AlGaN Grading Layers for Semiconductor Power Device Lattice Mismatch
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Solution Overview
Problem
Group III-V semiconductor power devices face issues with breakdown voltage and leakage current due to lattice mismatch between substrates and epitaxial materials, affecting switch speed and efficiency.
Innovation Solution
A semiconductor power device structure is implemented with a substrate, a first semiconductor layer, a grading layer with varying lattice constants, and an interlayer of different composition, which reduces defect propagation and enhances epitaxial quality by forming a two-dimensional electron gas through piezoelectric effects, improving electron mobility and concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If group III-V semiconductor materials are used to improve switch speed and efficiency, then electron mobility and concentration are improved, but breakdown voltage and leakage current issues worsen due to lattice mismatch
Solution Approach 1:
The epitaxial structure is segmented into multiple layers with gradually changing composition (AlGaN layers with increasing Al content from bottom to top). This segmentation approach divides the lattice mismatch problem into manageable steps, where each layer transitions gradually to the next, reducing dislocation density while maintaining the high electron mobility characteristics of group III-V materials
Solution Approach 2:
AlGaN grading layers serve as intermediary layers between the substrate and the GaN-based active layers. These intermediate layers with compositionally graded Al content act as a transition zone that mediates the lattice mismatch between the substrate and the high-electron-mobility GaN layers, reducing defect propagation while preserving the piezoelectric effect needed for 2DEG formation
2Quantity of substance
If group III-V semiconductor materials are used to improve electron concentration, then electrical current output is improved, but leakage current increases due to epitaxial quality issues
Solution Approach 1:
The structure is divided into multiple AlGaN grading layers with progressively increasing Al content, creating discrete steps in lattice constant transition. This segmentation reduces the cumulative dislocation density that would otherwise propagate through the structure, thereby reducing leakage current paths while maintaining high electron concentration in the 2DEG channels
Solution Approach 2:
The composition parameter (Al content) is systematically changed across the grading layers, transitioning from lower Al content near the substrate to higher Al content near the GaN active layers. This parameter change strategy optimizes the balance between lattice matching (reducing defects and leakage) and maintaining the piezoelectric field strength needed for high electron concentration
3Ease of manufacture
If epitaxial growth is performed to form semiconductor layers, then device functionality is achieved, but dislocation concentration increases due to lattice mismatch
Solution Approach 1:
The epitaxial growth process is segmented into multiple stages, with each stage forming a specific AlGaN layer with a defined composition range. This segmented approach allows controlled progression through the lattice mismatch transition, reducing dislocation generation at each interface while maintaining overall manufacturing feasibility through standard MOCVD or MBE processes
Solution Approach 2:
The AlGaN grading layers are formed preliminarily before the final GaN active layers. This preliminary action creates a defect-filtering structure that prevents dislocation propagation to subsequent layers, ensuring high epitaxial quality in the device-active regions while using compositionally graded buffer layers that are later covered by the functional GaN structures
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 proposed structure effectively decreases defect density, enhances epitaxial layer quality, and improves breakdown voltage and leakage current issues, enabling high-frequency, high-voltage operation with increased power efficiency.
Implementation Method 1
forming a two-dimensional electron gas through piezoelectric effects
Data Source
AI summary
A semiconductor power device, comprising: a substrate; a first semiconductor layer with a first lattice constant formed on the substrate; a first grading layer formed on the first semiconductor layer and comprising a first portion; a second grading layer formed on the first grading layer; a second semiconductor layer with a second lattice constant formed on the second grading layer; a first interlayer formed in the first grading layer and adjacent to the first portion of the first grading layer; and a second interlayer formed in the second grading layer; wherein the first interlayer comprises a first superlattice including a series of Alx1Ga1-x1N/Aly1Ga1-y1N alternate layers, (x1-y1)≧0.2, and the second interlayer comprises a second superlattice including a series of Alx2Ga1-x2N/Aly2Ga1-y2N alternate layers, (x2-y2)≧0.2, wherein the average of x1 and y1 is larger than that of x2 and y2.