Nitride Semiconductor UV Light-Emitting Element
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Solution Overview
Problem
Conventional nitride semiconductor light-emitting elements with a center emission wavelength of 355 nm or smaller face challenges in enhancing external quantum efficiency due to light absorption by p-type nitride semiconductor layers and ineffective reflection of light at the n-electrode, leading to reduced light extraction efficiency.
Innovation Solution
A nitride semiconductor ultraviolet light-emitting element design featuring an n-type cladding layer, an active layer with a band gap energy of 3.4 eV or higher, a p-type cladding layer, and a reflective metal layer that re-reflects light towards the light exit surface, integrated with an n-electrode and a reflective metal layer to enhance light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a p-type contact layer is used to improve electrical contact, then electrical conductivity is improved, but light absorption increases reducing light extraction efficiency
Solution Approach 1:
The contact structure is segmented into a p-type contact layer for electrical connection and a separate reflective layer for light management. The reflective layer is positioned to intercept light before it reaches the p-type contact layer, allowing the contact layer to focus on electrical function while the reflective layer handles light extraction.
Solution Approach 2:
A reflective layer is introduced as an intermediary between the light-emitting region and the p-type contact layer. This reflective layer serves as a mediator that redirects light away from the light-absorbing p-type contact layer, preventing energy loss while maintaining electrical contact functionality.
2Loss of energy
If light is reflected at the n-electrode interface, then light extraction is improved, but reflection efficiency is insufficient leading to energy loss
Solution Approach 1:
The reflective properties at the n-electrode interface are enhanced by changing the parameters of the reflective layer, such as its material composition, thickness, and optical constants. These parameter changes increase the reflectivity at the desired wavelength, improving light extraction efficiency while minimizing energy loss.
3Loss of energy
If the AlN molar fraction in cladding layers is increased to reduce light absorption, then light extraction is improved, but electrical contact properties deteriorate
Solution Approach 1:
Different regions of the device are assigned different AlN molar fractions optimized for their specific functions. The cladding layers have higher AlN content to reduce light absorption and improve light extraction, while the contact layer maintains lower AlN content to ensure good electrical contact properties. This local optimization resolves the contradiction between optical and electrical performance.
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 design significantly improves external quantum efficiency by effectively re-reflecting light that would otherwise be absorbed, increasing the amount of emitted light extracted from the nitride semiconductor ultraviolet light-emitting element.
Implementation Method 1
a first reflective metal layer which reflects ultraviolet light emitted from the active layer
Implementation Method 2
an n-type cladding layer configured of an n-type AlGaN semiconductor layer... a p-type cladding layer configured of a p-type AlGaN semiconductor layer... where an AlN molar fraction of the n-type cladding layer is larger than an AlN molar fraction of the active layer
Data Source
AI summary
An active layer including an AlGaN semiconductor layer having a band gap energy of 3.4 eV or higher and a p-type cladding layer configured of a p-type AlGaN semiconductor layer and located above the active layer are formed in a first region on the n-type cladding layer, the first region being in a plane parallel to a surface of the n-cladding layer configured of an n-type AlGaN semiconductor layer. An n-electrode metal layer making Ohmic contact with the n-type cladding layer is formed on an adjacent region to the first region in a second region which is a region other than the first region on the n-type cladding layer. A first reflective metal layer reflecting ultraviolet light emitted from the active layer is formed on a surface of the n-type cladding layer in the second region other than the adjacent region. The n-electrode metal layer is arranged between the first region and a region in which the first reflective metal layer contacts the surface of the n-type cladding layer.