Theoretical investigation of excitons in type-I and type-II Si/Si1-xGex quantum wires

This work presents a theoretical study of the excitonic properties of Si1-xGex cylindrical quantum wires surrounded by a Si matrix, considering two possibilities for the conduction band alignment, type I and type II. The effect of nonabrupt interfaces between these materials on the exciton energies is investigated: an interfacial region of 15 angstrom in a 50 angstrom wide Si0.85Ge0.15(Si0.7Ge0.3) type-I (type-II) quantum wire leads to an exciton energy blueshift of the order of 10 meV. The excitonic behavior under an applied magnetic field parallel to the wire axis is also studied: exciton energies in type-I wires are weakly affected, while for type-II wires, increasing the field causes the electron angular momentum to change almost periodically, giving rise to Aharonov-Bohm oscillations of the exciton ground state energy.