Semiconductor Layered Structure for Quantum Dot Formation
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Solution Overview
Problem
The formation of quantum dot structures in light emitting devices using group III nitrides is limited by the difference in lattice constant between the matrix region and the island crystals, leading to conductivity issues and constraints on composition, as well as challenges in maintaining compression stress for effective quantum dot formation.
Innovation Solution
A method of epitaxial growth using MBE to form a semiconductor layer with a matrix region that maintains compression stress, allowing for the formation of quantum dots with a third group III nitride doped with rare-earth or transition-metal elements, and a lattice constant alignment that compensates for the difference between the quantum dots and the matrix region, enabling reduced compositional constraints and improved carrier confinement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the composition of the matrix region is optimized for quantum dot formation (higher Al content), then quantum dot structure formation is improved, but conductivity decreases
Solution Approach 1:
The device is divided into functionally distinct regions: a matrix region with higher Al content optimized for quantum dot formation and emission, and a cladding region with lower Al content optimized for carrier confinement and conductivity. This segmentation allows each region to be independently optimized for its specific function without compromise.
Solution Approach 2:
Different Al compositions are assigned to different spatial locations within the device structure. The matrix region has higher Al content (0.3-0.7) for optimal quantum dot formation, while the cladding region has lower Al content (0.0-0.2) for optimal conductivity and carrier confinement, creating local quality variations that satisfy conflicting requirements.
2Stress or pressure
If the thickness of the AlGaN layer is increased to maintain compression stress, then stress maintenance is improved, but crack generation increases
Solution Approach 1:
The Al composition parameter is varied between the matrix region (higher Al) and cladding region (lower Al) to control the magnitude and distribution of compression stress. By adjusting these compositional parameters, the stress profile is optimized to maintain effective compression for quantum dot formation while staying below the critical thickness for crack generation.
Solution Approach 2:
The device employs a composite structure with multiple AlGaN layers of different compositions. The matrix region and cladding region form a composite system where the higher Al content in the matrix provides compression stress while the lower Al content in the cladding reduces overall stress accumulation, preventing cracks while maintaining stress where needed.
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
This approach enhances the emission efficiency of light emitting devices by maintaining desirable stress conditions, allowing for effective carrier confinement and the emission of desired hues, including white light, while reducing compositional limitations in the matrix region.
Implementation Method 1
The formation of quantum dot structures by self-organization as disclosed in Japanese Patent Application Laid-open No. 2002-368267
Implementation Method 2
an AlGaN layer is epitaxially formed on the AlN template substrate by using a MOCVD technique
Implementation Method 3
Each layer forming the matrix region is formed while maintaining compression stress in a direction generally perpendicular to a direction of deposition
Implementation Method 4
dispersing, in a matrix region, island crystals which are so minute as to cause quantum effects and which are doped with a predetermined rare-earth or transition-metal element, and then by using the resultant carrier confinement effect of quantum dots
Implementation Method 5
a lattice constant alignment that compensates for the difference between the quantum dots and the matrix region
Data Source
AI summary
In formation of a quantum dot structure in a light emitting layer, a matrix region (an n-type conductive layer and matrix layers) is formed on a growth underlying layer of AlN whose abundance ratio of Al is higher (or whose lattice constant is smaller) than that in the matrix region by an MBE technique, thereby to realize conditions where compression stress is caused in an in-plane direction perpendicular to the direction of growth of the matrix region, and then to form island crystals by self-organization in the presence of this compression stress. The compression stress inhibits an increase in lattice constant caused by the reduced abundance ratio of Al in the matrix region, i.e., to compensate for a difference in lattice constant between the island crystals and the matrix region. The compression stress functions to enlarge compositional limits for formation of the island crystals by self-organization to the Ga-rich side.