HEMT Substrate Lattice Transition Layer Stress Management
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Solution Overview
Problem
High-electron-mobility field effect transistors (HEMTs) face challenges with high leakage current and reduced voltage blocking capability due to lattice mismatch between silicon and GaN materials, leading to strain and defects, and the need for thicker buffer layers increases production costs.
Innovation Solution
A compound semiconductor device structure with a silicon substrate featuring a highly doped layer to suppress electron inversion, a nucleation region with a doped type III-V semiconductor nitride layer, and a lattice transition layer to alleviate stress, along with a second substrate layer to mitigate electron emission and tunneling mechanisms, enhancing vertical breakdown strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a thick buffer layer (5 μm or more) is used to improve voltage blocking capability, then voltage rating increases to 400 V, but production cost increases due to difficult epitaxial process control
Solution Approach 1:
The buffer layer is segmented into multiple sub-layers with different thicknesses and doping concentrations. The first buffer layer has lower doping concentration and the second buffer layer has higher doping concentration, allowing each layer to be optimized independently for both voltage blocking and manufacturability
Solution Approach 2:
The invention changes the doping concentration parameter across different buffer layer regions. By creating a gradient or stepped doping profile (lower in first buffer layer, higher in second buffer layer), the device achieves high voltage blocking capability while maintaining better epitaxial process control and reducing production costs
2Ease of manufacture
If direct epitaxial growth of GaN on silicon is attempted, then availability and cost of substrate improve, but lattice mismatch causes strain and defects in GaN material
Solution Approach 1:
A nucleation layer is introduced as an intermediary between the silicon substrate and the GaN buffer layer. This nucleation layer serves as a transition interface that reduces the direct lattice mismatch between silicon and GaN, thereby reducing strain and defect formation while maintaining the benefits of using silicon substrates
Solution Approach 2:
The invention uses a composite structure consisting of silicon substrate, nucleation layer, and GaN buffer layer with specific doping profiles. This composite material approach allows each layer to contribute its advantageous properties: silicon provides cost-effectiveness and availability, while the engineered GaN structure provides high voltage blocking capability with reduced defects
3Power
If HEMT structure is used for power transistor applications, then switching capability for high power applications improves, but leakage current increases due to band-to-band tunneling mechanisms
Solution Approach 1:
The invention changes the doping concentration parameter in the buffer layer to optimize the balance between power switching capability and leakage current. By carefully controlling the doping profile, the device achieves high voltage blocking capability for power applications while suppressing band-to-band tunneling mechanisms that cause leakage
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 significantly reduces leakage current and increases voltage blocking capability, achieving several orders of magnitude lower breakdown current and higher voltage ratings with improved device reliability and cost-effectiveness.
Implementation Method 1
The lattice transition layer is configured to alleviate stress arising in the silicon substrate due to lattice mismatch between the silicon substrate and other layers in the compound semiconductor device structure
Implementation Method 2
The second substrate layer is configured to suppress an inversion layer in the silicon substrate arising at an interface between the silicon substrate and the nucleation region
Implementation Method 3
the need for thicker buffer layers increases production costs... A compound semiconductor device structure with a silicon substrate featuring a highly doped layer to suppress electron inversion... The second substrate layer is configured to suppress an inversion layer... and mitigate electron emission and tunneling mechanisms
Data Source
AI summary
A compound semiconductor device structure having a main surface and a rear surface includes a silicon substrate including first and second substrate layers. The first substrate layer extends to the rear surface. The second substrate layer extends to a first side of the substrate that is opposite from the rear surface such that the first substrate layer is completely separated from the first side by the second substrate layer. A nucleation region is formed on the first side of the silicon substrate and includes a nitride layer. A lattice transition layer is formed on the nucleation region and includes a type III-V semiconductor nitride. The lattice transition layer is configured to alleviate stress arising in the silicon substrate due to lattice mismatch between the silicon substrate and other layers in the compound semiconductor device structure. The second substrate layer is configured to suppress an inversion layer in the silicon substrate.