HEMT Buffer Superlattice Structure for Lattice Defect Control
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Solution Overview
Problem
High electron mobility transistors (HEMTs) face issues with lattice defects and thermal expansion coefficient mismatch, leading to reliability and performance problems due to the mismatch between semiconductor materials, which existing solutions like protruding epitaxial structures or insulating masks do not adequately address.
Innovation Solution
A semiconductor device is designed with a buffer layer comprising a first superlattice layer with heteromaterials alternately arranged horizontally and a second superlattice layer with heteromaterials vertically stacked, which deviates lattice defects laterally, preventing their upward transmission and improving lattice and thermal expansion coefficient compatibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If gallium nitride based materials are used to form HEMTs, then high power and high frequency performance is achieved, but lattice defects and thermal expansion coefficient mismatch occur
Solution Approach 1:
The buffer layer is segmented into multiple sub-layers with different compositions (AlN, GaN, AlGaN) arranged in superlattice structures. This segmentation allows gradual transition of lattice constants and thermal expansion coefficients, effectively reducing mismatch defects while maintaining the high power performance of GaN-based HEMTs
Solution Approach 2:
The patent employs composite buffer layer structures combining different III-nitride materials (AlN, GaN, AlGaN) with varying aluminum compositions. These composite structures leverage the advantageous properties of each material to mitigate lattice mismatch and thermal expansion issues while enabling high power device operation
2Reliability
If protruding epitaxial structures or insulating masks are used to address lattice defects, then defect propagation is partially reduced, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The buffer layer composition is locally optimized at different depths and positions, with aluminum content varying through the layer structure. This local quality variation allows targeted defect mitigation at critical interfaces while maintaining simplicity in overall device architecture, avoiding the need for complex protruding structures or masks
3Reliability
If buffer layer thickness is increased to reduce lattice mismatch, then defect density decreases, but manufacturing time and cost increase
Solution Approach 1:
The buffer layer employs periodic superlattice structures with repeating units of different materials and thicknesses. This periodic composition allows achieving excellent lattice matching within a relatively thin total buffer thickness, significantly reducing fabrication time compared to using uniformly thick buffer layers while maintaining low defect density
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 configuration significantly enhances the reliability and performance of HEMTs by effectively eliminating lattice defects and ensuring better structural integrity and electrical properties.
Implementation Method 1
a first superlattice layer having at least two heteromaterials alternately arranged in a horizontal direction, and a second superlattice layer having at least two heteromaterials vertically stacked along a vertical direction... to prevent lattice defects from extending or diffusing upwardly
Implementation Method 2
A two-dimensional electron gas (2DEG) may be generated by the piezoelectricity property of the GaN-based materials, and the switching velocity may be enhanced because of the higher electron velocity and the higher electron density of the two-dimensional electron gas
Data Source
AI summary
The present disclosure provides a semiconductor device, the semiconductor device including a substrate, a nucleation layer, a buffer layer, an active layer and a gate electrode. The nucleation layer is disposed on the substrate, and the buffer layer is disposed on the nucleation layer, wherein the buffer layer includes a first superlattice layer having at least two heteromaterials alternately arranged in a horizontal direction, and a second superlattice layer having at least two heteromaterials vertically stacked along a vertical direction. The at least two heteromaterials stack at least once within the second superlattice layer. The active layer is disposed on the buffer layer, and the gate electrode is disposed on the active layer.