Radiation-induced mobility of small defect clusters in covalent materials

Abstract

Although defect clusters are detrimental to electronic and mechanical properties of semiconductor materials, annihilation of such clusters is limited by their lack of thermal mobility due to high migration barriers. Here, we find that small clusters in bulk SiC (a covalent material of importance for both electronic and nuclear applications) can become mobile at room temperature under the influence of electron radiation. So far, direct observation of radiationinduced diffusion of defect clusters in bulk materials has not been demonstrated yet. This finding was made possible by low angle annular dark field (LAADF) scanning transmission electron microscopy (STEM) combined with non-rigid registration technique to remove sample instability, which enables atomic resolution imaging of small migrating defect clusters. We show that the underlying mechanism of this athermal diffusion is ballistic collision between incoming electrons and cluster atoms. Our findings suggest that defect clusters may be mobile under certain irradiation conditions, changing current understanding of cluster annealing process in irradiated covalent materials. Main textDefect clusters can form in covalent materials during ion implantation (e.g., in semiconductor applications) [1,2] or during irradiation (e.g., in nuclear reactor applications) [3][4][5][6]. Accumulation of such clusters is highly detrimental to electronic, optical, and mechanical properties of these materials [1,4,7]. While point defects can often be eradicated by mutual recombination or diffusion to defect sinks, clusters of defects in covalent materials are known to be immobile and resist annealing because of their high energy barriers to migration [8,9]. For SiC specifically, accelerated molecular dynamics (MD) simulations have shown that the barrier to migration of clusters as small as just three C interstitials is ~4.3 eV [8], which means that these clusters are immobile below 1,200 K on typical experimental annealing time scales (i.e., 1 hour whereas the cluster performs less than 1 hop/day). Such high barriers explain why models of defect evolution in SiC have assumed clusters to be immobile even at elevated temperatures (e.g., Ref. [10,11]) and why the nature of such clusters, their resistance to high-temperature annealing, and their effects on opto-electronic properties have been a subject of many discussions in the semiconductor literature [12,13].In this letter, we report a direct observation of interstitial clusters diffusion in bulk SiC under the influence of electron radiation at room temperature. Although it is known that in metals

Evolution of small defect clusters in ion-irradiated 3C-SiC: Combined cluster dynamics modeling and experimental study

“…For instance, Jiang et al [63] used accelerated molecular simulations to show that migration barrier for C tri-interstitial cluster is ~4.12 eV, which means that this cluster will be immobile on experimental time scales up to temperatures of 1,200K (at these temperatures the cluster performs ~ 1 hop/day). However, there is recent experimental evidence that under some irradiation conditions clusters in SiC can undergo radiation-induced diffusion due to ballistic collision of the incoming particles with cluster atoms [26]. This phenomenon has been discovered in SiC only recently and the effective migration barriers of clusters during irradiation of SiC are unknown.…”

“…(a) shows a low angle annular dark field (LAADF) STEM image of Kr-irradiated 3C-SiC with the viewing direction along the <110> axis. Compared to high-angle annular dark field (HAADF) STEM images, LAADF images emphasize strain contrast, making small BSDs more visible[26]. The bright spots are the Si atom columns, as shown in the inset.…”

Three-Dimensional Imaging of Single La Vacancies in LaMnO 3

“…The energy transferred from an incident electron to an atom in the sample, ′ , is given by, [37] ′ 1.02 496…”

Optimization of self-interstitial clusters in 3C-SiC with genetic algorithm

“…Positive values of these quantities imply that the binding of an interstitial or a smaller cluster to another cluster is favored. Thus a cluster with positive binding energies is expected to grow under irradiation in the presence of a supersaturation of interstitials or mobile small clusters [46]. All compositions of SIA clusters reported in this study, except Si4, were found to have positive binding energies.…”