InGaAs VCSEL Substrate Composition for Low-Absorption Back Emission
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Solution Overview
Problem
VCSEL devices using n-type GaAs or n-type InGaAs substrates face issues with light absorption and reduced light emission efficiency due to free carriers, and warping during production, especially in back-emitting devices.
Innovation Solution
Using an InxGa1-xAs substrate with a carrier concentration of less than 5×1017/cm3 and a lattice constant between GaAs and AlAs, combined with a specific DBR structure and electrode configuration, to minimize light absorption and warping, allowing for high light emission efficiency and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an n-type GaAs substrate or n-type InGaAs substrate is used in the back-emitting VCSEL device, then the substrate provides good lattice matching and electrical properties, but light absorption occurs due to free carriers and light emission efficiency is reduced
Solution Approach 1:
The patent changes the carrier concentration parameter of the substrate from typical values (10^18/cm³ or higher) to a low carrier concentration range (10^16/cm³ to 10^18/cm³). This parameter change reduces free carrier density, minimizing light absorption while maintaining electrical properties, thereby resolving the contradiction between reliability and light emission efficiency
Solution Approach 2:
The patent uses InxGa1-xAs substrate material with specific composition (x=0.005 to 0.015) that combines the advantages of GaAs (good lattice matching) with reduced free carrier effects. This composite approach creates a substrate that maintains electrical reliability while reducing light absorption losses
2Reliability
If AlGaAs DBR layers are used in the VCSEL device, then the DBR provides high reflectivity for laser oscillation, but warping occurs on the substrate during the production process
Solution Approach 1:
The patent changes the composition parameter x in InxGa1-xAs substrate (setting x=0.005 to 0.015) to adjust the lattice constant, making it intermediate between GaAs and AlAs. This parameter adjustment reduces lattice mismatch with AlGaAs DBR layers, minimizing thermal stress and warping during production while maintaining high DBR reflectivity
Solution Approach 2:
The patent applies local quality by creating a substrate with specific local composition characteristics (low x value in InxGa1-xAs) that optimizes lattice matching in the region where DBR layers are deposited, thereby reducing warping in the critical DBR formation area
3Loss of energy
If the substrate carrier concentration is reduced to minimize light absorption, then light emission efficiency improves, but substrate conductivity decreases
Solution Approach 1:
The patent optimizes the carrier concentration parameter to a specific range (10^16/cm³ to 10^18/cm³) that balances two competing requirements: low enough to minimize light absorption losses, but high enough to maintain adequate substrate conductivity for device operation and heat dissipation
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 solution enhances light emission efficiency and reduces crystal defects and warping, improving the reliability and productivity of VCSEL devices and arrays by suppressing light absorption and lattice distortion.
Implementation Method 1
when a laser beam is transmitted through the substrate, light absorption occurs due to free carriers of the n-type substrate and the light emission efficiency is reduced
Implementation Method 2
The pair of DBRs reflects light having a predetermined wavelength, of the spontaneous emission light, toward the active region, thereby generating laser oscillation
Implementation Method 3
an active region that is disposed between the first DBR and the second DBR and generates light emission due to carrier recombination
Implementation Method 4
it is important to reduce the warping on the substrate in the production process
Data Source
AI summary
[Object] To provide a vertical cavity surface emitting laser device and a vertical cavity surface emitting laser device array that use a GaAs substrate and have excellent light emission efficiency and reliability.[Solving Means] A vertical cavity surface emitting laser device according to the present technology includes: a substrate; and a light-emitting unit. The substrate is formed of InxGa1-xAs (x is 0.005 or more and 0.015 or less) and has a carrier concentration of less than 5×1017/cm3. The light-emitting unit includes a first distributed Bragg reflector (DBR) that is formed on the substrate and reflects light having a specific wavelength, a second DBR that reflects light having the wavelength, and an active region that is disposed between the first DBR and the second DBR and generates light emission due to carrier recombination.