistance and operation voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an AlGaN layer with high Al composition is grown on an AlN substrate to achieve high crystalline quality, then the light-emitting and light-receiving efficiencies are improved, but the layer thickness is limited to a critical film thickness (0.5 μm or less) due to compression distortion, causing increased electric resistance and operation voltage
Solution Approach 1:
The patent applies parameter changes by gradually varying the Al composition in the AlGaN layer from high (0.9-1.0) near the AlN substrate to lower (0.3-0.6) toward the active layer. This compositional gradient transforms the abrupt lattice mismatch into a progressive transition, allowing the layer thickness to exceed the critical film thickness while maintaining pseudomorphic growth and high crystalline quality, thereby reducing electric resistance and operation voltage without sacrificing efficiency
Solution Approach 2:
The patent implements local quality by creating different Al composition regions within the AlGaN layer. The region near the AlN substrate has high Al composition (0.9-1.0) to match the substrate lattice and ensure high crystalline quality, while the region toward the active layer has lower Al composition (0.3-0.6) to reduce compression distortion and enable greater thickness. This spatial variation in composition allows each region to optimize its function
2Reliability
If the AlGaN layer thickness is reduced to maintain pseudomorphic state, then crystalline quality is maintained, but electric resistance in lateral direction increases and operation voltage increases
Solution Approach 1:
The patent resolves this contradiction by continuously changing the Al composition parameter through the layer thickness. The compositional gradient allows the layer to maintain pseudomorphic growth (preserving crystalline quality) while accumulating sufficient thickness to provide low-resistance current paths, thereby reducing operation voltage without compromising crystalline quality
3Ease of manufacture
If a uniform Al composition is used in the AlGaN layer, then the growth process is simple, but the layer cannot maintain pseudomorphic state at desired thickness due to compression distortion
Solution Approach 1:
The patent applies parameter changes by implementing a compositional gradient in the AlGaN layer, where the Al composition varies continuously from high (0.9-1.0) near the substrate to lower (0.3-0.6) toward the active layer. This gradient approach enables precise control of layer thickness beyond the critical film thickness while maintaining pseudomorphic growth and high crystalline quality, resolving the contradiction between growth simplicity and thickness control precision
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
This approach enables deep ultraviolet optical semiconductor elements with improved light-emitting and receiving efficiencies, reduced operation voltage, and enhanced crystalline quality by gradually varying the Al composition, preventing distortion and Fresnel reflection, thus optimizing the n-type AlGaN layer thickness and conductivity.
Implementation Method 1
The AlGaN layer having the high Al composition is grown on an AlN substrate in a state of having the same lattice constant as the AlN substrate, in other words, in a pseudomorphic state
Implementation Method 2
since Fresnel reflection occurs at an interface between the AlN substrate and the n-type AlGaN layer, owing to the difference of a refractive index
Data Source
AI summary
An optical semiconductor element includes a single crystal AlN substrate; an n-type semiconductor layer having an AlGaN layer, the AlGaN layer being grown on the AlN substrate and being pseudomorphic with the AlN substrate, an Al composition of the AlGaN layer being reduced with an increase in distance from the AlN substrate; an active layer grown on the n-type semiconductor layer and having a multiple quantum well structure which includes a plurality of well layers and barrier layers; and a p-type semiconductor layer which is grown on the active layer. The single crystal AlN substrate has a dislocation density being 106 cm−2 or less.