VCSEL Array With Undoped Bottom Mirror And Trench Metallization
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Solution Overview
Problem
High power VCSEL array designs face challenges in achieving homogeneous carrier injection while maintaining high efficiency, as the use of a highly conductive substrate and doped bottom DBR leads to increased laser light absorption, reducing efficiency.
Innovation Solution
A top-emitting VCSEL array with undoped semiconductor mirrors between the active region and the substrate, where trenches or holes are formed between the bottom semiconductor mirrors and the upper substrate layer for metallization to enable homogeneous carrier injection without increasing light absorption, using a doped upper substrate layer for electrical conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a doped bottom DBR is used for homogeneous carrier injection, then electrical conductivity is improved, but laser light absorption increases reducing efficiency
Solution Approach 1:
The patent divides the electrical connection path into two segments: the undoped bottom DBR remains optically transparent while trenches are created to provide separate electrical connection paths through metallization layers. This segmentation allows the optical path to remain undoped for efficiency while electrical injection occurs through alternative pathways via the trenches and metallization structures.
Solution Approach 2:
The patent introduces metallization layers and trenches as intermediary structures between the substrate and the active region. These intermediaries provide the necessary electrical conductivity for carrier injection without requiring the bottom DBR itself to be doped, thus maintaining optical transparency while enabling electrical function through intermediate conductive elements.
2Loss of energy
If an undoped bottom DBR is used to minimize light absorption, then efficiency is improved, but homogeneous carrier injection becomes difficult
Solution Approach 1:
The patent transitions from vertical electrical injection through the doped bottom DBR to lateral electrical injection through trenches filled with metallization. By changing the dimension of current flow from vertical (through the DBR) to lateral (through trenches at the interface), the system maintains an undoped bottom DBR for optical efficiency while achieving homogeneous carrier injection through the alternative dimensional pathway.
Solution Approach 2:
The patent segments the electrical injection function from the optical mirror function by creating separate structural elements: the undoped bottom DBR handles optical reflection while trenches with metallization handle electrical injection. This functional segmentation resolves the contradiction by allowing each component to optimize for its primary function without compromising the other.
3Reliability
If a highly conductive substrate and doped bottom DBR are used for carrier injection, then homogeneous current distribution is achieved, but VCSEL efficiency decreases due to increased absorption
Solution Approach 1:
The patent segments the electrical connection system into multiple components: the highly conductive substrate remains for mechanical support and initial current distribution, while trenches with metallization layers provide the critical injection paths through the undoped bottom DBR region. This segmentation allows current distribution to occur through the substrate and metallization network without requiring the bottom DBR to be doped, thus maintaining efficiency while achieving homogeneous current distribution.
Solution Approach 2:
The metallization layers in the trenches act as intermediaries that bridge the highly conductive substrate to the active region, enabling homogeneous current distribution without passing current through the bottom DBR. This intermediary structure allows the substrate to provide its conductive benefits while the undoped bottom DBR maintains its optical transparency.
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 allows for homogeneous carrier injection and high power density while minimizing light absorption, resulting in a high-efficiency VCSEL array.
Implementation Method 1
A metallization (i.e. metal contacts or a metal layer) electrically connects the upper layer of the substrate with the current injection layer through said trenches and/or holes
Implementation Method 2
Doped DBRs show a higher absorption of the generated laser light than undoped DBRs. Therefore, for high efficient VCSEL designs the use of undoped DBRs is preferred
Implementation Method 3
each VCSEL being formed of at least a top mirror, an active region, a current injection layer and an undoped bottom semiconductor mirror
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
The present invention relates to a VCSEL array comprising several VCSELs arranged side by side on a common substrate (1). Each VCSEL is formed of at least a top mirror (5, 14), an active region (4), a current injection layer (3) and an undoped bottom semiconductor mirror (2). The current injection layer (3) is arranged between the active region (4) and the bottom semiconductor mirror (2). At least an upper layer of the substrate (1) is electrically conducting. Trenches (8) and/or holes are formed between the bottom semiconductor mirrors (2) of said VCSELs to said upper layer of said substrate (1). A metallization (9) electrically connects the upper layer of the substrate (1) with the current injection layer (3) through said trenches (8) and/or holes. The proposed VCSEL array allows a homogeneous current injection an has a high efficiency and power density.