What exactly are the quantities you're looking for when you say " determine CB and VB level ". Energy positions (of VBmax and CBmin)? With respect to what reference potential?

The quick answer is "it's not possible" for the simple reason that energies are only defined up to a constant (only energy differences matter).

In order provide you with a more constructive answer, you will need to suply some more context. What do you need those energy positions for? (An answer to this would hopefully clarify what energy reference is required.)

Dear Azami,

Some DFT papers assume the Fermi level is located at the valence band maximum (HOMO), leading to the energy position of conduction band minimum (LUMO) at 2.8 eV. This assumption is principally the same as Prof. Fauth has informed.

We can use UPS (ultraviolet photoemission spectra) for exactly determining the HOMO from the Fermi level. Then, we can predict LUMO from the observed bandgap.

Regards,

S. Muhammady

Dear Azami,

As a advice, the band gap is a strategy to determine only the photoactivation energy of semiconductors. First, you need to find the relative VB or CB position to sum this energy, and find the complete band structure of the studied material. Now, the VB and CB of the abovementioned semiconductors cannot be directly calculated. into the composite. You can use electrochemical techniques as Mott-Schottky analyses, where the semiconducting properties of the materials separately are independient from the frequency range during the measurements. Another form to establish the band structure is by XPS/UPS. Lastly, you can use the Mulliken electronegativity approach. It is better to find the band structure of each semiconductor separately, if you are going to find a suitable band alignment for charge carrier separation and transport, for instance. If you have some doubts, write to me at [email protected]

Best regards