Mr. Yair Reichman MSc candidate Department
David Wang Auditorium, 3rd floor Dalia Meidan Bldg.
Modeling an interface between two materials with different crystallographic structures can be challenging, and there are plenty of motives to do so. In general, when an interface is formed, various complex processes can occur. There is a need to consider a variety of interface defects, such as point defects or dislocations, or, for example, phase transitions at the interface. These processes are either extremely hard or impossible to model in a periodic system (at least at the quantum scale).
Specifically, the more fundamental difficulty is the lattice mismatch problem. Since the description of crystalline materials is with periodic unit cells, it is necessary to construct a unit cell for the interface so that it can be described accurately, while different materials have different lattice constants. As a result, we need to multiply the unit cells of each material until they stack along with the interface in a way that allows us to describe the system with a single common unit cell (a supercell). Unfortunately, doing so will increase the number of atoms in the supercell to the extent that the calculation is impossible due to the computational cost. In other words, this “large supercell” approach is not feasible.
A more realistic approach is to take an average of two lattice constants (of material A and B) and compress/expand the unit cell of individual materials to get one single lattice
parameter; afterward, we can relax the supercell’s lattice constant to achieve the minimal energy of the interface.
We will present results relating to several binary heterostructure interfaces of zinc-blende semiconductors. The calculations were conducted upon structures with strain induced by lattice parameter mismatch. We will point out some trends concerning the band gaps of the semiconductor heterostructures near and far from the mismatched interface. Furthermore, in the last part of the talk, we will present some results regarding charge transport dynamics through the interfaces.
B.Sc. in materials science and engineering and chemistry, Technion.