Nitride Semiconductor UV Light-Emitting Element Parasitic Resistance Reduction
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Solution Overview
Problem
The wall plug efficiency of nitride semiconductor ultraviolet light-emitting elements is limited due to high parasitic resistance in the n-type AlGaN-based semiconductor layer, which reduces voltage efficiency and overall light emission efficiency, especially as the emission wavelength shortens.
Innovation Solution
Incorporating a plurality of thin film-like Ga-rich layers with a high Ga composition ratio in the n-type layer, spaced apart vertically and inclined, to reduce parasitic resistance and enhance carrier density injection into the active layer, thereby improving internal quantum efficiency and voltage efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a p-type contact layer with low AlN molar fraction is formed to improve ohmic contact with the p-electrode, then contact quality is improved, but ultraviolet light emitted toward the p-type nitride semiconductor layer side is absorbed in the p-type contact layer and cannot be effectively extracted
Solution Approach 1:
The patent segments the contact layer into multiple functional layers: a p-type contact layer with low AlN molar fraction for ohmic contact, and a p-type cladding layer with higher AlN molar fraction for light extraction. This segmentation allows each layer to optimize its specific function without compromising the other.
Solution Approach 2:
Different regions of the contact structure have different AlN molar fractions tailored to their specific functions. The contact layer has low AlN content for electrical contact, while the cladding layer has high AlN content for optical performance, creating local quality variations that resolve the contradiction.
2Loss of energy
If the AlN molar fraction of the p-type nitride semiconductor layer is increased to improve light extraction, then light extraction efficiency is improved, but it becomes difficult to form a good ohmic contact with the p-electrode
Solution Approach 1:
The contact structure is segmented into multiple layers with different AlN molar fractions. The lower contact layer maintains low AlN content for electrical contact, while upper cladding layers have high AlN content for light extraction, allowing both requirements to be satisfied simultaneously.
Solution Approach 2:
The solution moves from a single-layer structure to a multi-layer vertical structure, adding the dimension of layer stacking. This allows the system to satisfy conflicting requirements at different vertical positions within the same contact structure.
3Illumination intensity
If the AlN molar fraction is increased to achieve shorter emission wavelength, then ultraviolet light emission capability is improved, but parasitic resistance in the n-type AlGaN-based semiconductor layer increases and reduces voltage efficiency
Solution Approach 1:
The n-type layer structure uses local quality variation by incorporating Ga-rich layers with different compositions at specific positions. The base n-type AlGaN layer has high AlN content for UV emission, while embedded Ga-rich regions provide low-resistance conduction paths, allowing both UV capability and low parasitic resistance.
Solution Approach 2:
The n-type contact structure uses a composite of n-type AlGaN semiconductor material and Ga-rich layers. This composite structure combines the high AlN molar fraction material for UV emission with Ga-rich regions for electrical conduction, resolving the contradiction between emission wavelength and parasitic resistance.
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 improved carrier injection and reduced parasitic resistance lead to increased internal quantum efficiency and voltage efficiency, enhancing the overall wall plug efficiency of the ultraviolet light-emitting element.
Implementation Method 1
In the n-type layer below at least the first region of the upper surface of the n-type layer, a plurality of thin film-like Ga-rich layers that is a part of the n-type layer having a locally high Ga composition ratio exists spaced apart from each other in a vertical direction
Implementation Method 2
by passing a forward current from the p-type nitride semiconductor layer toward the n-type nitride semiconductor layer, light emission corresponding to the band gap energy due to recombination of carriers (electrons and holes) occurs in the active layer
Data Source
AI summary
To improve a wall plug efficiency in a nitride semiconductor light-emitting element for extracting ultraviolet light emitted from an active layer toward an n-type nitride semiconductor layer side to outside of the element. In the n-type AlGaN-based semiconductor layer 21 constituting the nitride semiconductor light-emitting element 1, a plurality of thin film-like Ga-rich layers that is a part of the n-type layer 21 having a locally high Ga composition ratio exists spaced apart from each other in a vertical direction that is orthogonal to the upper surface of the n-type layer 21, an extending direction of at least a part of the plurality of Ga-rich layers on a first plane parallel to the vertical direction is inclined with respect to an intersection line between the upper surface of the n-type layer and the first plane, the plurality of Ga-rich layers exists in stripes on the second plane parallel to the upper surface of the n-type layer 21 in an upper layer region having a thickness of 100 nm or less at lower side from the upper surface of the n-type layer 21, AlN molar fractions of the Ga-rich layers 21b are greater than AlN molar fraction of a well layer 22b in an active layer 22 constituting the light-emitting element 1.