Stability of undissociated screw dislocations in zinc-blende covalent materials from first principle simulations

– The properties of perfect screw dislocations have been investigated for several zinc-blende materials such as diamond, Si, β-SiC, Ge and GaAs, by performing first principles calculations. For almost all elements, a core configuration belonging to shuffle set planes is favored, in agreement with low temperature experiments. Only for diamond, a glide configuration has the lowest defect energy, thanks to an sp hybridization in the core. Several technologically interesting covalent materials are semiconductors or insulators with a zinc-blende crystalline structure. The most famous is silicon, extensively used in electronic devices. It is usually considered as a model for other materials with the same structure, and most of its properties are well known, thanks to an impressive number of dedicated studies. For instance, the plasticity of silicon has been largely investigated both experimentally and theoretically. At high temperature, silicon is ductile, and dislocations are dissociated into Shockley partials; since the dislocations are frequently aligned along the 〈110〉 dense directions, they mostly appear as 30◦ and 90◦ partials and slip in the so-called ’glide’ set of {111} planes (Fig. 1) [1]. Calculations have allowed to determine the core structure of partials [2–4], although the most stable configuration of the 90◦ is still not known with certainty [5–8]. At low temperature, in the brittle regime, surface scratch tests and confining pressure experiments have recently revealed the presence of undissociated dislocations, with screw, 60◦, 30◦ and 41◦ orientations [9, 10], so that very little investigation of these perfect dislocations recently have been reported. So far, theoretical studies have shown that the non-dissociated screw belongs to the ’shuffle’ set, though there has been a controversy about the most stable structure [11,12]. Other covalent materials with zinc-blende structure are expected to behave like silicon, at least at high temperature. Partial dislocations have been theoretically characterized for β-SiC (cubic 3C-SiC) [13–15], diamond [16–18], Ge [7,8,19], GaAs [20,21], and others [22,23]. However, it is not clear whether the results obtained at low temperature for silicon remained valid for those materials, and little is known on that subject. Experiments have shown that low temperature deformation of GaAs yields undissociated screw dislocations [24], like in silicon, and recent calculations by Blumenau et al focussed on perfect screw in diamond [15]. (∗) E-mail: [email protected]