Dual-band infrared detector array with segmented mesas
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Solution Overview
Problem
Existing dual-band infrared detectors face challenges in achieving simultaneous detection of two wavelength bands without spatial offset, require complex read-out circuits, and are limited by large pixel size and high dark-current noise at elevated temperatures due to thick absorber layers and separate PN diodes.
Innovation Solution
The implementation of two carrier-selective barriers that allow uni-directional flow of electrons and holes, enabling simultaneous dual-band detection with aligned light-absorbing regions and reduced absorber volume, which minimizes depletion regions and dark current, and uses metal-filled via holes and pyramidal features for efficient light trapping and absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If two back-to-back photodiodes are stacked directly above each other in the same mesa for dual-band detection, then simultaneous detection of two wavelength bands is enabled, but spatial offset between images occurs when the platform or object moves rapidly
Solution Approach 1:
The detector structure is segmented into three separate mesas instead of stacking absorbers in a single mesa. Each mesa is laterally offset from the others, allowing independent optimization of each band's detection region while maintaining simultaneous detection capability. This segmentation resolves the spatial alignment issue by providing physically separated but optically aligned detection paths.
Solution Approach 2:
The invention transitions from a vertical stacking approach (single mesa with stacked absorbers) to a lateral arrangement approach (multiple mesas arranged in the lateral dimension). By distributing the two light-absorbing regions across multiple mesas in the lateral dimension rather than stacking them vertically, the patent achieves simultaneous detection without spatial offset while maintaining compact form factor.
2Measurement precision
If three separate mesas are used to provide simultaneous dual-band output with aligned absorbers, then spatial alignment is improved, but pixel size becomes large (50 μm or larger)
Solution Approach 1:
The patent nests the light-absorbing regions within a shared common mesa structure, with two additional mesas positioned adjacent to it. The common mesa contains both light-absorbing regions in a compact vertical arrangement, while the additional mesas provide electrical access. This nested configuration allows small pixel pitch by consolidating the optical function in a compact volume rather than spreading it laterally.
Solution Approach 2:
The invention merges the two light-absorbing regions into a single common mesa structure rather than using three completely separate mesas. This consolidation allows the two absorbers to share the same lateral footprint, dramatically reducing pixel size while maintaining spatial alignment. The electrical contacts are then routed to provide separate outputs for each band from this compact merged structure.
3Productivity
If thick absorber layers are used in dual-band detectors, then absorption efficiency is improved, but dark-current noise increases at elevated temperatures
Solution Approach 1:
The thick absorber is segmented into two separate light-absorbing regions with different thicknesses optimized for different wavelength bands. The first light-absorbing region is thinner and optimized for shorter wavelengths, while the second region is thicker and optimized for longer wavelengths. This segmentation allows each region to have minimal thickness necessary for its band, reducing overall dark current while maintaining absorption efficiency for both bands.
Solution Approach 2:
The patent applies local quality by having different absorber thicknesses in different regions of the detector. The first light-absorbing region has a thickness optimized for shorter wavelengths (thinner), while the second light-absorbing region has a thickness optimized for longer wavelengths (thicker). This localized optimization allows each region to achieve sufficient absorption efficiency with minimal thickness, thereby reducing dark-current noise at elevated temperatures.
4Productivity
If separate PN diodes are used for each wavelength band, then simultaneous dual-band detection is enabled, but device complexity and read-out circuit requirements increase
Solution Approach 1:
The common mesa serves multiple functions: it contains both light-absorbing regions, provides electrical contacts for both bands, and acts as the substrate for the entire structure. The first additional mesa and second additional mesa also serve multiple functions, providing electrical access while maintaining mechanical support. This multi-functionality reduces the number of separate components needed, simplifying the overall device structure and read-out circuit requirements.
Solution Approach 2:
The invention merges the electrical contact structures for the two bands into a unified mesa architecture. Rather than requiring completely separate read-out circuits for each band, the shared common mesa allows both light-absorbing regions to be electrically accessed through a unified contact structure. This merging of electrical paths simplifies the read-out circuit design while maintaining the ability to separately detect both wavelength bands.
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 solution enables compact, high-efficiency dual-band detectors with aligned images, reduced noise, and operation at higher temperatures, facilitating large-format imagers with smaller pixel pitch and lower noise performance.
Implementation Method 1
a first light-absorbing region of a first light-absorbing material configured to absorb incident light in a shorter-wavelength band to produce photo-carriers
Implementation Method 2
a second light-absorbing region of a second light-absorbing material configured to absorb incident light in a longer-wavelength band to produce photo-carriers
Implementation Method 3
a first carrier-selective barrier disposed between the first light-absorbing region and the second light-absorbing region that selectively blocks flow of holes through the first light-absorbing region but that permits flow of electrons through the first light-absorbing region
Implementation Method 4
a second carrier-selective barrier disposed between the second light-absorbing region and the collector layer that selectively blocks flow of electrons through the second light-absorbing region but that permits flow of holes through the second light-absorbing region
Implementation Method 5
uses metal-filled via holes and pyramidal features for efficient light trapping and absorption
Data Source
AI summary
An infrared photo-detector array and a method for manufacturing it are disclosed. The infrared photo-detector array contains a collector layer, a first absorber layer that absorbs incident light of a first wavelength band and generates first electrons and first holes, a second absorber layer that absorbs incident light of a second wavelength band and generates second electrons and second holes, and wherein the wavelengths of the incident light in the first wavelength band are shorter than the wavelengths of the incident light in the second wavelength band, and wherein the second absorber layer is laterally contiguous across at least two photo-detectors. The method disclosed teaches how to manufacture the infrared photo-detector array.