Question regarding p-n junction DOS

[prasenjit]

Dear VASP community members,

I have a question regarding physics. We tried to do a calculation for an organic(p-type)-inorganic(n-type) interface for p-n junction photodiode. First we did a calculation for organic part, then the inorganic part and finally both together. All three of them were performed for the same unitcell size.

But while plotting DOS for the interface, the organic donor [p-type](as reported in literature) DOS shifts to lower energy, making it n-type.

I do not know where is the problem. Some literature suggests that part of the DOS (organic part) need to be shifted with respect to the vacuum level. How to do that?

I will be highly obliged if you can kindly give me your suggestions regarding this.

Thank you very much , with kind regards,
Prasenjit Roy
Electronic Structures of Materials
Radboud University
Nijmegen
+31 (0) 24 36 52805

[Neutrino]

Hi Prasenjit,

Aligning the DOS (or the bands) of interfacing semiconductors is not trivial and cannot be obtained directly from plotting the DOS of the interface. See an example here for two inorganic crystals:

http://pubs.acs.org/doi/abs/10.1021/jp306160c


Basically there is a bulk alignment term obtained from referencing the bulk DOS to the electrostatic potential in the respective cases , in addition to an interface term which is obtained by plotting the electrostatic potential in the interface system.

More insights can be found in the papers of C. Van de Walle from late 80's

Mostafa