Al Composition Gradient in Nitride Semiconductor Lasers
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Solution Overview
Problem
Existing nitride-based semiconductor lasers with a ridge structure face challenges in achieving low device resistance due to non-uniform Mg incorporation and variations in superlattice structure formation, leading to difficulties in single transverse mode operation and high-temperature performance.
Innovation Solution
A group III nitride compound semiconductor light-emitting device with a current blocking layer having a striped aperture and a superlattice layer with a lower average Al composition ratio, buried inside the aperture, and a cladding layer with a higher Al composition ratio, which stabilizes low device resistance by reducing carrier resistance and maintaining optical confinement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a ridge structure is used with dry etching of the p-type cladding layer, then horizontal optical confinement is controlled by refractive-index difference, but variation in remaining thickness occurs and single transverse mode operation becomes difficult
Solution Approach 1:
The invention changes the Al composition ratio parameter to resolve the contradiction. The first AlGaN layer has a lower Al composition ratio (0.05-0.2) while the second AlGaN layer has a higher Al composition ratio (0.2-0.4). This parameter gradient allows the lower layer to provide good crystal growth conditions and the upper layer to provide strong optical confinement, achieving both manufacturing precision and operational reliability.
Solution Approach 2:
The invention uses a composite structure with two different AlGaN layers having different Al composition ratios. This composite approach combines the advantages of low-Al layers (better crystal growth, lower dislocation density) with high-Al layers (stronger optical confinement, better current blocking), resolving the contradiction between manufacturing precision and operational stability.
2Reliability
If the p-type cladding layer remaining thickness is increased to reduce refractive-index difference, then single transverse mode operation improves, but horizontal current broadening increases and operation current increases
Solution Approach 1:
The invention applies local quality by creating a gradient in Al composition ratio across the cladding layer structure. The lower layer with lower Al content allows better current confinement, while the upper layer with higher Al content provides optical confinement. This local differentiation allows thin layer design that reduces current broadening while maintaining single transverse mode operation.
Solution Approach 2:
By changing the Al composition ratio parameter across layers, the invention achieves effective current and optical confinement without increasing layer thickness. The higher Al content in the upper layer provides strong confinement properties, allowing thin overall structure that prevents current broadening while maintaining operational reliability.
3Ease of manufacture
If dry etching is used to form ridge waveguide, then processing is achieved, but variation in remaining thickness occurs and yield decreases
Solution Approach 1:
The invention changes from controlling thickness (prone to etching variation) to controlling Al composition ratio (precise via MOCVD). The composition ratio can be precisely controlled during crystal growth, avoiding the thickness variation problems inherent in dry etching processes, thereby improving yield while maintaining ease of manufacture.
Solution Approach 2:
The invention replaces the mechanical dry etching process with a crystal growth-based approach using MOCVD. Instead of mechanically removing material to define the waveguide, the desired structure is formed through controlled deposition with precise composition gradients, eliminating etching-induced thickness variation and improving manufacturing yield.
4Reliability
If outside the stripe is covered with nitride based material, then horizontal refractive-index difference is reduced and single transverse mode operation is achieved, but device resistance increases due to non-uniform Mg incorporation
Solution Approach 1:
The invention applies local quality by differentiating the Al composition ratio between layers. The lower layer with lower Al content provides better Mg incorporation uniformity and lower resistance, while the upper layer with higher Al content provides optical confinement. This spatial differentiation of composition resolves the contradiction between operational reliability and resistance uniformity.
Solution Approach 2:
The composite structure with two AlGaN layers of different compositions allows simultaneous achievement of optical confinement (from high-Al upper layer) and low uniform resistance (from low-Al lower layer). The composite approach combines the beneficial properties of different Al content regions to resolve the contradiction.
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 device achieves stable low device resistance and improved high-temperature and high-output performance by reducing refractive-index differences and carrier resistance, while maintaining optical confinement and beam shape control.
Implementation Method 1
horizontal refractive-index difference Δn is relatively low... single transverse mode operation with a high output can be easily realized
Implementation Method 2
outside the stripe is covered with a nitride based material having high coefficient of thermal conductivity, and therefore, radiation performance is high
Data Source
AI summary
A group III nitride compound semiconductor light-emitting device according to the present invention includes: an active layer (105) comprised of a group III nitride compound semiconductor; a current blocking layer (108) which is formed on the active layer (105) and has a striped aperture (108a); a superlattice layer (p-type layer 109) which buries the aperture (108a) and is comprised of a group III nitride compound semiconductor including Al; and a cladding layer (110) which is formed on the superlattice layer and is comprised of a group III nitride compound semiconductor including Al. When an average Al composition ratio of the superlattice layer is represented as x1 and an average Al composition ratio of the cladding layer (110) is represented as x2, it is represented as x1<x2.