Graded Multilayer Absorber for Infrared Detectors

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Infrared radiation detectors using single homogenous semiconductor layers, such as HgCdTe, require substantial cooling to reduce noise and dark current at high temperatures, limiting their operational temperature and increasing cooling system size and cost.

Innovation Solution

A radiation detector with a photodiode featuring a graded multilayer absorber structure, where each layer has a varying bandgap, allowing carriers to drift to a thin, narrow bandgap layer, reducing dark current and enabling higher operating temperatures without performance degradation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a single homogenous semiconductor layer is used, then the detector structure is simple, but dark current increases and noise increases at high temperatures

Engineering Contradiction:

Improveabsorber structureVSAvoiddark current

Core Design Contradiction:

Device complexityVSObject-generated harmful factors

Solution Approach 1:

The absorber is divided into multiple layers with different bandgap energies. The first absorber layer has a first bandgap energy and the second absorber layer has a second bandgap energy that is greater than the first bandgap energy. This segmentation allows each layer to be optimized for specific wavelength ranges while controlling dark current generation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the absorber are given different properties through varying bandgap energies. The first absorber layer with lower bandgap is positioned to absorb longer wavelengths, while the second absorber layer with higher bandgap handles shorter wavelengths. This local differentiation optimizes both quantum efficiency and dark current suppression in each region.

Inventive Principle:

Principle #3Local quality

2Object-generated harmful factors

If cooling is increased to reduce dark current, then dark current decreases, but power consumption increases and cooling system size increases

Engineering Contradiction:

Improvedark currentVSAvoidcooling power

Core Design Contradiction:

Object-generated harmful factorsVSUse of energy by stationary object

Solution Approach 1:

The bandgap energy parameter is changed across different absorber layers to optimize performance. By having the second absorber layer with a greater bandgap energy than the first layer, the structure inherently suppresses thermal generation of carriers, reducing dark current without requiring excessive cooling power.

Inventive Principle:

Principle #35Parameter changes

3Ease of manufacture

If a single homogenous semiconductor layer is used, then manufacturing is simple, but wavelength range coverage is limited

Engineering Contradiction:

Improveabsorber fabricationVSAvoidwavelength range

Core Design Contradiction:

Ease of manufactureVSAdaptability or versatility

Solution Approach 1:

The absorber is segmented into multiple layers, each with different bandgap energies tailored to specific wavelength ranges. This allows the detector to cover a broader spectral range while maintaining manufacturing feasibility through sequential layer deposition.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The absorber uses a composite structure with multiple semiconductor layers having different compositions and bandgap energies. This composite approach enables coverage of extended wavelength ranges while maintaining compatibility with standard semiconductor fabrication processes.

Inventive Principle:

Principle #40Composite materials

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 graded multilayer absorber structure reduces dark current density and noise equivalent flux, allowing the detector to operate at higher temperatures with reduced cooling needs, leading to smaller and less costly imaging systems.

Implementation Method 1

A radiation detector with a photodiode featuring a graded multilayer absorber structure, where each layer has a varying bandgap, allowing carriers to drift to a thin, narrow bandgap layer

Methodology Applied

Scientific EffectBandgap engineering:

Implementation Method 2

allowing carriers to drift to a thin, narrow bandgap layer

Methodology Applied

Scientific EffectCarrier drift:

Implementation Method 3

Photodiodes have been configured in many ways and use many different materials for absorbing light energy over different wavelengths to generate photocurrent or voltage

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS9209346B2Radiation detector having a bandgap engineered absorber

Publication Date: 2015.12.08 DRS NETWORK & IMAGING SYSTEMS LLC

AI summary

A radiation detector is provided that includes a photodiode having a radiation absorber with a graded multilayer structure. Each layer of the absorber is formed from a semiconductor material, such as HgCdTe. A first of the layers is formed to have a first predetermined wavelength cutoff. A second of the layers is disposed over the first layer and beneath the first surface of the absorber through which radiation is received. The second layer has a graded composition structure of the semiconductor material such that the wavelength cutoff of the second layer varies from a second predetermined wavelength cutoff to the first predetermined wavelength cutoff such that the second layer has a progressively smaller bandgap than the first bandgap of the first layer. The graded multilayer radiation absorber structure enables carriers to flow toward a conductor that is used for measuring the radiation being sensed by the radiation absorber.