p-Type AlGaN Layer Grading for VCSEL Carrier Injection and Life
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Solution Overview
Problem
Vertical cavity light-emitting elements face a trade-off between high carrier injection efficiency and element life due to excessive p-type dopant concentration in the p-type AlGaN layer, leading to dopant diffusion and defect spread in the active layer.
Innovation Solution
A vertical cavity light-emitting element with a p-type AlGaN layer structured into three regions of varying Al compositions and Mg concentrations, controlled through precise growth steps using MOCVD, ensuring optimal carrier injection while minimizing dopant diffusion and defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the concentration of p-type dopant in the p-type AlGaN layer is increased to improve carrier injection efficiency, then the carrier injection efficiency is improved, but the element life is likely to decrease due to diffusion of the p-type dopant into the active layer and spread of defects
Solution Approach 1:
The p-type AlGaN layer is divided into three distinct regions (first, second, and third regions) with different Al compositions and dopant concentrations. The first region has lower Al composition and lower dopant concentration to prevent diffusion into the active layer, while the second and third regions have higher Al composition and higher dopant concentration to ensure high carrier injection efficiency. This segmentation allows each region to fulfill different functional requirements simultaneously.
Solution Approach 2:
Different regions within the p-type AlGaN layer are assigned different local properties: the first region (adjacent to the active layer) has lower Al composition (20-30%) and lower dopant concentration to minimize diffusion and defect spread, while the second region (intermediate layer) has higher Al composition (30-50%) and higher dopant concentration to provide strong electron blocking and carrier injection. This local quality variation optimizes both reliability and productivity at different positions within the layer.
2Reliability
If the Al composition of the electron blocking layer is increased to improve band gap energy and suppress electron carrier overflow, then the electron blocking capability is improved, but the dopant diffusion into the active layer is exacerbated
Solution Approach 1:
The electron blocking function is segmented between different regions: the second region (intermediate layer) with high Al composition (30-50%) provides the primary electron blocking capability through its wide band gap, while the first region with lower Al composition (20-30%) acts as a diffusion barrier to prevent dopant migration into the active layer. This segmentation allows the system to achieve strong electron blocking without excessive dopant diffusion.
Solution Approach 2:
The Al composition is varied locally within the p-type AlGaN layer to optimize different functions at different positions. The intermediate region (second region) has higher Al composition to provide strong electron blocking capability where it is most needed, while the region adjacent to the active layer (first region) has lower Al composition to minimize the harmful effect of dopant diffusion. This local quality optimization resolves the contradiction between electron blocking capability and dopant diffusion prevention.
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 maintains high carrier injection efficiency while extending the element's life by suppressing dopant diffusion and defect formation, resulting in a long-life, highly efficient vertical cavity light-emitting element.
Implementation Method 1
suppressing a decrease in an element life due to diffusion of the p-type dopant into the active layer
Implementation Method 2
a manufacturing method of the vertical cavity light-emitting element by a metal-organic chemical vapor deposition (MOCVD)
Data Source
AI summary
A vertical cavity light-emitting element includes a p-type AlGaN layer that contains Mg and includes three or more stacked AlGaN layers with different Al compositions. When the AlGaN layer is divided into, from an active layer side, a first region having a layer thickness of 1/10, a second region having a layer thickness of ⅖, and a third region having a layer thickness of ½ in this order, a size relationship among Al compositions indicated by an Al composition curve is the first region<the third region<the second region. The Mg concentration indicated by an Mg concentration curve is less than 3x1019 atoms/cm3 throughout an entire thickness of the AlGaN layer. A size relationship among Mg concentrations is the first region<the second region<the third region. The Mg concentration in at least part of the second region is 3×1018 atoms/cm3 or more.