Metallic Optical Cavity Enhances Light Extraction from Silicon Substrates

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Solution Overview

Problem

Conventional light emitting devices (LEDs) face challenges when integrated with high-index, absorbing materials like silicon due to light absorption and optical isolation requirements, leading to design complexity, increased cost, and reduced efficiency in emitting light into free space.

Innovation Solution

A light emitting device is designed with a semiconductor layer and a metallic structure, where a light emission layer comprising fluorescent molecules is confined between them, utilizing plasmonic modes to enhance light emission efficiency and reduce absorption by the substrate, thereby increasing external quantum efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If LEDs are formed directly on silicon substrate, then integration between electronic and optical circuits is achieved, but light absorption by silicon reduces optical efficiency

Engineering Contradiction:

Improveintegration of electronic and optical circuitsVSAvoidlight absorption by silicon

Core Design Contradiction:

Adaptability or versatilityVSLoss of energy

Solution Approach 1:

The device is segmented into distinct functional layers: an optical cavity layer containing the light emitter, a semiconductor layer for electrical contact, and a metallic layer for optical extraction. This segmentation allows each layer to be optimized for its specific function, enabling direct integration on silicon while minimizing light absorption losses through the engineered optical cavity structure.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

An optical cavity layer acts as an intermediary between the silicon substrate and the light emitter. This intermediate structure modifies the optical mode density and confines light within the cavity, preventing direct absorption by the silicon substrate while maintaining electrical connection through the semiconductor layer.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Loss of energy

If conventional optical isolation is used to prevent light absorption, then optical efficiency is maintained, but device complexity and manufacturing cost increase

Engineering Contradiction:

Improveoptical loss preventionVSAvoidoptical isolation structure

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The optical isolation function is merged with the electrical contact function through the semiconductor layer. The semiconductor layer simultaneously provides electrical connection to the light emitter and acts as part of the optical cavity structure, eliminating the need for separate optical isolation components and reducing device complexity.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The semiconductor layer serves multiple functions: it provides electrical contact to the light emitter, forms part of the optical cavity structure, and contributes to optical mode confinement. This multi-functionality reduces the number of separate components needed, simplifying the overall device structure while maintaining optical efficiency.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Reliability

If high-index materials are used for substrates, then electronic performance is optimized, but light emission into free space is reduced

Engineering Contradiction:

Improveelectronic performanceVSAvoidlight emission efficiency

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The device transitions from planar light emission to three-dimensional optical confinement within the cavity structure. By creating a vertically stacked configuration with the optical cavity, semiconductor, and metallic layers, light is confined in the vertical dimension while allowing efficient extraction in the lateral direction, overcoming the limitations of high-index substrates.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The optical properties of the device are optimized by carefully controlling the thickness and refractive index parameters of each layer. The optical cavity layer thickness and the metallic layer properties are specifically tuned to enhance light extraction efficiency, allowing the device to achieve high productivity despite using high-index silicon substrate.

Inventive Principle:

Principle #35Parameter changes

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 the external quantum efficiency of light emission into the far field, outperforming conventional materials and enabling bright, efficient visible-frequency optical sources on silicon substrates, which are otherwise optically isolated.

Implementation Method 1

confined between a semiconductor layer and a metallic structure, where the light emission layer is in physical contact with the metallic structure and the semiconductor layer

Methodology Applied

Scientific EffectPlasmonic modes:

Data Source

PatentUS10211428B2Metal-based optical device enabling efficient light generation from emitters on a high-index absorbing substrate

Publication Date: 2019.02.19 PRESIDENT & FELLOWS OF HARVARD COLLEGE

AI summary

A light emitting device is described that may reduce the coupling of emitted light into silicon and may increase the efficiency with which light is emitted into the far field. Such a device may include a semiconductor layer, a metallic structure, and a light emission layer disposed between the semiconductor layer and the metallic structure. The light emission layer may be in physical contact with the metallic structure and the semiconductor layer. The light emission layer may include at least one fluorescent molecule that emits light upon excitation.