Characterization and modelling of the ion-irradiation induced disorder in 6H-SiC and 3C-SiC single crystals

Abstract

6H-SiC and 3C-SiC single crystals were simultaneously irradiated at room temperature with 100-keV Fe ions at fluences up to 4x10 13 cm-2 (~0.7 dpa), i.e. up to amorphization. The disordering behaviour of both polytypes has been investigated by means of Rutherford backscattering spectrometry in the channelling mode and synchrotron X-ray diffraction. For the first time, it is experimentally demonstrated that the general damage build-up is similar in both polytypes. At low dose, irradiation induces the formation of small interstitial-type defects. With increasing dose, amorphous domains start to form at the expense of the defective crystalline regions. Full amorphization of the irradiated layer is achieved at the same dose (~0.45 dpa) for both polytypes. It is also shown that the interstitial-type defects formed during the first irradiation stage induce a tensile elastic strain (up to ~3.8%) to which is associated an elastic energy. It is conjectured that this stored energy destabilizes the current defective microstructure observed at low dose and stimulates the formation of the amorphous nanostructures at higher dose. Finally, the disorder accumulation has been successfully reproduced with two models (namely MSDA and DI/DS). Results obtained from this modelling are compared and discussed in the light of experimental data.

Interplay between atomic disorder, lattice swelling, and defect energy in ion-irradiation-induced amorphization of SiC

“…In this work, (001)-oriented 3C-SiC single crystals were irradiated with 100 keV Fe + ions at room temperature in the 4x10 13 -4x10 14 cm -2 fluence range [6], which corresponds to damage doses of 0.07 to 0.7 displacements per atom (dpa) at the damage peak, as determined with SRIM calculations [19] using the recommended threshold displacement energies of 20 eV and 35 eV for the C and Si sublattices, respectively [20][21]. The weighted average recoil spectra [22] were calculated from the SRIM data.…”

“…elastic) energy-loss is predominant (see e.g. [3,[5][6] and references therein). In this regime, both primary knock-on atoms (PKAs) produced by fast neutrons and incident ions collide with target nuclei, potentially leading to their permanent displacement through direct collisions or via collision cascades [7].…”

“…In the particular case of the amorphization kinetics in SiC, the 'Direct-Impact/Defect-Stimulated' model is the most employed [6,[13][14][15][16][17]. In this model, it is considered that the damage parameter p that is used to describe the irradiation damage consists of contributions from both amorphized and damaged-crystalline regions according to the relationship:…”

“…The stimulation of the amorphization process in ion-irradiated SiC has long been observed [6,[13][14][15][16][17]. Recently, molecular dynamics (MD) simulations of multiple Si cascades in SiC suggested that this stimulation process is ascribed to an enhanced defect clustering that provides a pathway to lower the energy of the defective SiC lattice [18].…”

Damage formation and recovery in Fe implanted 6H–SiC

“…As a violent process, implantation creates damage and as a binary compound the defects in both sublattices (Si and C) raise a multitude of defect configurations that need to be annealed. The defect production and annealing of the different SiC polytypes was studied by several groups, and it is reasonably well understood [9][10][11][12]. The short range nature of the covalent bonds makes SiC very radiation sensitive and easy to amorphize, and temperatures above 1000°C are necessary to promote defect recovery.…”