Modulation Doped AlGaN Heterostructure for UV LED Reliability
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Solution Overview
Problem
Achieving high p-type conductivity in magnesium (Mg)-doped aluminum gallium nitride (AlGaN) is challenging due to high acceptor activation energy and low hole mobility, leading to degradation in ultraviolet light emitting diodes (UV LEDs) caused by nitrogen vacancy formation and hole trapping in semiconductor layers.
Innovation Solution
A heterostructure design with a p-type contact layer and an electron blocking layer, where the p-type dopant concentration in the electron blocking layer is at most ten percent of the p-type contact layer concentration, combined with modulation doping and optimization of compositional and strain profiles, to reduce defect formation and enhance device reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If heavy Mg doping is used to increase p-type conductivity, then carrier concentration increases, but acceptor activation energy increases and hole mobility decreases
Solution Approach 1:
An undoped AlGaN layer is introduced as an intermediary between the n-type AlGaN layer and the p-type AlGaN layer. This intermediary layer reduces the formation of nitrogen vacancies and defects at the heterostructure interfaces, thereby improving device reliability while maintaining the high carrier concentration achieved through heavy Mg doping in the p-type layer.
Solution Approach 2:
The patent optimizes the aluminum molar fraction and thickness of the undoped AlGaN layer to balance between reducing defect formation and maintaining electrical performance. By carefully controlling these parameters, the patent achieves both high carrier concentration and improved device reliability.
2Illumination intensity
If high aluminum molar fraction is used in AlGaN layers, then bandgap increases for UV emission, but acceptor activation energy increases and unintentional donor concentration increases
Solution Approach 1:
The patent employs local quality by using different aluminum molar fractions in different layers: high aluminum content in the n-type and undoped layers for UV emission, while maintaining moderate aluminum content in the p-type layer to ensure adequate p-type conductivity. The undoped layer acts as a buffer to mitigate the negative effects of high aluminum content on acceptor activation.
3Productivity
If electrons with high kinetic energy cross the p-n junction, then carrier injection efficiency improves, but nitrogen vacancy formation increases
Solution Approach 1:
The undoped AlGaN layer is positioned preliminarily between the n-type and p-type layers to preemptively reduce the formation of nitrogen vacancies before high-energy electrons can cause damage at the heterostructure interfaces. This preliminary protective layer mitigates the harmful effects of high-energy electron impact while allowing efficient carrier injection to proceed.
Data Source
AI summary
An improved heterostructure for an optoelectronic device is provided. The heterostructure includes an active region, an electron blocking layer, and a p-type contact layer. The p-type contact layer and electron blocking layer can be doped with a p-type dopant. The dopant concentration for the electron blocking layer can be at most ten percent the dopant concentration of the p-type contact layer. A method of designing such a heterostructure is also described.