Integrated VCSEL Photodiode Structure for Longer-Wavelength Sensing

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Solution Overview

Problem

Conventional Vertical Cavity Surface Emitting Lasers (VCSELs) based on the AlGaAs material system are limited to emitting laser light at wavelengths around 850 nm, which are visible to the human eye, and replacing the GaAs photodiode with an InGaAs-based one results in undesirable photodiode current behavior and increased capacitance.

Innovation Solution

A VCSEL device with a monolithically integrated photodiode using an InGaAs material system for both the active region and light absorption region, where the InGaAs layer in the light absorption region has a higher indium content than in the active region, to enable emission and detection in the 850 nm to 1200 nm wavelength range, reducing capacitance and voltage dependence of the photodiode current.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If GaAs photodiode is used in AlGaAs VCSEL, then device structure is simple and manufacturing is easy, but emission wavelength is limited to around 850 nm and cannot be extended to longer wavelengths

Engineering Contradiction:

Improveease of manufactureVSAvoidwavelength range

Core Design Contradiction:

Ease of manufactureVSAdaptability or versatility

Solution Approach 1:

The patent changes the material composition parameters by introducing InGaAs layers with varying indium content (x=0.02-0.15) in the light absorption region, while keeping the active region with lower indium content (y=0.02-0.05). This parameter change enables wavelength extension from 850 nm to 1200 nm while maintaining manufacturability through standard semiconductor fabrication processes.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs a composite material structure combining AlGaAs for the active region and InGaAs for the light absorption region. This composite approach leverages the advantages of both material systems: AlGaAs provides efficient lasing action while InGaAs enables extended wavelength detection, achieving both versatility and ease of manufacture.

Inventive Principle:

Principle #40Composite materials

2Adaptability or versatility

If InGaAs photodiode is used to extend wavelength range above 850 nm, then wavelength adaptability is improved, but photodiode current behavior becomes undesirable and capacitance increases

Engineering Contradiction:

Improvewavelength rangeVSAvoidphotodiode current behavior

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent applies local quality by creating different indium content regions: the active region has lower indium content (y=0.02-0.05) optimized for laser emission, while the light absorption region has higher indium content (x=0.02-0.15) optimized for wavelength extension. This spatial variation in material composition achieves wavelength adaptability while maintaining reliable photodiode current behavior through proper region differentiation.

Inventive Principle:

Principle #3Local quality

3Adaptability or versatility

If higher indium content InGaAs is used in light absorption region, then wavelength range above 850 nm is achieved and light absorption is improved, but device complexity increases

Engineering Contradiction:

Improvewavelength rangeVSAvoiddevice complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent segments the device into functionally distinct regions: the active region with lower indium content for laser emission and the light absorption region with higher indium content for wavelength extension. This segmentation allows each region to be optimized independently, achieving wavelength adaptability above 850 nm while managing device complexity through clear functional separation and standardized fabrication processes.

Inventive Principle:

Principle #1Segmentation

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

Enables laser light emission and detection in a longer wavelength range above 850 nm with improved light absorption and reduced capacitance, enhancing measurement accuracy in optical sensors.

Implementation Method 1

The InGaAs layer in the light absorption region has a higher indium content than in the active region, to enable emission and detection in the 850 nm to 1200 nm wavelength range

Methodology Applied

Scientific EffectLight absorption: Absorption (EM radiation)

Implementation Method 2

A VCSEL device with a monolithically integrated photodiode using an InGaAs material system for both the active region and light absorption region

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS12191630B2Vertical cavity surface emitting laser device with monolithically integrated photodiode

Publication Date: 2025.01.07 TRUMPF PHOTONIC COMPONENTS GMBH

AI summary

A vertical cavity surface emitting laser device includes: an optical resonator; a photodiode; and a contact arrangement. The optical resonator includes: two distributed Bragg reflectors (DBRs) and an active region between the DBRs. The photodiode has a light absorption region in the optical resonator. The contact arrangement provides drive current to pump the optical resonator, and contacts the photodiode. The active region has an InxGa1-xAs layer, where 0≤x<1. The light absorption region has an InyGa1-yAs layer, where 0<y<1, and y>x. The InyGa1-yAs layer is an intrinsic layer of the light absorption region. The InyGa1-yAs layer is 15-50 nm thick. The light absorption region has an undoped layer with a material different from the InyGa1-yAs layer. The InyGa1-yAs layer is immediately adjacent to the undoped layer. An intrinsic zone of the light absorption region is at least 70 nm thick.