Hole states in vertically coupled double Ge/Si quantum dots

Using a six-band k.p formalism we investigated the single-particle hole states in the double quantum dots made of two identical, vertically stacked, Ge/Si nanoclusters. The elastic strain due to the lattice mismatch between Ge and Si was included into the problem via Bir-Pikus Hamiltonian. As consequence of inhomogeneous strain distribution, the symmetry of states is breaking. The splitting of bonding state, @s"S, from antibonding one, @s"A"S, is not symmetric, the average hole binding energy decreases with decreasing interdot separation. The change of interdot separation t"S"i causes crossing between the energy levels corresponding to @s"S and @s"A"S orbitals. As a result, at t"S"i@?4nm, the antibonding state @s"A"S becomes the ground state of the system, replacing the @s"S state.