Nitride Semiconductor UV Light-Emitting Element With Segmented Contact Layers
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Solution Overview
Problem
Conventional techniques for improving external quantum efficiency of nitride semiconductor ultraviolet light-emitting elements with emission wavelengths of 355 nm or smaller are ineffective due to absorption of light by the p-type nitride semiconductor layer, preventing effective reflection and utilization of emitted light.
Innovation Solution
A nitride semiconductor ultraviolet light-emitting element with a p-type contact layer that has openings penetrating through to the p-type cladding layer, allowing ultraviolet light to reach a reflective metal layer without absorption, and an n-type contact layer with a lower AlN molar fraction to reduce parasitic resistance and enhance light extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a p-type contact layer is formed on the p-type cladding layer to reduce contact resistance, then electrical conductivity is improved, but ultraviolet light is absorbed by the p-type contact layer, reducing light extraction efficiency
Solution Approach 1:
The p-type contact layer is segmented by forming openings (apertures) that penetrate through it, allowing ultraviolet light to pass through to the reflective layer below while maintaining electrical contact in the surrounding regions. This segmentation resolves the contradiction by separating the electrical conduction function from the light transmission function within the same layer structure.
Solution Approach 2:
Different regions of the p-type contact layer have different properties: the openings provide light transmission pathways, while the surrounding contact layer material provides electrical conductivity. This local differentiation allows the layer to simultaneously satisfy both electrical and optical requirements.
2Illumination intensity
If the AlN molar fraction of the p-type cladding layer is increased to achieve shorter emission wavelength, then emission wavelength is reduced, but contact resistance with the p-type contact layer increases
Solution Approach 1:
The p-type contact layer is segmented with openings to reduce light absorption, and the n-type contact layer is similarly segmented, allowing both layers to maintain their respective functions of electrical contact and light transmission despite the high AlN molar fraction in the cladding layer.
Solution Approach 2:
The contact layers are designed with local quality variations where the openings provide light transmission pathways while the surrounding material provides electrical conductivity, enabling the system to handle the increased contact resistance through structural optimization.
3Reliability
If conventional reflective structures are used with a continuous p-type contact layer, then electrical contact is maintained, but light absorption by the continuous layer prevents effective reflection
Solution Approach 1:
Both the p-type and n-type contact layers are segmented by forming openings that penetrate through them, creating a patterned structure that allows ultraviolet light to reach the reflective layer while maintaining electrical contact in the surrounding regions.
Solution Approach 2:
The solution moves from a two-dimensional continuous contact layer to a three-dimensional patterned structure with vertical openings, allowing light to pass through the layer in the vertical dimension while maintaining horizontal electrical contact.
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 solution effectively improves external quantum efficiency by ensuring that ultraviolet light is reflected and utilized, while reducing parasitic resistance and power consumption, thereby enhancing light emission and device performance.
Implementation Method 1
a reflective layer for reflecting the ultraviolet light emitted from the active layer is formed at least on the opening portion
Implementation Method 2
a p-type contact layer configured of a p-type AlGaN semiconductor layer that absorbs ultraviolet light emitted from the active layer
Data Source
AI summary
A nitride semiconductor ultraviolet light-emitting element is formed by laminating at least an n-type cladding layer configured of an n-type AlGaN semiconductor layer, an active layer including an AlGaN semiconductor layer having band gap energy of 3.4 eV or larger, and a p-type cladding layer configured of a p-type AlGaN semiconductor layer. A p-type contact layer configured of a p-type AlGaN semiconductor layer that absorbs ultraviolet light emitted from the active layer is formed on the p-type cladding layer. The p-type contact layer has an opening portion penetrating through to a surface of the p-type cladding layer. A p-electrode metal layer that makes Ohmic contact or non-rectifying contact with the p-type contact layer is formed on the p-type contact layer so as not to completely block the opening portion. A reflective metal layer for reflecting the ultraviolet light is formed at least on the opening portion and covers the surface of the p-type cladding layer that is exposed through the opening portion either directly or through a transparent insulating layer that allows the ultraviolet light to pass therethrough.