Modulation Doped GaN Heterostructure for UV LED Defect Reduction
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Solution Overview
Problem
Achieving high p-type conductivity in gallium nitride (GaN) and aluminum gallium nitride (AlGaN) layers for electronic and optoelectronic devices is challenging due to high acceptor activation energy and low hole mobility, leading to defects and degradation in ultraviolet light emitting diodes (UV LEDs).
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, along with modulation doping and optimization of compositional and doping profiles, strains, and polarization fields to reduce defect formation and enhance reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heavy Mg doping is used to achieve high p-type conductivity, then the conductivity increases, but the reliability deteriorates due to defect formation and degradation
Solution Approach 1:
The patent applies local quality by creating distinct regions with different doping concentrations - a heavily doped contact layer for conductivity and a lightly doped or undoped electron blocking layer for reliability. This spatial variation in doping quality allows each region to optimize its function without compromising the other.
Solution Approach 2:
The p-type layer is segmented into multiple functional regions: a contact layer with high Mg doping concentration (1e19 to 1e21 atoms/cm³) and an electron blocking layer with low or zero Mg doping. This segmentation separates the conflicting requirements of high conductivity and low defect formation into distinct spatial zones.
2Reliability
If high Mg doping concentration is used in AlGaN layers, then p-type conductivity improves, but hole mobility decreases due to increased scattering
Solution Approach 1:
Different regions are assigned different doping qualities: the contact layer uses heavy doping (1e19-1e21 atoms/cm³) to maximize conductivity, while the electron blocking layer uses light or zero doping to maximize hole mobility. Each region's doping level is optimized for its specific function.
3Illumination intensity
If increased aluminum molar fraction is used in AlGaN, then bandgap increases for UV emission, but acceptor activation energy increases making p-type doping more difficult
Solution Approach 1:
The device structure is segmented into an active region with high Al content (0.6-0.8) for UV emission and a contact layer with lower Al content (0.1-0.3) that is easier to dope. This segmentation allows the high-Al region to optimize optical performance while the low-Al region optimizes electrical performance.
Solution Approach 2:
The electron blocking layer acts as an intermediary between the high-Al active region and the low-Al contact layer, providing a transition zone that manages both optical and electrical requirements while preventing electron leakage into the contact layer.
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.