Influence of graded interfaces on the exciton energy of type-I and type-II Si/Si1-x Gex quantum wires

The exciton properties of Si/Si1-xGex cylindrical quantum wires (QWRs) are calculated using the variational method and taking into account the existence of an interface layer between the materials. We consider two possibilities for the conduction band lineup, type-I and type-II. Our numerical results show that an interfacial fluctuation of 15A° in a Si0.85Ge0.15 (Si0.70Ge0.30) type-I (type-II) wire of 50A° wire radius leads to an exciton energy blue shift of the order of 10 (10) meV.