Vanadium Compensated SiC Single Crystal Growth
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional SiC crystal growth methods struggle to achieve high-purity, vanadium-compensated SiC single crystals with reduced background nitrogen and boron concentrations, leading to suboptimal electronic properties and resistivity levels.
Innovation Solution
A sublimation growth method utilizing a reactive atmosphere with gaseous metal halides and hydrogen to chemically bind and remove residual nitrogen and boron impurities, followed by controlled doping with vanadium and nitrogen or boron to achieve fully compensated, semi-insulating SiC crystals of NU-type and PI-type.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional SiC crystal growth methods are used, then crystal growth is achieved, but background nitrogen and boron concentrations remain high leading to suboptimal electronic properties
Solution Approach 1:
The patent employs a reactive atmosphere containing gaseous metal halides (such as TaCl5, NbCl5, TaF5, or NbF5) and hydrogen during sublimation growth. This atmosphere chemically binds with nitrogen and boron impurities, effectively removing them from the crystal structure. The reactive atmosphere acts as a chemical filter that maintains ultra-low impurity concentrations throughout the crystal growth process, achieving background impurity levels below 10^15 atoms/cm³.
Solution Approach 2:
The patent utilizes controlled doping with vanadium at specific concentrations (10^16 to 10^18 atoms/cm³) to achieve full compensation of residual shallow donors and acceptors. By precisely controlling the vanadium doping level and the reactive atmosphere composition, the method optimizes the electronic properties and resistivity of the SiC crystals, transforming the material from conventional to semi-insulating with NU-type or PI-type characteristics.
2Reliability
If vanadium doping is introduced to achieve compensation, then resistivity increases, but precise control of compensation level becomes difficult
Solution Approach 1:
The patent implements a two-stage growth process with sequential doping. First, the reactive atmosphere removes background impurities during initial growth. Then, vanadium doping is introduced in a controlled manner to achieve full compensation. This staged approach with monitored impurity removal and controlled doping ensures precise achievement of the target compensation level and resistivity (exceeding 10^10 Ohm-cm), eliminating the trial-and-error nature of conventional single-stage doping.
3Quantity of substance
If sublimation growth is used to grow SiC crystals, then large crystals can be produced, but background impurity concentrations are difficult to reduce
Solution Approach 1:
The patent introduces gaseous metal halides as intermediary substances that mediate between the nitrogen/boron impurities and the crystal structure. These metal halides chemically bind with the impurities, forming volatile compounds that are removed from the growth zone. This intermediary mechanism enables effective impurity removal during sublimation growth, achieving ultra-pure crystals (below 10^15 atoms/cm³) while maintaining large crystal size and semi-insulating properties.
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 method effectively reduces background impurity concentrations, resulting in SiC crystals with enhanced resistivity and electronic properties, suitable for advanced semiconductor devices, with resistivity levels exceeding 10^10 Ohm-cm and activation energies between 0.78-1.5 eV.
Implementation Method 1
a reactive atmosphere in the growth ambient that removes donor and/or acceptor background impurities from the growth ambient
Implementation Method 2
gaseous metal halides and hydrogen to chemically bind and remove residual nitrogen and boron impurities
Implementation Method 3
Vanadium (V) produces two deep levels in the SiC bandgap - one deep donor at 1.5 eV above VB and one deep acceptor at 0.8 eV below CB. Deep acceptors can capture electrons, while deep donors can capture holes.
Implementation Method 4
sublimation growing a SiC single crystal on the SiC seed crystal via precipitation of sublimated SiC source material on the SiC seed crystal
Implementation Method 5
precipitation of sublimated SiC source material on the SiC seed crystal
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
In a crystal growth apparatus and method, polycrystalline source material and a seed crystal are introduced into a growth ambient comprised of a growth crucible disposed inside of a furnace chamber. In the presence of a first sublimation growth pressure, a single crystal is sublimation grown on the seed crystal via precipitation of sublimated source material on the seed crystal in the presence of a flow of a first gas that includes a reactive component that reacts with and removes donor and/or acceptor background impurities from the growth ambient during said sublimation growth. Then, in the presence of a second sublimation growth pressure, the single crystal is sublimation grown on the seed crystal via precipitation of sublimated source material on the seed crystal in the presence of a flow of a second gas that includes dopant vapors, but which does not include the reactive component.