Co-doped p-type 4H-SiC Crystal Growth via Nitrided Aluminum Sublimation
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Solution Overview
Problem
Current methods fail to achieve sufficiently low resistivity in p-type 4H—SiC single crystals due to lower hole mobility, higher ionization energy of aluminum or boron, and increased polymorphs leading to crystallinity deterioration.
Innovation Solution
A sublimation method is used to introduce nitrogen at high concentrations into p-type 4H—SiC single crystals with nitrided aluminum, co-doping with aluminum to prevent polymorphs and achieve low resistivity, with specific concentration ranges for aluminum and nitrogen, and a nitrogen gas atmosphere during growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If aluminum or boron is used as acceptor doping to create p-type 4H-SiC, then the material achieves p-type conductivity, but the ionization energy is high and activation rate is low resulting in insufficiently low resistivity
Solution Approach 1:
The patent changes the doping parameters by introducing nitrogen alongside aluminum, creating a co-doped system where nitrogen's lower ionization energy (2.4 eV) compensates for aluminum's high ionization energy (0.06 eV), achieving lower overall resistivity while maintaining p-type conductivity
Solution Approach 2:
The patent creates a composite doping structure by combining aluminum (acceptor) and nitrogen (donor) in specific concentrations, forming a co-doped p-type 4H-SiC material that leverages the complementary properties of both dopants to achieve low resistivity
2Reliability
If the doping amount of aluminum is increased to lower resistivity, then more p-type carriers are introduced, but polymorphs increase resulting in deterioration of crystallinity
Solution Approach 1:
The patent optimizes the doping concentration parameters by maintaining aluminum at 1.0×10^20/cm³ or more while introducing nitrogen at 2.0×10^19/cm³ or more, a specific parameter combination that prevents polymorph formation while achieving low resistivity
Solution Approach 2:
Nitrogen acts as an intermediary element that mediates between aluminum doping and crystal structure stability, preventing the formation of polymorphs (3C-SiC, 6H-SiC) that would otherwise occur at high aluminum concentrations, thus maintaining 4H-SiC crystallinity
3Reliability
If conventional doping methods are used to achieve low resistivity, then doping concentration can be increased, but the process becomes complex and difficult to control
Solution Approach 1:
The patent performs preliminary action by pre-nitriding the aluminum raw material before crystal growth, so that nitrogen is already incorporated into the aluminum source, simplifying the subsequent doping process and ensuring consistent co-doping without requiring separate nitrogen introduction steps
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 p-type 4H—SiC single crystal with a resistivity of 100 mΩcm or less, high crystallinity, and reduced stacking faults, suitable for high-breakdown voltage devices like n-channel IGBTs.
Implementation Method 1
a sublimation step of sublimating a nitrided aluminum raw material and a SiC raw material
Implementation Method 2
using a nitrided aluminum raw material
Data Source
AI summary
A method for producing a p-type 4H—SiC single crystal includes sublimating a nitrided aluminum raw material and a SiC raw material. Further, there is a stacking of a SiC single crystal, which is co-doped with aluminum and nitrogen, on one surface of a seed crystal.