Multi-section DBR VCSEL Aperture Oxidation Control
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Solution Overview
Problem
Existing oxide-confined vertical-cavity surface-emitting lasers (VCSELs) face degradation issues due to oxidation-induced defects and stress when the oxide-confined aperture is positioned close to the active medium, leading to non-radiative recombination and device degradation, and existing solutions fail to adequately control scattering loss and tapering effects.
Innovation Solution
A multi-section distributed Bragg reflector (DBR) structure is employed, with a high aluminum composition section forming the oxide-confined aperture, a low aluminum composition section to suppress vertical oxidation, and a moderately high aluminum composition section to prevent mesa-side oxidation, ensuring well-defined aperture thickness and reducing stress-induced defects, while a narrow band gap insertion traps minority carriers to prevent recombination at oxidation-induced defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the oxide-confined aperture is positioned close to the active medium, then the parasitic capacitance is reduced and high-speed operation is enabled, but oxidation-induced defects and stress cause non-radiative recombination and device degradation
Solution Approach 1:
The DBR layer is divided into multiple sections with different aluminum compositions: a first section (high Al content) to suppress oxidation from the mesa side, a second section (low Al content) to suppress vertical oxidation and reduce stress, and a third section (moderately high Al content) to maintain DBR functionality. This segmentation allows the aperture to be positioned close to the active medium while preventing oxidation-induced defects through the protective low-Al section.
Solution Approach 2:
Different sections of the DBR layer are assigned different aluminum compositions tailored to specific local requirements: the low-Al section is positioned where oxidation suppression and stress reduction are critical, while high-Al sections maintain optical reflectivity. This local quality differentiation enables the aperture to be placed close to the active medium without suffering from oxidation-induced reliability issues.
2Device complexity
If a single-layer DBR structure is used, then the device complexity is low, but scattering loss and tapering effects cannot be adequately controlled
Solution Approach 1:
The DBR layer is segmented into multiple sections with distinct aluminum compositions (first section: high Al, second section: low Al, third section: moderately high Al). This segmentation provides precise control over oxidation behavior and stress distribution, enabling accurate aperture thickness definition and reducing tapering effects, while the overall structure remains integrated within the DBR framework.
Solution Approach 2:
The DBR structure employs a composite of GaAlAs layers with varying aluminum compositions within a single layer. This composite approach allows different regions to exhibit different oxidation resistance and stress characteristics, enabling precise control of aperture formation while maintaining the structural integrity and optical functionality of the DBR.
3Speed
If the oxide-confined aperture is positioned close to the active medium, then the capacitance is reduced for high-speed operation, but stress accumulation and tapering effects increase
Solution Approach 1:
A low-aluminum composition section is strategically positioned adjacent to the oxide-confined aperture to provide a stress-relief zone and suppress vertical oxidation. This local quality modification stabilizes the aperture composition and reduces tapering effects, enabling the aperture to be positioned close to the active medium for high-speed operation without compromising compositional stability.
Solution Approach 2:
The low-Al section is positioned in advance to prevent stress accumulation and oxidation-induced tapering before they can affect the aperture. This preliminary protective action stabilizes the aperture composition, allowing high-speed operation with the aperture close to the active medium while maintaining compositional integrity.
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 reliable high-speed operation by preventing non-radiative recombination and device degradation, maintaining predictable aperture thickness and reducing optical scattering loss, thus enhancing the reliability and performance of VCSELs.
Implementation Method 1
the selective oxidation is possible, where one or several layers of AlAs or Ga(1−x)Al(x)As with a high Al content (preferably above 95%) is oxidized forming amorphous dielectric material AlO(y) or Ga(1−x)Al(x)O(y)
Implementation Method 2
a low aluminum composition in the second section suppresses non-desirable oxidation in the vertical direction of the layer adjacent to the targeted aperture layer
Implementation Method 3
A difference in aluminum composition between a high value in the aperture layer and a moderately high value in the first section suppresses non-desirable oxidation of the third section from the mesa side
Implementation Method 4
a narrow band gap insertion traps minority carriers to prevent recombination at oxidation-induced defects
Implementation Method 5
each DBR being composed of alternating layers having a high and a low refractive index
Data Source
AI summary
An oxide-confined vertical cavity surface emitting laser including a distributed Bragg reflector (DBR) wherein the layers of the (DBR) includes a multi-section layer consisting of a first section having a moderately high aluminum composition, an second section which is an insertion having a low aluminum composition, and a third section which is an oxide-confined aperture formed by partial oxidation of a layer having a high aluminum composition (95% and above). A difference in aluminum composition between a high value in the aperture layer and a moderately high value in the first section prevents non-desirable oxidation of the first section from the mesa side while the aperture layer is being oxidized. A low aluminum composition in the second section prevents non-desirable oxidation in the vertical direction of the layer adjacent to the targeted aperture layer.