Nitride Semiconductor Laser Tilted Epitaxial Substrate
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Solution Overview
Problem
Nitride semiconductor lasers face challenges in reducing driving voltage while maintaining optical confinement, as existing designs often require graded composition in p-type cladding layers to achieve strain and conductivity, which can lead to increased absorption loss and mobility issues.
Innovation Solution
The design incorporates a p-type cladding region with two distinct group III nitride semiconductor layers, where the first layer has an AlGaN layer with anisotropic strain and a larger band gap, and the second layer has lower resistivity, allowing for superior optical confinement and reduced driving voltage without graded composition, and an epitaxial substrate with a tilted primary surface to enhance strain and conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single p-type AlGaN cladding layer with high Al composition is used to provide electron barrier, then the optical confinement is improved, but the strain in the layer increases leading to potential relaxation and reduced reliability
Solution Approach 1:
The p-type cladding region is divided into multiple distinct layers: a first p-type AlGaN layer with high Al composition (20-30%) for providing electron barrier and optical confinement, and a second p-type AlGaN layer with lower Al composition (5-15%) for reducing strain and improving hole transport. This segmentation allows each layer to be optimized for its specific function, resolving the contradiction between optical confinement and strain management.
Solution Approach 2:
Different regions of the cladding structure are assigned different material compositions tailored to local requirements. The first cladding layer near the active region has high Al content for electron blocking and optical confinement, while the second cladding layer has lower Al content for strain relief and improved electrical properties. This local quality differentiation enables simultaneous optimization of optical and electrical performance without compromising reliability.
2Reliability
If graded composition is used in the p-type cladding layer to manage strain, then the strain relaxation is prevented, but the absorption loss increases and mobility decreases
Solution Approach 1:
Instead of using a continuous graded composition transition, the patent employs discrete step-function composition changes between distinct layers. The first p-type AlGaN layer maintains constant high Al composition for optimal electron barrier properties, and the second layer maintains constant lower Al composition for strain management. This segmentation eliminates the absorption losses associated with graded interfaces while still preventing strain relaxation through the compositional step change.
3Reliability
If the p-type cladding layer has high Al composition for electron barrier, then the optical confinement is improved, but the resistivity increases leading to higher driving voltage
Solution Approach 1:
The cladding structure is segmented into a first layer optimized for electron barrier function with high Al composition and a second layer optimized for electrical conductivity with lower Al composition. The second layer acts as a transport layer that facilitates hole injection while the first layer maintains the electron barrier and optical confinement functions. This segmentation resolves the contradiction by separating the electron barrier function from the electrical transport function into different layers.
Solution Approach 2:
Different compositional qualities are assigned to different parts of the cladding structure based on local functional requirements. The region adjacent to the active layer uses high Al content for electron blocking, while the outer region uses lower Al content for improved hole transport and reduced resistivity. This local quality optimization enables the device to achieve both low driving voltage and effective electron confinement.
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 configuration reduces the forward driving voltage by lowering the dynamic electrical resistance and maintaining excellent optical confinement, while preventing strain relaxation in the AlGaN layer, thus improving the overall performance of the nitride semiconductor laser.
Implementation Method 1
the AlGaN layer includes anisotropic strain; a band gap of the AlGaN layer of the first p-type group III nitride semiconductor layer is largest at the p-type cladding region
Implementation Method 2
The primary surface is tilted with respect to a reference plane; the reference plane is perpendicular to a reference axis; the reference axis extends in a direction of a c-axis of the gallium nitride based semiconductor
Data Source
AI summary
A nitride semiconductor laser comprises a conductive support base having a primary surface of gallium nitride based semiconductor, an active layer on the primary surface, and a p-type cladding region on the primary surface. The primary surface is tilted to a reference plane perpendicular to a reference axis extending in the c-axis direction of the gallium nitride based semiconductor. The p-type cladding region comprises a first p-type group III nitride semiconductor layer of an AlGaN layer anisotropically-strained, and a second p-type group III nitride semiconductor layer of material different from the AlGaN layer. The first p-type group III nitride semiconductor layer is provided between the second p-type group III nitride semiconductor layer and the active layer. The AlGaN layer has the largest bandgap in the p-type cladding region. The second p-type group III nitride semiconductor layer has a resistivity lower than the first p-type group III nitride semiconductor layer.