Infrared Detector Pixel Structure for Low Crosstalk and Dark Current
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Solution Overview
Problem
Existing infrared detectors face challenges in achieving high quantum efficiency, minimizing crosstalk, and reducing dark current noise, particularly in the short-wave infrared (SWIR) and medium-wave infrared (MWIR) ranges at non-cryogenic temperatures.
Innovation Solution
The development of a pixel structure with a planar absorption structure that inverts heavy holes and light holes along the axis of the pixel, while avoiding interface dislocations, using semiconductor alloys with specific molar fractions and layer thicknesses to optimize quantum efficiency, reduce crosstalk, and minimize dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the diffusion length of minority charge carriers is increased to improve quantum efficiency, then more photons are converted to charge carriers, but crosstalk between adjacent pixels increases
Solution Approach 1:
The patent applies local quality by creating an asymmetric effective mass distribution within the absorbent region. Light holes are generated preferentially in the central zone where they contribute to the signal, while heavy holes are generated at the interfaces where they form depletion barriers. This spatial differentiation of charge carrier properties allows the structure to simultaneously achieve high quantum efficiency through extended carrier collection and low crosstalk through interface-confined heavy hole barriers.
2Measurement precision
If the absorbent region thickness is increased to improve quantum efficiency, then more incident photons are absorbed, but dark current noise increases
Solution Approach 1:
The patent employs parameter changes by modifying the effective mass parameter of charge carriers through compositional grading in the InGaAsSb alloy. By varying the indium and antimony content across the absorbent region thickness, the effective mass of holes is tuned to create an asymmetric distribution. This parameter modulation enables the structure to maintain low dark current while achieving high quantum efficiency through extended absorption depth.
3Measurement precision
If the effective mass of minority charge carriers is decreased to improve diffusion coefficient and quantum efficiency, then charge carrier mobility increases, but crosstalk between pixels increases due to increased diffusion length in the normal plane
Solution Approach 1:
The patent implements asymmetry by creating a directional effective mass distribution where light holes (low effective mass) are confined to the central absorbent region along the pixel axis, while heavy holes (high effective mass) are concentrated at the interfaces. This asymmetric spatial distribution of effective masses ensures high diffusion coefficients for signal generation in the vertical direction while suppressing lateral diffusion that causes crosstalk.
4Object-generated harmful factors
If the composition of semiconductor materials is optimized to reduce dark current, then intrinsic charge carrier density is reduced, but quantum efficiency decreases
Solution Approach 1:
The patent uses composite materials by combining multiple III-V semiconductor compounds (InGaAsSb) with graded composition throughout the absorbent region. This composite structure allows simultaneous optimization of dark current and quantum efficiency through spatially varying material properties. The compositional gradient creates the desired effective mass asymmetry while maintaining low intrinsic carrier density, achieving both low dark current and high quantum efficiency.
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 enhances the quantum efficiency of infrared detectors, reduces crosstalk between pixels, and minimizes dark current noise, thereby improving the overall performance of SWIR and MWIR detectors at non-cryogenic temperatures.
Implementation Method 1
photodiodes that transform a flux of incident photons into photogenerated charge carriers
Implementation Method 2
The quantum efficiency depends on the absorption coefficient and on the diffusion length Ldz in the structure of the pixel
Implementation Method 3
The diffusion length Ldz along the axis of the pixel increases with the diffusion coefficient along the axis of the pixel
Data Source
AI summary
A device for detecting infrared radiation, includes at least one pixel having an axis in a direction Z, the pixel comprising a first absorbent planar structure comprising at least one semiconductor layer. The composition of the materials used to produce the at least one layer of the first absorbent planar structure is chosen such that: the first absorbent planar structure has an effective valence band formed by a plurality of energy levels. Each energy level is occupied by one of: a first type of positive charge carrier, called heavy holes, having a first effective mass; or a second type of positive charge carrier, called light holes, having a second effective mass strictly less than the first effective mass. The maximum energy level of the effective valence band is occupied by light holes along the axis of the pixel.