Red Light VCSEL Graded Mirror Thermal Management
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Solution Overview
Problem
Red light emitting Vertical Cavity Surface Emitting Lasers (VCSELs) face limitations in temperature range and maximum output power, particularly for shorter wavelengths, due to small bandgap discontinuities and low thermal conductivities in AlGaInP-AlGaAs material systems, leading to increased carrier escape and heating issues.
Innovation Solution
The VCSEL design incorporates a compound semiconductor substrate with graded constituent concentration mirror pairs, stressed quantum wells, and optimized doping and layer thicknesses to minimize electrical resistance and enhance thermal conductivity, along with proton implantation for current confinement and improved thermal management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If AlGaInP-AlGaAs material system is used for red light VCSELs, then emission wavelength and visible light capability are improved, but thermal conductivity and bandgap discontinuity are reduced leading to heating issues and carrier escape
Solution Approach 1:
The patent modifies the material composition parameters by incorporating indium into the AlGaAs mirror layers to create AlGaInP material system. This changes the bandgap and thermal properties while maintaining the quarter-wave optical thickness for red light emission, thereby improving visible light capability while managing thermal conductivity through compositional adjustment
Solution Approach 2:
The patent uses composite AlGaInP-AlGaAs material structure where AlGaInP active region with quantum wells is combined with AlGaAs mirror structures. This composite approach allows optimization of each layer for its specific function: AlGaInP for light emission at 660nm with appropriate bandgap, and AlGaAs for high reflectivity mirrors with better thermal conductivity, resolving the thermal management contradiction
2Illumination intensity
If AlGaInP-AlGaAs material system is used for red light VCSELs, then emission wavelength is improved, but maximum output power is limited due to small bandgap discontinuities and low thermal conductivity
Solution Approach 1:
The patent adjusts the indium composition ratio in AlGaInP layers to optimize the bandgap discontinuity at quantum well interfaces. By controlling the indium content, the patent enhances carrier confinement in quantum wells while maintaining lattice matching, thereby increasing maximum output power without sacrificing emission wavelength precision
Solution Approach 2:
The patent applies different material compositions and doping levels to different regions: AlGaInP with specific In content for active region to maximize carrier confinement and light emission, AlGaAs for mirrors to provide high reflectivity and thermal conduction, and graded buffer layers to manage dislocation density. This local optimization resolves the contradiction between emission wavelength and maximum output power
3Ease of manufacture
If standard VCSEL structure is used, then manufacturing simplicity is maintained, but temperature range and output power are limited
Solution Approach 1:
The patent segments the VCSEL structure into distinct functional layers with optimized compositions: AlGaInP active region with quantum wells for light emission, AlGaAs mirror pairs for optical feedback, graded buffer layers for dislocation management, and contact layers for electrical connection. This segmentation allows each layer to be optimized for its specific function while maintaining overall manufacturing feasibility through sequential epitaxial growth
Solution Approach 2:
The patent modifies key structural parameters including layer thicknesses (quarter-wave optical thickness for mirrors), indium composition ratios in AlGaInP layers, and doping concentrations in contact layers. These parameter changes enhance temperature range and output power while preserving the fundamental VCSEL manufacturing process through modified chemical vapor deposition or molecular beam epitaxy
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 enhances the temperature range and output power of red light VCSELs, particularly for shorter wavelengths, by reducing carrier escape and heating, while allowing for larger single mode aperture sizes and improved reliability.
Implementation Method 1
The injected carriers are captured by these quantum wells and then combine to thereby emit light
Implementation Method 2
The mirrors, 2 and 3, forming the optical resonance cavity are constructed from AlGaAs materials
Implementation Method 3
Many periods (>20) of alternating quarter wavelength thick layers of these two materials forms a highly reflective mirror at the intended emission wavelength
Implementation Method 4
each first mirror pair separated from that one remaining by a first mirror spacer layer with a graded constituent concentration
Implementation Method 5
The quantum well structures can be under stress in one direction with the active region spacer layer under stress in an opposite direction
Implementation Method 6
proton implantation for current confinement and improved thermal management
Implementation Method 7
optimized doping and layer thicknesses to minimize electrical resistance and enhance thermal conductivity
Implementation Method 8
enhance thermal conductivity, along with proton implantation for current confinement and improved thermal management
Data Source
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AI summary
A semiconductor material vertical cavity surface emitting laser for emitting narrow linewidth light comprising a compound semiconductor material substrate and pairs of semiconductor material layers in a first mirror structure on the substrate of a first conductivity type each differing from that other in at least on constituent concentration and each first mirror pair separate from that one remaining by a first mirror spacer layer with a graded constituent concentration. An active region on the first mirror structure has plural quantum well structures separated by at least one active region spacer layer and there is a second mirror structure on the active region similar to the first but of a second conductivity type. A pair of electrical interconnections is separated by said substrate, said first mirror structure, said active region and said second mirror structure.