Semiconductor Laser Ridge Design for Mode Suppression
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Solution Overview
Problem
In semiconductor lasers with quantum dot active layers, the convex shape of the n-type clad layer formed by wet etching leads to a trapezoidal ridge portion, causing higher modes to mix with oscillated light and increasing contact resistance between the clad layer and electrode, hindering high-speed modulation.
Innovation Solution
A semiconductor laser design with a first conductive type lower clad layer, a quantum dot active layer, and an isolated ridge portion in the second conductive type upper clad layer, where the width of the top of the ridge portion is equal to or greater than the bottom, achieved by dry-etching the second layer and wet-etching the first layer, to prevent higher modes from mixing with oscillated light and reduce contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the ridge portion is formed by wet etching to reduce the bottom width, then higher modes are suppressed, but the top width is reduced increasing contact resistance
Solution Approach 1:
The n-type clad layer is divided into two layers with different Al compositional ratios, where the first layer (higher Al ratio) is wet-etched to form the ridge portion with suppressed higher modes, and the second layer (lower Al ratio) maintains adequate top width for low contact resistance. This segmentation allows each layer to fulfill different functional requirements.
Solution Approach 2:
Different regions of the n-type clad layer are given different Al compositional ratios to optimize local properties. The first layer has higher Al ratio for effective higher mode suppression through wet etching, while the second layer has lower Al ratio to maintain good electrical contact with the electrode. This local quality differentiation resolves the contradiction between mode suppression and contact resistance.
2Manufacturing precision
If the bottom width of the ridge portion is reduced to suppress higher modes, then optical confinement is improved, but the top width is also reduced increasing contact resistance
Solution Approach 1:
The n-type clad layer is segmented into two layers with different compositions. The first layer is wet-etched to create the ridge portion with controlled bottom width for optimal optical confinement, while the second layer extends to provide adequate top width for low contact resistance. This segmentation decouples the conflicting requirements of optical confinement and electrical contact.
Solution Approach 2:
The ridge portion structure is made asymmetric through the two-layer configuration, where the first layer forms a narrower ridge for optical confinement while the second layer provides a wider top surface for electrical contact. This asymmetric design allows the structure to optimize both optical and electrical performance simultaneously.
3Ease of manufacture
If the ridge portion has a trapezoidal shape from wet etching, then fabrication is simple, but higher modes mix into oscillated light
Solution Approach 1:
The n-type clad layer is segmented into two layers where the first layer is wet-etched to form the ridge portion. The specific Al compositional ratio in the first layer controls the etching rate to create an optimized profile that suppresses higher modes while maintaining fabrication simplicity. This segmentation allows wet etching to be used effectively without the harmful trapezoidal shape effects.
Solution Approach 2:
The Al compositional ratio parameter is changed between the two layers to achieve different etching rates. The first layer has higher Al ratio for selective wet etching that creates the desired ridge profile for mode suppression, while the second layer has lower Al ratio to maintain structural integrity and electrical properties. This parameter change enables improved mode purity while keeping the wet etching process.
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 effectively suppresses higher modes and enhances high-speed modulation by maintaining a steep side surface of the upper clad layer and preventing over-etching of the active layer, thereby improving optical confinement and reducing contact resistance.
Implementation Method 1
achieved by dry-etching the second layer and wet-etching the first layer
Implementation Method 2
achieved by dry-etching the second layer and wet-etching the first layer
Data Source
AI summary
The present invention provides a semiconductor laser including a first conductive type of a lower clad layer 12, an active layer 14 provided on the lower clad layer 12, the active layer 14 including a plurality of quantum dots, and a second conductive type of an upper clad layer 18, the upper clad layer 18 being provided on the active layer 14 so as to have an isolated ridge portion 30 such that W1≦Wtop+0.4 μm where Wtop is the width of a top of the ridge portion 30 and W1 is the width of the ridge portion 30 at a height of 50 nm from a bottom of the ridge portion 30. The present invention also provides a method for manufacturing such a semiconductor laser.