Tunable VCSEL DBR Mirrors With Strain-Compensated Layer Compositions

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Solution Overview

Problem

Current semiconductor DBR mirrors in tunable VCSELs have limited refractive index contrast and spectral bandwidth, restricting their tuning range and reliability due to high cumulative strain and material strain limitations.

Innovation Solution

Expanding the material system for DBR mirrors by using InGaAs/AlGaAsP, InGaAsN/AlGaAsP, and AlGaAs/AlGaAsP compositions to achieve higher refractive index contrast and strain control, allowing for increased spectral reflection bandwidth and tuning range, with strain-balanced and lattice-matched layers reducing cumulative strain and defect formation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If GaAs/AlGaAs material system is used for DBR mirrors, then the device can be manufactured with standard processes, but the refractive index contrast is limited and spectral bandwidth is restricted

Engineering Contradiction:

ImprovemanufacturabilityVSAvoidspectral bandwidth

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent employs composite material structures by combining multiple semiconductor layers with different refractive indices (GaAs, AlGaAs, InGaAs, AlAsP, GaAlAsP) to create DBR mirrors with enhanced spectral bandwidth and refractive index contrast, while maintaining compatibility with standard semiconductor manufacturing processes

Inventive Principle:

Principle #40Composite materials

2Reliability

If the number of DBR mirror layers is increased to achieve higher reflectivity, then the spectral bandwidth improves, but cumulative strain increases causing defects and reducing reliability

Engineering Contradiction:

Improvespectral reflection bandwidthVSAvoidcumulative strain

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent changes material composition parameters by incorporating P-containing layers (AlAsP, GaAlAsP) with different lattice constants and strain characteristics to replace or supplement traditional AlGaAs layers, thereby reducing cumulative strain while maintaining or enhancing spectral bandwidth

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent applies local quality by strategically positioning strain-compensating layers at specific positions within the DBR structure, creating alternating regions of compressive and tensile strain that locally balance the cumulative strain across the multilayer structure

Inventive Principle:

Principle #3Local quality

3Reliability

If InGaAs layers are used to increase refractive index contrast, then DBR performance improves, but compressive strain increases requiring strain compensation

Engineering Contradiction:

Improverefractive index contrastVSAvoidcompressive strain

Core Design Contradiction:

ReliabilityVSStress or pressure

Solution Approach 1:

The patent applies counterweight by introducing P-containing layers (AlAsP, GaAlAsP) with tensile strain characteristics to balance and compensate for the compressive strain introduced by InGaAs high-index layers, achieving strain-balanced DBR structures

Inventive Principle:

Principle #8Anti-weight (Counterweight)

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 enhances the DBR mirror spectral reflection bandwidth and tunable VCSEL laser tuning range, improving device reliability and performance by increasing the number of H/L layer pairs without generating defects, and allowing for broader wavelength tuning.

Implementation Method 1

semiconductor distributed Bragg reflector (DBR) mirrors

Methodology Applied

Scientific EffectBragg diffraction: Bragg Diffraction

Implementation Method 2

distributed Bragg reflector (DBR) mirrors supporting tuning ranges

Methodology Applied

Scientific EffectInterference: Interference

Implementation Method 3

full control over the DBR structure strain either by balancing compressive and tensile strain of alternating mirror layers, or by using mirror layer materials lattice matched to the substrate

Methodology Applied

Scientific EffectStrain balancing:

Data Source

PatentEP4229725B1Tunable vcsel with strain compensated semiconductor dbr

Publication Date: 2024.08.07 EXCELITAS TECHNOLOGIES CORP

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AI summary

Tunable VCSELs (TVCSELs) employing expanded material systems with expanded mechanical/optical design space for semiconductor DBR mirrors on GaAs substrates. One is the InGaAs / AlGaAsP material system. It adds indium In to decrease InGaAs H-layer bandgap for higher refractive index and higher DBR layer refractive index contrast. Adding phosphorus P gives independent control of bandgap and strain of AlGaAsP low refractive index L-layers. The tensile strain of AlGaAsP L-layer compensates compressive strain of InGaAs H-layer and lowers the cumulative strain of the multilayer DBR structure. Another option is the InGaAsN(Sb) / AlGaAsP material system, where both types of layers can be lattice matched to GaAs. It uses indium In and nitrogen N, and possibly antimony Sb, to get independent control of strain and bandgap, and thus refractive index, of dilute nitride InGaAsN(Sb) H-layers, with lower bandgap and higher refractive index than starting GaAs. Using expanded material system enables reliable DBR mirrors with higher reflectivity and spectral bandwidth and tunable VCSELs with wider tuning range.