Silicon Carbide Single Crystal Doping for Stable High Resistivity
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Solution Overview
Problem
Silicon carbide single crystals used as substrates for high-power transistors face issues with parasitic capacitance and decreased output power at high temperatures due to unintentional nitrogen impurities and temperature-dependent resistivity changes, as well as temporary carrier trapping by vanadium doping, leading to unstable transistor properties.
Innovation Solution
A silicon carbide single crystal with a positive correlation between temperature and resistivity from room temperature to 400°C, achieving an electric resistivity of at least 1×10^7 Ω·cm, utilizing a balance of donor and acceptor dopants to ensure hole conduction and maintain high resistivity across temperature ranges, with a concentration of transition elements kept low to prevent deep trap formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the purity of silicon carbide single crystal is increased to raise electric resistivity, then electric resistivity increases, but nitrogen impurities still remain and act as donors causing resistivity to decrease with temperature increase
Solution Approach 1:
The patent introduces aluminum as an intermediary dopant that compensates for nitrogen donors. Aluminum atoms replace silicon atoms in the crystal lattice and provide holes that counterbalance the electron donation from nitrogen impurities, thereby maintaining high resistivity even when nitrogen is present. This mediator approach allows the system to tolerate nitrogen impurities while achieving the desired electrical properties.
Solution Approach 2:
The patent changes the chemical composition parameter by deliberately adding aluminum dopant at controlled concentrations (1×10^16 to 1×10^18 atoms/cm³). This parameter change transforms the electrical characteristics of the silicon carbide crystal, creating a p-type or compensated material that maintains stable high resistivity across temperature ranges despite the presence of nitrogen impurities.
2Reliability
If vanadium doping is used to capture electrons and increase electric resistivity, then electric resistivity increases at room temperature, but carriers are temporarily captured causing unstable transistor properties
Solution Approach 1:
The patent extracts or removes vanadium dopant from the system, replacing it with aluminum dopant. This elimination of the harmful element (vanadium that causes temporary carrier trapping) while retaining the beneficial function (achieving high resistivity through aluminum compensation of nitrogen donors) resolves the contradiction between resistivity enhancement and device stability.
3Reliability
If highly purified silicon carbide single crystal is produced to minimize nitrogen concentration, then nitrogen concentration decreases, but production cost increases significantly
Solution Approach 1:
The patent converts the harmful effect of nitrogen impurities into a manageable condition by introducing aluminum dopant that compensates for nitrogen donors. Instead of expensively eliminating nitrogen to achieve high resistivity, the invention accepts nitrogen's presence and counteracts its harmful electrical effects through controlled aluminum doping, thereby achieving high resistivity at lower production cost.
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 maintains high electric resistivity and stable substrate potential across temperatures, preventing parasitic capacitance and output power degradation, ensuring consistent transistor performance even at elevated temperatures.
Implementation Method 1
a small amount of nitrogen that remains in the silicon carbide single crystal acts as a donor, and the activation rate of the nitrogen increases with an increase in temperature. Accordingly, the electric resistivity of the silicon carbide single crystal decreases with an increase in temperature
Implementation Method 2
a method of capturing electrons contributing to electric conduction by doping of a transition element... carriers activated by impurities or a crystal defect at room temperature or by an increase in temperature are temporarily captured by V, thereby preventing movement of the carriers to realize a high electric resistivity
Implementation Method 3
exhibits electric conduction by holes at room temperature
Data Source
AI summary
A silicon carbide single crystal has a positive correlation between a temperature and an electric resistivity in a range from room temperature to 400° C., has an electric resistivity of at least 1×107 Ω·cm in the range from room temperature to 400° C., exhibits electric conduction by holes while no significant electric conduction properties by electrons are observed regarding electric conduction at room temperature, and has a concentration of a transition element of 1×1017/cm3 or less.