VCSEL Structure With Tunnel Junction Aperture for Higher Bandwidth
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Solution Overview
Problem
Conventional VCSELs face limitations such as high free carrier absorption, uneven current injection, low modulation bandwidth, and poor thermal optimization due to the use of multi-layer P-type and N-type mirrors and a single oxidation limiting layer.
Innovation Solution
A new vertical cavity surface emitting laser structure is introduced, featuring a photoetched aperture structure of a second-class tunnel junction, an epitaxially grown upper N-type DBR, intra-cavity asymmetric electrodes of elliptical multi mesas, and a dielectric DBR with TiO2/Si3N4 materials, which improves current injection efficiency, heat dissipation, and modulation bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional multi-layer P-type and N-type mirrors are used, then the VCSEL structure is established, but free carrier absorption increases and current injection becomes uneven
Solution Approach 1:
The patent removes the P-type mirror layer from the conventional VCSEL structure, extracting the harmful P-type doped layer that causes free carrier absorption. The simplified structure uses only N-type DBR mirrors, eliminating the source of high free carrier absorption while maintaining the laser cavity functionality.
Solution Approach 2:
The patent changes the electrical parameters of the mirror structure by eliminating P-type doping and using only N-type doping with optimized doping concentrations (1×10^18 to 1×10^19 cm^-3). This parameter change reduces free carrier absorption and improves current injection uniformity across the active region.
2Reliability
If oxidation limiting layer is used for aperture definition, then the VCSEL structure is formed, but thermal optimization capability is limited and modulation bandwidth is reduced
Solution Approach 1:
The patent removes the oxidation limiting layer from the structure, extracting the component that limits thermal optimization. The aperture is defined by the N-type DBR mirror structure itself without requiring an additional oxidation layer, thereby eliminating the thermal barrier and enabling better heat dissipation.
Solution Approach 2:
The patent changes the aperture definition mechanism from oxidation-based to structure-based, where the aperture is determined by the lateral extent of the N-type DBR mirror and active region. This parameter change enables superior thermal optimization while achieving higher modulation bandwidths.
3Speed
If oxide aperture with diameter less than 3 microns is used to increase bandwidth, then modulation bandwidth increases, but manufacturing reliability and repeatability become challenging
Solution Approach 1:
The patent removes the oxidation process entirely from the manufacturing sequence, extracting the source of manufacturing variability. The aperture size is determined by the epitaxially grown N-type DBR mirror lateral dimensions, which can be precisely controlled during growth, eliminating the need for post-growth oxidation and improving manufacturing repeatability.
Solution Approach 2:
The patent performs aperture definition during the epitaxial growth stage itself, rather than as a subsequent oxidation step. The N-type DBR mirror is grown with the desired lateral dimensions that define the aperture, performing the aperture definition action in advance and ensuring consistent results without requiring precise oxidation control.
4Power
If conventional single layer N-type DBR is used, then the structure is simpler, but optical feedback efficiency and output power are limited
Solution Approach 1:
The patent uses composite N-type DBR mirror structures with alternating layers of different semiconductor materials (e.g., AlGaAs/GaAs or AlInGaAs/InGaAs) with different refractive indices. This composite structure enhances optical feedback efficiency through improved reflectivity while maintaining a manageable number of layers, thereby increasing output power.
Solution Approach 2:
The patent optimizes the DBR mirror parameters including the number of layers (5-15 pairs), layer thicknesses (quarter-wave optical thickness), and doping concentrations to achieve high reflectivity (>99%) and enhanced optical feedback efficiency, resulting in increased output power without excessive structural complexity.
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
The new structure enhances modulation bandwidth, current injection efficiency, reliability, heat dissipation, and output power, while optimizing the thermal and optical performance of the VCSEL.
Implementation Method 1
a photoetched aperture structure of a second-class tunnel junction
Implementation Method 2
epitaxially growing an upper N-type distributed Bragg reflector (DBR)
Implementation Method 3
intra-cavity asymmetric electrodes of elliptical multi mesas
Implementation Method 4
a dielectric DBR with few logarithm after photoetching the second-class tunnel junction into an elliptical aperture
Data Source
AI summary
Provided are a new vertical cavity surface emitting laser structure and a manufacturing method thereof. The structure includes a substrate layer, a lower N-type DBR, an active region, an upper N-type DBR and a mixed dielectric DBR sequentially arranged from bottom to top, where a second-class tunnel junction is arranged on one side of the active region close to the upper N-type DBR, where the second-class tunnel junction is embedded in a bottom of the upper N-type DBR and surrounded by the upper N-type DBR, and the substrate layer, the lower N-type DBR, the active region, the upper N-type DBR, the mixed dielectric DBR and the second-class tunnel junction are all coaxial elliptical cylinders; negative electrodes are arranged on the lower N-type DBR, and positive electrodes are arranged on the upper N-type DBRs substrate layer.