III-Nitride VCSEL Cavity Fabrication with ELO Wing DBR Mirrors
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Solution Overview
Problem
The fabrication of vertical cavity surface emitting lasers (VCSELs) faces challenges due to difficulties in creating distributed Bragg's reflectors (DBRs) for resonant cavities, particularly with III-nitride materials, where significant tensile strain between AlN and GaN hampers intuitive cavity design, leading to complex manufacturing procedures and yield issues.
Innovation Solution
The method employs hetero-epitaxy and substrate removal techniques using GaN-on-Si or GaN-on-Sapphire templates to grow high-crystalline quality III-nitride epitaxial layers, allowing for the placement of DBR mirrors on the wing regions of epitaxial lateral overgrowth (ELO) layers, which are then separated from the host substrate using laser lift-off or chemical etching, enabling the formation of curved mirrors to minimize electromagnetic field loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional VCSEL fabrication methods are used with III-nitride materials, then the device structure can be formed, but the significant tensile strain between AlN and GaN leads to complex manufacturing procedures and yield issues
Solution Approach 1:
The patent extracts and removes the problematic host substrate (sapphire or SiC) after growing the VCSEL device layers on it. This separation eliminates the source of tensile strain that causes cracking and yield issues, while allowing the device to be fabricated using conventional procedures without the harmful substrate constraints
Solution Approach 2:
The fabrication process is segmented into distinct stages: growing device layers on a sacrificial substrate, forming the complete VCSEL structure, then separating the device from the substrate. This segmentation allows each stage to be optimized independently, simplifying the overall manufacturing procedure while improving yield
2Loss of energy
If DBR mirrors are placed on flat substrate surfaces, then the resonant cavity can be formed, but electromagnetic field loss occurs; if curved mirrors are used instead, then field loss is minimized, but manufacturing becomes more difficult
Solution Approach 1:
The patent performs preliminary action by growing the DBR mirrors on the curved interface between the ELO mask and the III-nitride layers during the epitaxial growth process itself. This preliminary formation of curved mirrors eliminates the need for subsequent complex curved surface fabrication steps, making the manufacturing process easier while achieving the desired low field loss
Solution Approach 2:
The epitaxial growth process itself creates the curved mirror surface by utilizing the natural curvature at the ELO mask interface. The system serves itself by forming the curved geometry during standard layer growth without requiring additional specialized processing steps
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 results in high-yield, crack-free VCSELs with improved crystal quality and reduced dislocation density, facilitating easier device fabrication and integration, independent of substrate crystal orientation, and allowing for the creation of both short and long resonant cavities.
Implementation Method 1
ELO III-nitride layers are grown from opening areas on a substrate
Implementation Method 2
The host substrate may then be removed using laser lift-off
Implementation Method 3
chemical etching to separate the ELO III-nitride layers from the host substrate
Data Source
AI summary
Methods for fabricating a vertical cavity surface emitting laser (VCSEL) using epitaxial lateral overgrowth (ELO). The ELO layers comprise island-like III-nitride semiconductor layers grown on a substrate using a growth restrict mask, wherein the island-like III-nitride semiconductor layers comprise a light emitting resonant cavity. An aperture for the resonant cavity is fabricated on a wing of the ELO layers with distributed Bragg reflector (DBR) mirrors formed on bottom and top regions of the wing of the ELO layers.