Defect engineering in SiC for quantum spintronics

Silicon carbide (SiC) is a wide band-gap semiconductor (6H-SiC with Eg of 3.05 eV) with unique mechanical, electrical, and thermal properties, which make the material suitable for many demanding applications in extreme conditions, such as high temperature, high power, high frequency and high radiation exposure. Two recently reported phenomena related to the defects in SiC are opening the door for semiconductor spintronics and quantum computing:

(1) Room temperature ferromagnetism has been observed in neon ion or neutron irradiated both 4H- and 6H-SiC [1, 2]. This is somehow surprising since the materials are transition-metal free, which also gives rise to the term ‘‘d0 ferromagnetism’’.
(2) Some defect (including the neutral carbon–silicon divacancy) spin states in 4H-SiC can be optically addressed and coherently controlled up to room temperature [3]. These defect spin states are ideal information carriers for quantum computing.

Particle irradiation provides a way to engineer defects in crystalline materials regarding the defect concentration and type. In this contribution, we made a comprehensive investigation on the structural and magnetic properties of ion implanted and neutron irradiated SiC samples. In combination with X-ray absorption spectroscopy, high-resolution transmission electron microscopy and first-principles calculations, we try to understand the mechanism in a microscopic picture.

For neon or xenon ion implanted SiC, we identify a multi-magnetic-phase nature [2, 4]. The magnetization of SiC can be decomposed into paramagnetic, superparamagnetic and ferromagnetic contributions. The ferromagnetic contribution persists well above room temperature and exhibits a pronounced magnetic anisotropy. By combining X-ray magnetic circular dichroism and first-principles calculations, we clarify that p-electrons of the nearest-neighbor carbon atoms around divacancies are mainly responsible for the long-range ferromagnetic coupling [5]. Thus, we provide a correlation between the collective magnetic phenomena and the specific electrons/orbitals.

For neutron irradiated SiC, we observe a strong paramagnetism, scaling up with the neutron fluence [6]. A weak ferromagnetic contribution only occurs in a narrow fluence window or after annealing. The interaction between the nuclear spin and the paramagnetic defect can effectively tune the spin-lattice relaxation time (T1) as well as the nuclear spin coherent time (T2). For the sample with the largest neutron irradiation fluence, T1 and T2 are determined to be around 520 s and 1 ms at 2K, respectively.

[1] Y. Liu, et al., Phys. Rev. Lett. 106, 087205 (2011).
[2] L. Li, et al., Appl. Phys. Lett. 98, 222508 (2011).
[3] W. Koehl, et al., Nature 479, 84 (2011).
[4] Y. Wang, et al., Phys. Rev. B 89, 014417 (2014).
[5] Y. Wang, et al., Scientific Reports, 5, 8999 (2015).
[6] Y. Wang, et al., Phys. Rev. B 92, 174409 (2015).