The Relationship between the Microscopic Properties of Semiconducting Grain Boundaries and their Orientation

Abstract

The microscopic structure of a tilt and a twist boundary in germanium are explored using a state-of-the-art total energy calculation. The structure of the tilt boundary (Σ = 5 (310)) is found to be simple as it exhibits a well defined minimum energy structure, consistent with previous experimental and theoretical results on this and other tilt boundaries. The structure of the twist boundary (Σ = 5 (100)), however, is found to be very complex. The boundary bonds are distorted and weak, and their weakness makes the twist boundary exhibit a wealth of local energy minima. The different types of energy minima for the twist boundaries are identified and studied in some detail. We summarize the consequence of the orientation of the two crystal grains upon the microscopic structure of the boundaries, and speculate about future applications.

Computational studies of grain boundaries in covalent materials

“…A similar configuration was observed in Ge [100]. All these results can be understood from the morphology of the structural units [101,102,35]. For tilt boundaries, it is rather easy to construct stable structural units consisting of four-fold coordinated atomic rings, because the directions of dangling bonds on both grains are often parallel to a common plane and the period along the rotation axis is very short.…”

“…All these features are quite different from coincidence tilt boundaries. The boundary-energy values are several times larger than those of tilt boundaries [101].…”

Order and structural units in simulations of twist grain boundaries in silicon at absolute zero

“…Recently we have made a thorough investigation of the ⌺5 boundary and found that there are ordered, low-energy structures for this boundary, which were confirmed by firstprinciples simulations. 8 Our findings contradicted earlier simulations of twist boundaries, 5,6,[9][10][11][12][13] which did not find our low-energy ordered structures and which we attributed to inadequate sampling of configurational phase space.…”

“…Our results indicate that earlier simulations 5,6,[9][10][11][12][13] of this and most likely other twist boundaries in covalent semiconductors have failed to locate the global energy minima. There are two principal reasons.…”

“…First, only ⌬N = 0 and were considered prior to this work. Some authors 10 have noted that this restriction may be a serious limitation, but presumably for reasons of limited computing resources were unable to remove it. Second, MD quenches from the melt are required to be at least tens of nanoseconds in duration to sample adequately the configurational phase space, such as the propensity for the GB to facet.…”