ZnO LED Structure for High-Temperature Operation
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Solution Overview
Problem
Current light-emitting diodes (LEDs) used in high optical power applications suffer from reduced efficiency at elevated temperatures due to heat extraction and dissipation difficulties, leading to thermionic emission and non-radiative recombination, which necessitates additional cooling and increases manufacturing and operating costs.
Innovation Solution
A semiconductor light-emitting diode structure utilizing n-type conductivity zinc oxide (ZnO) or cadmium zinc oxide (CdZnO) layers with a strained p-AlGaN/p-GaN heterostructure, incorporating a hole accumulation layer to reduce parasitic resistance and enable efficient excitonic transitions up to 400°C without additional cooling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional GaN/InGaN quantum well LEDs are used for high optical power applications, then light emission capability is achieved, but efficiency is dramatically reduced at elevated temperatures due to thermionic emission and non-radiative recombination
Solution Approach 1:
The patent changes the material composition parameter by replacing conventional GaN/InGaN quantum wells with ZnO-based active layers. ZnO has a wider bandgap (3.37 eV) and higher excitonic binding energy (60 meV) compared to GaN, which fundamentally alters the temperature dependence of radiative recombination. This material parameter change enables efficient light emission at temperatures up to 400°C without the thermionic emission losses that plague conventional LEDs.
Solution Approach 2:
The patent employs a composite heterostructure consisting of ZnO active layers combined with AlGaN cladding layers and SiC substrates. This composite material system leverages the high excitonic binding energy of ZnO for efficient radiative recombination at high temperatures, while AlGaN provides structural stability and lattice matching, and SiC offers superior thermal conductivity for heat dissipation. The synergistic combination of these materials resolves the temperature-efficiency contradiction.
2Power
If large emitting area LED structures are used for high optical power output, then light emission intensity is improved, but heat extraction and dissipation become difficult leading to efficiency degradation
Solution Approach 1:
The patent enables the LED structure to self-manage heat through the intrinsic high thermal conductivity of the SiC substrate and the high excitonic binding energy of ZnO. The ZnO-based active layer maintains radiative efficiency at high temperatures without requiring external cooling systems, and the SiC substrate passively conducts heat away from the active region. This self-service approach eliminates the need for additional cooling infrastructure while maintaining high optical power output.
3Use of energy by moving object
If additional cooling systems are added to maintain LED efficiency at elevated temperatures, then operational efficiency is maintained, but manufacturing and operating costs increase
Solution Approach 1:
The patent extracts and eliminates the need for external cooling systems by incorporating high-temperature resilient materials directly into the LED structure. The ZnO-based active layer with its 60 meV excitonic binding energy inherently resists thermal dissociation of excitons up to 400°C, and the SiC substrate provides passive thermal management. This extraction of the cooling system requirement simplifies device complexity while maintaining radiative efficiency.
4Temperature
If ZnO-based materials are used to enable high temperature operation, then cooling requirements are eliminated, but internal resistance and radiative efficiency need optimization
Solution Approach 1:
The patent applies local quality optimization by creating a heterostructure where different layers have specialized functions: ZnO active layers provide high-temperature radiative recombination, AlGaN cladding layers provide carrier confinement and structural stability, and SiC substrates provide thermal management. The AlGaN/ZnO heterojunction creates a type-II band alignment that locally optimizes carrier injection and confinement at the interface, enhancing radiative efficiency. This localized optimization of material properties at different positions within the device achieves both high temperature operation and maintained radiative 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
The ZnO/AlGaN-based LED structure maintains high radiative efficiency and reduces internal resistance at elevated temperatures, allowing for efficient light emission in the blue and ultraviolet spectral ranges, suitable for general purpose lighting without the need for additional cooling.
Implementation Method 1
The optical mechanism of transition in the ZnO active region of LEDs is annihilation of excitons. The high excitonic binding energy is expected to prevent thermal dissociation of excitons at temperatures as high as 400° C., thereby leading to the design and fabrication of solid state optical light emitters operating at fairly high temperatures without additional cooling.
Implementation Method 2
A semiconductor light-emitting diode structure utilizing n-type conductivity zinc oxide (ZnO) or cadmium zinc oxide (CdZnO) layers with a strained p-AlGaN/p-GaN heterostructure
Data Source
AI summary
A heterostructure semiconductor device capable of emitting electromagnetic radiation and having a junction with opposite conductivity type materials on either side thereof supported on a substrate with an active layer therebetween comprising zinc oxide and having a band gap energy that is less than that of either of the opposite conductivity type materials.