Abstract
Heteroepitaxial films of Ge on Si(001) are receiving wide attention due to several possible applications in micro- and opto-electronics. Understanding the dynamic behavior of linear defects, such as dislocations, is key. They are unavoidably present in such systems due to the lattice mismatch between the two materials, and can directly influence devices performances. It has been experimentally demonstrated more than fifteen years ago that a suitable choice of the growth parameters allows for the formation of a nicely ordered net of 90^{circ } dislocations at the Ge/Si interface, improving the overall film quality and strain relaxation uniformity. Atomic-scale details on the set of mechanisms leading to such an outcome are however still missing. Here we present a set of classical molecular dynamics simulations shedding light on the full set of microscopic processes driving to the experimentally observed array of linear defects. This includes simple gliding of 60^{circ } dislocations and vacancy-promoted climbing and gliding. The importance of the particular experimental conditions, involving a low-temperature stage followed by an increase in temperature, is highlighted.
Highlights
IntroductionDue to its compatibility with standard silicon (Si) technology and to several superior properties with respect to Si, Germanium (Ge) has attracted widespread attention
Experiments evidenced the presence of edge dislocations at the interface, with their density increasing at the expense of 60◦ dislocations when a high temperature or annealing step follows the low-temperature deposition[21–24,27]
All simulation results presented in this work were obtained in the framework of classical molecular dynamics as implemented in the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS)[36]
Summary
Due to its compatibility with standard silicon (Si) technology and to several superior properties with respect to Si, Germanium (Ge) has attracted widespread attention. As three-dimensional growth, allowing for partial relaxation of the lattice mismatch[16,19,20], is unsuitable for most applications, out-of-equilibrium conditions are typically exploited to grow flat films These can be achieved by lowering the growth temperature and/or by using high deposition r ates[21–24]. Under such conditions, the lattice mismatch is solely released via plastic relaxation following dislocation nucleation. Experiments evidenced the presence of edge dislocations at the interface, with their density increasing at the expense of 60◦ dislocations when a high temperature or annealing step follows the low-temperature deposition[21–24,27]. Two different questions are still under discussion: (i) How are 90◦ dislocations formed? (ii) How is lateral ordering of dislocation at the interface reached?
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