Nanocolumn LED Heterostructure with Self-Centered Passivation

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Solution Overview

Problem

Nanocolumn-based LEDs face issues with reduced active region area due to parasitic pathways on non-polar facets, inefficient emission spectrum, and dislocations, particularly in core-shell structures, which affect light output efficiency and spectral purity, especially for high-frequency applications like displays.

Innovation Solution

A semiconductor heterostructure with a self-centered passivation disc on top of nanocolumns to prevent current injection into unwanted facets, forcing quantum well growth only along target facets, and using a top-down approach to achieve higher nanostructure densities and reduce dislocations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If core-shell nanocolumns are used to increase active region area, then light output efficiency is improved, but parasitic pathways on semi-polar facets cause current by-pass and reduce effectiveness

Engineering Contradiction:

Improvelight output efficiencyVSAvoidparasitic current pathways

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The patent extracts and removes the harmful semi-polar facets from the nanocolumn structure through selective etching processes. This eliminates the parasitic current pathways that were causing efficiency losses, while preserving the beneficial non-polar facets for light emission.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent converts the naturally formed semi-polar facets, which were causing harm through parasitic current pathways, into a beneficial process feature by using controlled etching to selectively remove them. The etching process itself becomes the mechanism to eliminate the harmful effect.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Area of stationary object

If nanocolumns are over-grown to form GaN-InGaN core-shell heterostructures, then active region area increases, but quantum well thickness becomes non-uniform across different facets

Engineering Contradiction:

Improveactive region areaVSAvoidquantum well thickness uniformity

Core Design Contradiction:

Area of stationary objectVSManufacturing precision

Solution Approach 1:

The patent applies local quality by creating different surface properties on different facets of the nanocolumn. The non-polar facets are prepared to receive uniform quantum well deposits, while the semi-polar facets are selectively removed. This ensures that the quantum well layer is deposited only on the desired facets with controlled, uniform thickness.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent performs preliminary selective etching of semi-polar facets before quantum well deposition. This preliminary action prepares the surface by removing unwanted facets and exposing only the non-polar facets, ensuring that subsequent quantum well growth occurs uniformly on the correct surfaces.

Inventive Principle:

Principle #10Preliminary action

3Adaptability or versatility

If different facets incorporate indium differently during InGaN shell growth, then emission spectrum becomes multi-banded, but spectral purity is reduced

Engineering Contradiction:

Improveemission spectrum coverageVSAvoidspectral purity

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

The patent extracts and removes the semi-polar facets that were causing multi-banded emission. By eliminating these facets through selective etching, only the non-polar facets remain to emit light, resulting in a single, pure emission band at the desired wavelength.

Inventive Principle:

Principle #2Taking out (Extraction)

4Reliability

If nanocolumns are grown on non-native substrates, then crystalline quality is improved, but active region area is reduced compared to flat analogues

Engineering Contradiction:

Improvecrystalline qualityVSAvoidactive region area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent transitions from a two-dimensional flat structure to a three-dimensional nanocolumn array structure. This dimensional change allows the active region to extend vertically along the nanocolumn height while maintaining high crystalline quality, effectively increasing the total active region area beyond what is possible with flat analogues.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The patent uses curved nanocolumn surfaces with specific crystallographic orientations (non-polar facets) to achieve both high crystalline quality and increased active region area. The cylindrical geometry allows for extended growth in the vertical dimension while maintaining favorable surface properties for carrier injection and light emission.

Inventive Principle:

Principle #14Spheroidality (Curvature)

Data Source

PatentUS20230207730A1Semiconductor heterostructure

Publication Date: 2023.06.29 UNIV COLLEGE CORK NAT UNIV OF IRELAND CORK

AI summary

A semiconductor heterostructure device for use as a component in an optoelectronic component, the device has a substrate, a nanocolumn extending from the substrate, a self-centred passivation layer on top of the nanocolumn, an active region which comprises a quantum well (QW) stack on a vertical side of the nanocolumn and wherein the passivation layer extends horizontally outwards from the nanocolumn to overhang the nanocolumn and the QW stack. The device provides for efficient NC heterostructure based light emitting diodes (LEDs) and other optoelectronic devices with an active region located purely on non-polar facets of the NCs. It also eliminates parasitic current paths allowing core-shell nanorod-based LEDs with emission from the desired facets only.