Infrared Detection Element InAs Layer Thickness Optimization

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Solution Overview

Problem

Conventional infrared detection elements with an InAs intermediate layer and InAsSb upper and lower layers fail to improve element characteristics when the intermediate layer's thickness is set below a critical film thickness, as it leads to extended crystal defects and deteriorated crystallinity.

Innovation Solution

The infrared detection element incorporates a first InAsSb layer, an InAs layer grown on the first InAsSb layer, and a second InAsSb layer, where the InAs layer's thickness is set larger than its critical film thickness, preventing the growth of defects and improving crystallinity, especially when the As composition ratio is between 0.7 and 0.9, and the thickness is ≤ 2.0 µm for suitable mass production.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stress or pressure

If the thickness of the InAs intermediate layer is set to be less than or equal to the critical film thickness, then the stress on each layer is reduced, but the crystal defects extend from the interface and the crystallinity deteriorates

Engineering Contradiction:

Improvestress on layersVSAvoidcrystallinity

Core Design Contradiction:

Stress or pressureVSManufacturing precision

Solution Approach 1:

The patent inverts the conventional wisdom by setting the InAs layer thickness to be greater than the critical film thickness (hc < t ≤ 2.0 µm) rather than less than or equal to it. This counterintuitive approach allows defects to be confined to a limited region near the interface while maintaining excellent crystallinity in the bulk of the InAs layer and the InAsSb layers, thereby improving overall element characteristics.

Inventive Principle:

Principle #13The other way round (Inversion)

2Manufacturing precision

If the thickness of the InAs layer is set larger than the critical film thickness, then the crystallinity improves, but the manufacturing time increases considerably

Engineering Contradiction:

ImprovecrystallinityVSAvoidmanufacturing process time

Core Design Contradiction:

Manufacturing precisionVSLoss of time

Solution Approach 1:

The patent optimizes the InAs layer thickness parameter within a specific range (hc < t ≤ 2.0 µm), balancing crystallinity improvement with manufacturing efficiency. By setting an upper limit of 2.0 µm, the patent ensures that while the thickness exceeds the critical film thickness for defect suppression, the manufacturing process time remains acceptable for mass production.

Inventive Principle:

Principle #35Parameter changes

3Stress or pressure

If a superlattice structure is adopted in the intermediate layer, then the stress is distributed, but the defects extend from the interface and cannot be stopped in the thin InAs layer

Engineering Contradiction:

Improvestress distributionVSAvoiddefect growth

Core Design Contradiction:

Stress or pressureVSReliability

Solution Approach 1:

The patent extracts the superlattice structure from the intermediate layer configuration, adopting a simple single-layer InAs structure instead. This simplification, combined with optimizing the InAs layer thickness to be greater than the critical film thickness, effectively stops defect growth from the interface while maintaining stress management, thereby improving reliability.

Inventive Principle:

Principle #2Taking out (Extraction)

Data Source

PatentEP3067941B1Infrared detection element

Publication Date: 2018.05.23 HAMAMATSU PHOTONICS KK

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AI summary

This infrared detection element includes a buffer layer (InAsSb layer) 3, a buffer layer (InAs layer) 4, and a light absorption layer (InAsSb layer) 5. A critical film thickness hc of the InAs layer satisfies a relation of hc < t with a thickness t of the InAs layer. In this case, it is possible to improve crystallinities of the buffer layer 4 of InAs and the light absorption layer 5 of InAsSb formed on the buffer layer 3.