Blue and red Stark shifts in single Si/SiO2quantum wells

The quantum-confined Stark shift (QCSS) of the ground and the first excited electron energy states in single Si/SiO2quantum wells is calculated. The QCSS for the ground state is always negative (blue), while the QCSS for the first excited state is positive, in general, but it can turn out to be negative when the electric field intensity becomes high enough. A remarkable reduction (∼50%) of the Stark shifts is obtained when the existence of nonabrupt interfaces as thin as 10 Å is taken into account. The nonabrupt interfaces can also change the sign of the Stark shift in the case of the excited states.