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Study of irradiation-induced point defects in silicon carbide

Silicon carbide (SiC) is a wide-bandgap semiconductor that crystallizes as a polytype with more than 200 different variations. Due to its “superior” physicochemical properties to silicon, it is a very promising material for electronic applications like nanoelectronic, power electronic, or sensors working under harsh conditions (high temperatures, corrosive or biological environment). This wide range of possible applications has motivated many studies on point defects, which play an important role in the electrical potential compensation of materials.

Very recent works have also shown that some point defects in SiC could be very favorable candidates for quantum information processing and spintronics, that are based on quantum properties of matter, such as superposition and entanglement of quantum states. In this domain, LSI is involved in a collaborative research project submitted to the French National Research Agency approval and entitled « Formation and Coherent Manipulation of Optically detectable Spins in Silicon Carbide ».

Equipment and Results

To study irradiation-induced point defects in SiC, the laboratory is equipped with PhotoLuminescence (in situ and ex situ PL) and Electronic Paramagnetic Resonance (ex situ EPR) experimental setups.

We have combined experimental results of low temperatures PL measurements with theoretical calculations to estimate the threshold displacement energy of silicon atoms in the cubic polytype (3C) of SiC. In order to do this, we followed the evolution of the silicon monovacancy PL signal as function of the electron beam energy of our Pelletron accelerator [1]. Annealing stages of point defects have also been highlighted at low temperature (20 K < T < 300 K) in this material by means of in situ PL experiments [2].

Using EPR under band-gap illumination, we showed experimental evidence of a defect centre in n-type 3C-SiC irradiated with 1-MeV electrons. This defects is diamagnetic (S=0) in its ground state and can be pumped into a paramagnetic (S=1, Ms=0) state by above-band-gap photon excitation, where it is detected by EPR absorption and emission transitions (Fig. 1) [3]. Further analyses are needed to identify the nature of this defect, that we assume it should be the silicon monovacancy in its neutral charge state (V0Si).

Figure 1 : First derivative of the EPR spectrum at 100 K with B perpendicular to [100] of the n-type 3C-SiC sample irradiated with 1-MeV electrons, (a) in the dark, and (b) under light illumination. (c) Integration of the spectrum.

We are currently developing an in situ EPR experiment that will be coupled to the beam line of our electron accelerator. This will allow us to analyze kinetics of irradiation-induced paramagnetic point defects in cubic (3C) and hexagonal (4H et 6H) polytypes of SiC in the low temperature domain (4 K – 300 K).

[1] J. Lefèvre, J.M. Costantini, S. Esnouf, and G. Petite, Silicon threshold displacement energy determined by photoluminescence in electron-irradiated cubic silicon carbide, J. Appl. Phys. 105(2), 023520 (2009)
[2] J. Lefèvre, J.M. Costantini, S. Esnouf, and G. Petite, Thermal stability of irradiation-induced point defects in cubic silicon carbide, J. Appl. Phys. 106, 083509 (2009)
[3] J. Lefèvre, J.M. Costantini, D. Gourier, S. Esnouf, and G. Petite, Characterization of a silicon-related defect detected by its excited triplet state in electron-irradiated 3C-SiC, Phys. Rev. B 83, 075201 (2011)