Angled Semiconductor Nano-pillars for Grazing Angle Absorption

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Solution Overview

Problem

Optical absorption elements with nano-pillars are limited in their ability to absorb light efficiently over a broad bandwidth and are sensitive to incident angle and polarization, with significant reflection occurring near the grazing angle, especially when nano-pillars are configured perpendicular to the normal.

Innovation Solution

The development of an optical absorption element featuring an array of angled, conical-shaped nano-pillars made of semiconductor materials, which are fabricated using techniques like electron beam lithography and reactive ion dry etching to create angular asymmetry, enhancing absorption by directing nano-pillars at a specific angle relative to the normal, thereby improving absorption over a wider bandwidth.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If nano-pillars are configured perpendicular to the normal, then the structure is simple and symmetric, but absorption efficiency deteriorates at grazing angles due to increased reflection

Engineering Contradiction:

Improvestructural simplicityVSAvoidreflection loss at grazing angles

Core Design Contradiction:

Ease of operationVSLoss of energy

Solution Approach 1:

The patent applies asymmetry by tilting the nano-pillars at a specific angle (e.g., 45 degrees) relative to the normal of the substrate surface. This asymmetric configuration creates angular selectivity in the absorption characteristics, enabling the structure to absorb radiation more effectively at specific incident angles while reducing reflection losses that occur with perpendicular configurations.

Inventive Principle:

Principle #4Asymmetry

2Ease of manufacture

If conventional materials are used, then the material is easy to manufacture, but reflection increases as the angle of incidence approaches the grazing angle

Engineering Contradiction:

Improvematerial availabilityVSAvoidreflection at grazing angles

Core Design Contradiction:

Ease of manufactureVSLoss of energy

Solution Approach 1:

The patent changes the geometric parameters of the nano-structure by tilting the nano-pillars at a specific angle relative to the normal. This parameter change modifies the interaction between incident radiation and the material surface, reducing Fresnel reflection at grazing angles while maintaining the use of conventional semiconductor materials that are easy to manufacture.

Inventive Principle:

Principle #35Parameter changes

3Loss of energy

If cylindrical nano-posts are used, then absorption is enhanced through coupling into azimuthal waveguide modes, but the structure remains sensitive to incident angle and polarization

Engineering Contradiction:

Improveabsorption efficiencyVSAvoidangular and polarization insensitivity

Core Design Contradiction:

Loss of energyVSAdaptability or versatility

Solution Approach 1:

The patent introduces asymmetry by tilting the cylindrical nano-pillars, which modifies the coupling conditions for waveguide modes. This asymmetric configuration creates angular selectivity that enhances absorption at specific incident angles while reducing the sensitivity to polarization, thereby improving adaptability to different radiation conditions.

Inventive Principle:

Principle #4Asymmetry

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 configuration significantly enhances radiation absorption across a broad bandwidth, particularly in a specific direction, while reducing noise from other angles, demonstrating improved performance compared to traditional perpendicular nano-pillar configurations.

Implementation Method 1

enhanced absorption of radiation due to strong coupling into the first order azimuthal waveguide modes of the individual nano-structures

Methodology Applied

Scientific EffectWaveguide modes coupling: Waveguide (optics)

Implementation Method 2

the reflection characteristic of a material is primarily due to the Fresnel conditions that describe the behavior of light when moving between media having different indexes of refraction

Methodology Applied

Scientific EffectFresnel reflection: Fresnel Diffraction

Implementation Method 3

Silicon nano-pillars exhibit unique optical behavior at small scales, such as field enhancement on their surfaces

Methodology Applied

Scientific EffectField enhancement:

Implementation Method 4

employ a self-assembly process where monolayers of polystyrene nano-spheres (PSNSs) are coated with SiO2 by oblique evaporation at a deposition angle of 70°

Methodology Applied

Scientific EffectOblique evaporation: Physical Vapour Deposition

Data Source

PatentUS10935702B2Reflection and diffraction control with slanted semiconductor metamaterials

Publication Date: 2021.03.02 NORTHROP GRUMMAN SYSTEMS CORP

AI summary

An absorption element for absorbing radiation incident on the element at a certain wavelength band. The element includes a surface defining a normal direction perpendicular to the surface. The element also includes an array of a plurality of spaced apart nano-pillars extending from the surface at an angle orientation other than the normal direction, which creates angular asymmetry so as to increase the element's absorption response in a particular direction. The nano-pillars are made of a suitable semiconductor material and have a size relative to the wavelength band to absorb the radiation. In one non-limiting embodiment, the nano-pillars are angled at 45° relative to the normal direction and are cone-shaped to broaden their absorption capabilities.