Defects of Silicon Carbide can bring about different natures, and these natures often need to be avoided. However, they have a positive effect in using. The representative utilization of the defects is a variety of point defects of silicon carbide.
What Are Point Defects of Silicon Carbide？
Point defects of silicon carbide refer to defects within the range of several atomic sizes in crystals, including:
- No atoms (Fig. 1): Vacancy. There are carbon vacancies Vc and silicon vacancies Vsi in silicon carbide;
- More atoms (Fig. 2): Interstitital. There are carbon interstitial Ic, silicon interstitial Isi, and impurity interstitial Ix;
- Atoms replaced (Fig. 3/4): Dislocation. There is carbon dislocation Csi, silicon dislocation Sic, impurity dislocation CX/Six in silicon carbide.
- More electronics: electronics;
- Missing electrons: holes.
Note: The big symbol indicates the actual situation of the location, and the small symbol indicates the original situation of the location.
Generally, the basis of semiconductor properties is based on the defects of electrons and holes, and we call these carriers. The three defects, vacancy, interstitital and dislocation, will lead to the defects of electrons and holes. For example, N-doped silicon carbide—N-type silicon carbide increases the number of electrons through the N dislocations, and increases the conductivity of silicon carbide. Therefore, general point defects of silicon carbide refer to the first three types.
Applications for Point Defects of Silicon Carbide:
In fact, articles are often published with a certain nature of point defects of silicon carbide, like color center. The color center is a point defect of silicon carbide, whose energy level is different from that of the host crystal, which makes the crystal have a color. Originally, a color center refers to a larger point defect formed by the combination of two or more simple point defects, but now they are all generalized. Direct ionization radiation may obtain multiple color centers, but the actual situation depends on the specific materials under the specific conditions.
The color centers that silicon carbide crystals produced now are as follows:
|Defect type||Crystal type||ZPL(nm)||D(GHz)||S|
It can be seen that the most typical combined defect of Si vacancy + electron has a spin of 3/2. The spin of a simple ion can be obtained by the electron orbit, for example, Cr3+ is 3d3, and the spin is 3/2. Due to the symmetry of the surrounding environment, the spin of color center cannot simply use the molecular orbitals to calculate. Si vacancy defects are surrounded by dangling bonds with four C atoms providing four electrons. In the absence of electron injection, the symmetry is D2d (mirror), instead of Td (tetrahedron), spin=0; inject one electron, spin=3/2.
|defects||M(µB)||Polarization energy Es-p(meV)
Common methods for introducing color centers:
- Vacuum heating in an atmosphere to make the atoms in the crystal form a gas and get vacancies;
- Heating in the atmosphere, so that the gas enters the crystal, and obtains interstitial and dislocation
- To obtain gap filling and dislocation, adding impurities during the synthesis process;
- High-energy radiation/injection (ultraviolet rays, X-rays, gamma rays, neutrons, electrons, ions) makes the atoms in the crystal form a gas and obtain vacancies;
- Irradiation/injection of high-energy rays (neutrons, electrons, ions) makes the particles enter the crystal and get interstitial and dislocation.
Introducing these color centers is actually introducing energy levels. The role of energy levels has been elaborated in semiconductors, such as controllable luminescence, controllable conduction, and so on. To realize the application of color center, energy levels should be introduced.
Under different magnetic fields, the color center energy level changes, which can be used for magnetic detection after the standard data is measured.
The color center energy level changes at different temperatures. After measuring the standard data, it can be used for temperature detection.
Light excitation, the color center spin changes. After measuring standard data, it can be used as a switch, that is, quantum computing.
After absorbing electrons, the changes in the energy level of the color center reflect the different positions of the radiated light. Such a reflection is photoluminescence(photoluminescence，PL, Fluorescence). Photoluminescence under the action of a magnetic field, light detection magnetic resonance(optically detected magnetic resonance，ODMR).
However, the color center is often unstable at room temperature, or the weak signal, manifesting as phonon broadening. The low temperature leads to a weakened phonon effect, obtaining photoluminescence spectrum lines, which are called zero phonon lines (ZPL).
Electrons (measured as 10^18cm2, 2MeV) injected into 21R-SiC (nitrogen concentration 5×10^16cm-3) can produce Si vacancy color centers.
Excited by 532nm light, the obtained 1-4 are zero phonon lines, and the high temperature is due to the broadening caused by phonons.
Temperature changes in different magnetic fields are as follows: