Bottom-Emitting Emitter Array Layout for Uniform Optical Power
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Solution Overview
Problem
Vertical-emitting devices, such as VCSELs, suffer from optical power non-uniformity due to long current paths between electrical contacts, leading to variations in bias current and optical power across the emitter array, which complicates accurate detection and sensing applications.
Innovation Solution
A bottom-emitting emitter array design with a metal layer on the substrate side, connected to the second electrical contact, featuring openings for light emission, reduces the lateral voltage gradient and optical power gradient by enabling lateral current flow through the metal layer, thereby improving optical power uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If electrical contacts are positioned at the top side of the epitaxial structure, then the device structure is simplified and manufacturing is easier, but long current paths cause optical power non-uniformity across the emitter array
Solution Approach 1:
The patent introduces a bottom-side metal layer on the substrate, creating a new dimensional pathway for current flow. This allows current to travel laterally through the substrate plane rather than vertically through long epitaxial paths, fundamentally changing the current transport dimension and achieving uniform bias distribution across the emitter array.
Solution Approach 2:
The bottom-side metal layer acts as an intermediary current distribution network between the top electrical contacts and the emitter array. It receives current from top contacts and redistributes it laterally across the substrate, mediating the current flow to eliminate voltage gradients and achieve uniform optical power output.
2Manufacturing precision
If the substrate size is increased to accommodate proper electrical contact spacing, then current distribution improves, but chip size increases which is not desirable
Solution Approach 1:
The invention utilizes the substrate plane (lateral dimension) as a current distribution pathway through the bottom metal layer. This allows effective current distribution across the emitter array without requiring increased vertical spacing or larger overall chip dimensions, as the lateral metal layer efficiently distributes current within the existing chip footprint.
Solution Approach 2:
The bottom-side metal layer serves dual functions: it provides mechanical support as part of the substrate structure and simultaneously acts as a current distribution network. This self-service approach eliminates the need for separate current distribution traces or larger contact spacing, maintaining compact chip size while achieving uniform current distribution.
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 design achieves improved optical power uniformity across the emitter array without increasing chip size, enhancing the accuracy of optical detection and sensing applications.
Implementation Method 1
a metal layer disposed on a bottom side of the substrate, where the metal layer is electrically connected to the second electrical contact
Implementation Method 2
the metal layer includes one or more openings for light emission of the plurality of bottom-emitting emitters
Data Source
AI summary
In some implementations, an emitter array may include a substrate, an epitaxial structure on the substrate, a plurality of bottom-emitting emitters defined in the epitaxial structure, a first electrical contact positioned at a top side of the epitaxial structure, a second electrical contact positioned at the top side of the epitaxial structure, and a metal layer disposed on a bottom side of the substrate. The metal layer may be electrically connected to the second electrical contact. The metal layer may include one or more openings for light emission of the plurality of bottom-emitting emitters.