Excited states of defect lines in silicon: A first-principles study based on hydrogen cluster analogues

TL;DR

This study uses first-principles calculations to analyze the excited states of defect lines in silicon, revealing how inter-donor interactions influence their electronic properties and potential quantum computing applications.

Contribution

It provides a detailed theoretical analysis of excited states in donor clusters in silicon using advanced quantum chemistry methods, filling a gap in existing research.

Findings

Excited states dominate at short donor distances.

Ionic states are significant at intermediate distances.

Intra-donor excitations prevail at long distances.

Abstract

Excited states of a single donor in bulk silicon have previously been studied extensively based on effective mass theory. However, a proper theoretical description of the excited states of a donor cluster is still scarce. Here we study the excitations of lines of defects within a single-valley spherical band approximation, thus mapping the problem to a scaled hydrogen atom array. A series of detailed full configuration-interaction and time-dependent hybrid density-functional theory calculations have been performed to understand linear clusters of up to 10 donors. Our studies illustrate the generic features of their excited states, addressing the competition between formation of inter-donor ionic states and intra-donor atomic excited states. At short inter-donor distances, excited states of donor molecules are dominant, at intermediate distances ionic states play an important role, and at long distances the intra-donor excitations are predominant as expected. The calculations presented here emphasise the importance of correlations between donor electrons, and are thus complementary to other recent approaches that include effective mass anisotropy and multi-valley effects. The exchange splittings between relevant excited states have also been estimated for a donor pair and for a three-donor arrays; the splittings are much larger than those in the ground state in the range of donor separations between 10 and 20 nm. This establishes a solid theoretical basis for the use of excited-state exchange interactions for controllable quantum gate operations in silicon.