Bonded Dielectric-DBR VCSEL Structure for Flip-Chip Coupling
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Solution Overview
Problem
The emission direction of most vertical cavity surface emitting lasers (VCSELs) is away from the substrate due to the opaque substrate, making it difficult to couple the laser in flip chip packaging, which complicates the semiconductor process and limits integration with other materials.
Innovation Solution
A novel VCSEL structure using dielectric layers to form distributed Bragg reflectors instead of semiconductor layers, integrated through bonding technology, allowing for reduced epitaxy time and the replacement of opaque substrates with infrared transparent materials, enabling wafer-level integration with Si photonic chips.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an opaque substrate is used in VCSEL, then the substrate provides mechanical support and structural stability, but the laser emission direction is forced away from the substrate making it difficult to couple the laser in flip chip packaging
Solution Approach 1:
The VCSEL structure is divided into two separate substrates: a first substrate carrying the dielectric DBR and a second substrate (GaAs) carrying the active region and arsenide DBR. These are bonded together through bonding layers, allowing the GaAs substrate to be removed later. This segmentation enables the laser to emit toward the dielectric DBR side without requiring the opaque GaAs substrate to be present during operation, thus resolving the coupling difficulty while maintaining structural stability during fabrication.
Solution Approach 2:
Bonding layers are introduced as intermediary elements between the first substrate (dielectric DBR) and the second substrate (GaAs substrate with active region). These bonding layers facilitate the temporary attachment of substrates during fabrication, enable the removal of the GaAs substrate, and allow the laser to emit toward the dielectric DBR side in the final structure, solving the emission direction problem.
2Reliability
If semiconductor layers are used to form distributed Bragg reflectors in VCSEL, then the reflectors provide necessary optical reflection, but the epitaxy process time is excessively long
Solution Approach 1:
The patent replaces the conventional semiconductor-based distributed Bragg reflector (formed through lengthy epitaxial growth) with a dielectric-based DBR structure. The dielectric DBR is fabricated separately on the first substrate using deposition techniques rather than epitaxy, significantly reducing the epitaxial growth time required for the active region while maintaining the necessary optical reflection performance through the dielectric layer stack.
3Reliability
If the GaAs substrate is retained in the final VCSEL structure, then the substrate provides mechanical support, but it prevents wafer level integration with Si photonic chips due to material incompatibility
Solution Approach 1:
The GaAs substrate is separated from the final VCSEL structure through the bonding layer architecture. The second substrate (GaAs) with the active region is temporarily attached to the first substrate, then removed after the active region is formed. This allows the final device to be mounted on a Si photonic chip substrate without the GaAs substrate present, enabling wafer-level integration while maintaining the mechanical support function during critical fabrication steps.
Solution Approach 2:
The bonding layers serve as intermediary elements that enable the temporary use of GaAs substrate during epitaxial growth, then allow its removal. This intermediary approach provides the mechanical support needed during fabrication while eliminating the material incompatibility issue for final integration with Si photonic chips.
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 reduces epitaxy process time, facilitates integration with Si photonic chips, and allows for adjustable laser emission direction, improving manufacturing efficiency and reliability.
Implementation Method 1
distributed Bragg reflector (DBR) on both upper and lower sides of the active region. The reflector is formed by interleaved semiconductor layers, which is quarter wavelength thick at the wavelength (in the medium) of interest
Implementation Method 2
The reflector is formed by interleaved semiconductor layers, which is quarter wavelength thick at the wavelength (in the medium) of interest. By controlling the growth of epitaxial materials, one can adjust the reflectivity of DBRs to make the cavity resonance happened in the vertical direction
Implementation Method 3
a second bonding layer is deposited to cover the heavily doped layer and the surface is prepared for van der Waals direct bonding; after the first substrate and the third substrate are bonded by combining bonding layers on each side together
Implementation Method 4
By controlling the growth of epitaxial materials, one can adjust the reflectivity of DBRs; a second substrate that has been epitaxially grown with a etch-stop layer, a heavily doped layer, an active region consists of cladding layers and multi-quantum wells
Implementation Method 5
the second substrate is then removed by wafer thinning and wet etching process and stopped on the etch-stop layer, which also will be etched completely to expose the heavily doped layer
Data Source
AI summary
A method of fabricating vertical cavity surface emitting laser, comprising: providing a first substrate formed with a dielectric DBR and a first bonding layer, and a second substrate formed with a etch-stop layer, a heavily doped layer, an active region, a current-confinement layer, and an arsenide DBR firstly, then sticking a third substrate on the arsenide DBR, then removing the second substrate and the etch-stop layer, next bonding the heavily doped layer to the dielectric DBR, next removing the third substrate, finally forming a p-type electrode contact and an n-type electrode contact.