VCSEL Mesa Shaping for Circular Oxide Apertures
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Solution Overview
Problem
VCSELs with anisotropic oxidation processes result in non-circular oxide apertures, leading to non-circular output beams, which deviate from the preferred circular beam profile due to differing oxidation rates across the x-y plane.
Innovation Solution
A method to determine the shape of the as-fabricated oxide aperture and calculate the necessary adjustments to the mesa structure to achieve a target aperture shape through etching, ensuring the mesa geometry compensates for anisotropic oxidation, thereby forming a desired aperture shape during the oxidation process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a circular mesa structure is used with anisotropic oxidation, then the fabrication process is simple, but the resulting oxide aperture becomes non-circular
Solution Approach 1:
The patent applies asymmetry by intentionally designing the mesa structure with a non-circular shape that compensates for the anisotropic oxidation rates. The mesa is shaped with different curvature radii in different directions (e.g., larger radius in the direction of faster oxidation, smaller radius in the direction of slower oxidation) so that after anisotropic oxidation, the resulting aperture becomes circular. This transforms the symmetric fabrication approach into an asymmetric design that achieves the desired symmetric outcome.
Solution Approach 2:
The patent implements preliminary anti-action by pre-compensating for the expected distortion caused by anisotropic oxidation. Before the oxidation process occurs, the mesa is deliberately shaped in a way that anticipates and counteracts the differential oxidation rates. The mesa geometry is calculated in advance to include the inverse of the expected distortion, so that when oxidation occurs, the final aperture shape is corrected to be circular.
2Productivity
If oxidation rates differ in x and y directions, then the oxidation process is faster in certain directions, but the aperture shape becomes non-circular
Solution Approach 1:
The patent applies local quality by varying the mesa geometry locally in different directions to compensate for local differences in oxidation rates. The mesa is designed with position-dependent curvature radii, where the curvature radius is adjusted at different angular positions around the mesa perimeter. This allows each local region of the mesa to be optimized for its specific oxidation rate, ensuring that faster-oxidizing regions have larger initial dimensions while slower-oxidizing regions have smaller initial dimensions, resulting in a uniform circular aperture.
3Shape
If the mesa shape is adjusted to compensate for anisotropic oxidation, then the aperture shape becomes circular, but the mesa fabrication becomes more complex
Solution Approach 1:
The patent applies parameter changes by modifying the geometric parameters of the mesa structure, specifically the curvature radius, to achieve the desired aperture shape. The mesa is defined by a curvature radius that varies as a function of the angular position around the mesa perimeter. This continuous parameter variation allows the mesa to compensate for anisotropic oxidation while maintaining a relatively simple fabrication process, as the varying curvature can be achieved through standard lithographic and etching techniques with appropriate mask design.
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 allows for the creation of oxide apertures of specific target shapes, such as circular, elliptical, or other geometries, ensuring consistent beam profiles even with anisotropic oxidation, thereby addressing the issue of non-circular apertures and beam profiles.
Implementation Method 1
the aperture is typically created by oxidizing the exposed mesa structure of a distributed Bragg reflector (DBR) portion of the VCSEL
Data Source
AI summary
A mesa structure for a VCSEL device is particularly configured to compensate for variations in the shape of the created oxide aperture that result from anisotropic oxidation. In particular, a suitable mesa shape is derived by determining the shape of an as-created aperture formed by oxidizing a circular mesa structure, and then ascertaining the compensation required to convert the as-created shape into a desired (“target”) shaped aperture opening. The compensation value is then used to modify the shape of the mesa itself such that a following anisotropic oxidation yields a target-shaped oxide aperture.