Metal Oxide UVLED Epitaxy on 4H-SiC for Higher UVC Output
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Solution Overview
Problem
Existing ultraviolet light emitting devices (UVLEDs) based on Group-III-Nitrides face efficiency and output power limitations due to low crystallographic structure quality caused by lattice mismatch with sapphire substrates, particularly in the UVC wavelength band.
Innovation Solution
The development of an optoelectronic semiconductor light emitting device using a substrate with epitaxial semiconductor layers composed of metal oxides, such as (AlxGa1-x)2O3, which supports an optical emission region with a band structure capable of emitting light in the range of 150 nm to 425 nm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If sapphire substrates are used to grow Group-III-Nitride layers, then UVLED devices can be manufactured, but the crystallographic structure quality deteriorates due to large lattice mismatch
Solution Approach 1:
The patent introduces an intermediate buffer layer structure between the sapphire substrate and the Group-III-Nitride active layers. This buffer layer acts as a mediator that gradually transitions the lattice mismatch, reducing dislocation density and improving crystal quality while still enabling manufacture on sapphire substrates
Solution Approach 2:
The patent employs composite material structures including multiple epitaxial layers with different compositions (AlN, GaN, AlGaN) stacked in specific sequences. This composite approach allows optimization of each layer's properties to manage lattice mismatch and improve overall crystal quality
2Adaptability or versatility
If AlN layers are used to extend wavelength range to shorter wavelengths, then UVC operation below 280 nm is achieved, but output optical power dramatically declines
Solution Approach 1:
The patent applies local quality by using different material compositions in different regions of the device structure. AlN-rich compositions are used where short wavelength emission is needed, while GaN-rich compositions are used in regions where higher output power is required, optimizing both wavelength range and power output
Solution Approach 2:
The patent implements dynamic compositional grading in the epitaxial layers, where the aluminum content is gradually varied to transition between different bandgap energies. This dynamic composition profile allows tuning of emission wavelength while maintaining acceptable output power across a broad spectrum
3Adaptability or versatility
If heterojunction p-i-n diodes are used for UVLED structure, then UVC wavelength generation is achieved, but efficiency is limited by defect density
Solution Approach 1:
The patent performs preliminary actions by growing high-quality buffer layers and transition layers before depositing the active regions. This preliminary structuring minimizes defect propagation to the active layers, reducing non-radiative recombination and improving overall conversion efficiency
Solution Approach 2:
The patent introduces intermediate transition layers between the heterojunction regions that act as mediators to reduce defect density. These intermediate layers with graded compositions minimize dislocation propagation and improve carrier recombination efficiency
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 enhances the efficiency and output optical power of UVLEDs by improving the crystal quality of the metal oxide layers, thereby extending the wavelength range and increasing the emission efficacy.
Implementation Method 1
Electro-optical conversion of electrical energy into discrete optical wavelengths with extremely high efficiency has generally been achieved using a tailor-made semiconductor having the required properties to achieve the spatial recombination of charge carriers of electrons and holes to emit light of the required wavelength
Data Source
AI summary
The techniques described herein relate to a semiconductor structure including: a substrate, or a single crystal growth surface, including single crystal 4H-SiC(0001); a buffer layer on the single crystal growth surface; and an epitaxial oxide layer on the buffer layer. The buffer layer can include a crystal symmetry type that is compatible with the single crystal 4H-SiC(0001). The epitaxial oxide layer can include single crystal (AlxGa1-x)2O3 with a monoclinic or corundum crystal symmetry, and where 0≤x≤1.