Nanowire LEDs on Graphitic Substrates for UV Extraction
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Solution Overview
Problem
Current UV LEDs, particularly those based on AlGaN, AlInGaN, and AlN thin films, face challenges such as low external quantum efficiency, difficulty in growing high-quality films on conventional substrates, and absorption of UV light by substrates, limiting their performance in emitting deep UV light effectively.
Innovation Solution
The growth of AlN/AlGaN/AlInGaN nanowires or nanopyramids on graphitic substrates like graphene, which acts as both a substrate and a transparent conductive contact, enhancing light extraction efficiency and carrier injection efficiency through strategic doping and superlattice structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional substrates like sapphire or silicon are used for UV LED growth, then nanowire growth can occur, but the substrates absorb UV light and reduce light extraction efficiency
Solution Approach 1:
The patent extracts the graphitic layer from its conventional role as only a substrate, giving it dual functionality as both substrate and transparent conductive contact. This extraction of the harmful absorption property from the optical path while maintaining substrate functionality resolves the contradiction between enabling nanowire growth and preventing UV light absorption.
Solution Approach 2:
The graphitic layer serves multiple functions simultaneously: it acts as the substrate for nanowire growth, provides electrical contact, and maintains transparency to UV light. This multi-functionality eliminates the need for separate components that would otherwise be required, thereby improving light extraction efficiency while enabling device operation.
2Illumination intensity
If AlGaN, AlInGaN, or AlN thin films are used for UV emission, then deep UV wavelengths can be achieved, but external quantum efficiency remains very low (1-6%)
Solution Approach 1:
The patent transitions from planar thin film structures to vertically oriented nanowire structures. This dimensional change enables improved carrier confinement and reduced defect density, thereby achieving higher external quantum efficiency while maintaining the capability to emit deep UV wavelengths through appropriate material composition.
Solution Approach 2:
The device employs composite structures combining different group III-nitride materials (AlGaN, AlInGaN, AlN) with graphitic layers. This composite approach allows optimization of both the emission wavelength through material composition and the efficiency through the unique properties of the graphitic contact layer, resolving the trade-off between wavelength and efficiency.
3Illumination intensity
If group III-nitride semiconductor thin films are used, then UV emission can be achieved, but high-quality film growth on conventional substrates is difficult
Solution Approach 1:
The graphitic layer serves as an intermediary between the conventional substrate and the group III-nitride nanowires. It provides a suitable growth interface that enables high-quality nanowire formation while allowing the use of conventional substrates, thereby resolving the manufacturing difficulty without sacrificing emission quality.
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 approach improves the external quantum efficiency of UV LEDs by reducing light absorption and achieving higher hole injection efficiency, enabling more effective emission of deep UV light with improved homogeneity and efficiency.
Implementation Method 1
a thin graphitic layer as a transparent substrate for the growth of nanowires or nanopyramids which can be formed into LEDs and photodetectors e.g. for the emission or detection of light in the visible or UV spectrum
Implementation Method 2
nanowires or nanopyramids having a p-n or p-i-n junction... light is preferably emitted in a direction substantially parallel to but opposite from the growth direction of the nanowires
Implementation Method 3
a second electrode in contact with the top of at least a portion of said nanowires or nanopyramids optionally in the form of a light reflective layer
Data Source
AI summary
A light emitting diode device comprising: a plurality of nanowires or nanopyramids grown on a graphitic substrate, said nanowires or nanopyramids having a p-n or p-i-n junction, a first electrode in electrical contact with said graphitic substrate; a light reflective layer in contact with the top of at least a portion of said nanowires or nanopyramids, said light reflective layer optionally acting as a second electrode; optionally a second electrode in electrical contact with the top of at least a portion of said nanowires or nanopyramids, said second electrode being essential where said light reflective layer does not act as an electrode; wherein said nanowires or nanopyramids comprise at least one group III-V compound semiconductor; and wherein in use light is emitted from said device in a direction substantially opposite to said light reflective layer.