51
Figure 5.5: The structure formed with the layering of BaSnO3 and BaTaO2N.
represents BaSnO3 and represents BaTaO2N. Stacking is done along the
z-direction while x and y direction has the periodicity of the cubic perovskite
structure. The figure is taken from the Paper-4.
The calculation of the bandgap has been performed with the GLLB-SC
functional and the obtained bandgaps for BaSnO3 and BaTaO2N are 3.33
and 1.84 eV which are in good agreement with the measured experimental
bandgap of 3.1 and 1.9 eV for BaSnO3 and BaTaO2N respectively.112, 113
For comparison, the HSE06 calculated values of the bandgaps are 2.89 and
1.71 eV which is slightly lower than the GLLB-SC calculated bandgaps as
expected.
The calculated bandgap of heterostructure for different n and n is shown
in the Figure 5.6. The figure shows that the highest bandgap of 2.26 eV is
obtained for the stacking and the lowest value of 1.26 eV for 66 sequence.
The variation of the bandgap by 1 eV for different stacking sequences implies
a high degree of tunability of the bandgap by stacking different layers. The
wide variation in the bandgap can be understood in terms of the quantum
confinement and quantum tunneling effect. The sketch in the Figure 5.7 shows
how the local position of the conduction band edge moves downwards upon
increasing the number of and layers resulting to decreased confinement.
In order to understand the shift of the local conduction band edge on
changing the number of layers the location and nature of the CBM and VBM