AlGaN Buffer Structure for Stress Control in DUV LEDs
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Solution Overview
Problem
The growth of high-quality aluminum nitride (AlN) buffer layers on substrates like sapphire, silicon carbide, and silicon is challenging due to high dislocation density and stress issues, which affects the efficiency and reliability of deep ultraviolet light emitting diodes (DUV LEDs).
Innovation Solution
A semiconductor structure with a buffer layer grown using a multi-stage process, where nucleation islands are formed with controlled V/III ratio and growth temperature to achieve a compressive stress range of 0.1 GPa to 2.0 GPa, reducing dislocation density and stress in subsequent semiconductor layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a thick AlGaN epitaxial layer is grown to reduce current crowding, then device efficiency is improved, but tensile strain and dislocation density increase causing cracks and reduced reliability
Solution Approach 1:
The buffer layer is segmented into multiple functional layers including a first buffer layer with higher aluminum content and a second buffer layer with lower aluminum content. This segmentation allows each layer to handle different stress conditions, with the first layer providing compressive stress to counterbalance the tensile strain in the thick AlGaN device layer, while the second layer provides a transition to reduce dislocation density.
Solution Approach 2:
The invention changes the compositional parameter of the buffer layers by using varying aluminum content (AlxGa1-xN with different x values). The first buffer layer uses higher aluminum content (0.3≤x≤1) to generate compressive stress, while the second buffer layer uses lower aluminum content (0≤x<0.3) to provide a graded transition, thereby controlling stress distribution and reducing dislocation propagation throughout the structure.
2Stress or pressure
If a superlattice structure is grown to reduce biaxial tensile strain, then stress control is improved, but compositional uniformity and manufacturing complexity deteriorate
Solution Approach 1:
Instead of using a complex AlN/AlGaN superlattice structure to manage stress, the invention inverts the approach by using a simplified AlGaN/AlGaN heterostructure with varying aluminum content. The higher-aluminum first buffer layer generates compressive stress to counterbalance the tensile strain, eliminating the need for complex superlattice patterns while achieving effective stress control.
Solution Approach 2:
The invention applies local quality by assigning different aluminum content to different regions of the buffer structure. The first buffer layer region has higher aluminum content specifically to generate compressive stress where needed, while the second buffer layer has lower aluminum content to provide a graded transition zone, optimizing stress management without requiring complex superlattice structures throughout the entire buffer region.
3Reliability
If patterned substrate approaches are used to reduce dislocation density, then dislocation control is improved, but manufacturing cost and process complexity increase
Solution Approach 1:
The invention performs preliminary action by growing the first buffer layer with higher aluminum content directly on the substrate before growing the device layers. This first buffer layer is prepared in advance to establish the desired compressive stress state and filter dislocations from the substrate, creating an optimized foundation that simplifies subsequent manufacturing steps compared to post-growth patterning approaches.
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 results in a semiconductor structure with reduced dislocation density and stress, enhancing the reliability and efficiency of DUV LEDs by controlling stress and dislocation propagation, leading to improved device performance and extended operating lifetime.
Implementation Method 1
The buffer structure can have an effective lattice constant and a thickness such that an overall stress in the set of semiconductor layers at room temperature is compressive and is in a range between approximately 0.1 gigapascal (GPa) and 2.0 GPa
Data Source
AI summary
A semiconductor structure comprising a buffer structure and a set of semiconductor layers formed adjacent to a first side of the buffer structure is provided. The buffer structure can have an effective lattice constant and a thickness such that an overall stress in the set of semiconductor layers at room temperature is compressive and is in a range between approximately 0.1 GPa and 2.0 GPa. The buffer structure can be grown using a set of growth parameters selected to achieve the target effective lattice constant a, control stresses present during growth of the buffer structure, and/or control stresses present after the semiconductor structure has cooled.