Issue in Projected Local Density if states

[Deepakgate]

Dear Sir,

I have created Si/SiO2 interface as shown in figure attached, I am plotting the PLDOS. But facing some issues in it.
Like  in the example shown in following link regarding Si/Ag interface, there we can observe that in a bandgap of Silicon there is no states available (shown by black color), and this is true also.
http://docs.quantumwise.com/casestudies/ag_si_interface/ag_si_interface.html#projected-local-density-of-states

But in my case I am not able to see bandgap in silicon as all the energy levels seems to be occupied.
 I am attaching the structure and PLDOS image. Please tell me where I am doing wrong.

[Jess Wellendorff]

The device you have created is not semiconducting; it has non-zero transmission for all energies around the Fermi level. The reason is most likely that the periodicity of the silicion lattice in and near the two electrodes is destroyed. This is even visually very obvious. You need to re-create the device from scratch again with a few important changes: The electrodes and electrode extensions need to be longer in order to conserve the periodicity of the silicon lattice. Both electrodes should be at least 6 Å wide, and likewise for the electrode extensions. Please see the introductory tutorial on  ATK device calculations for more details: http://docs.quantumwise.com/tutorials/atk_transport_calculations/atk_transport_calculations.html