Dear Satya
Like Giovanni, I also don't know why you don't obtain what you expect.
But I want to offer my own penny to the discussion.
1) Due to the well known effect of delocalization errors in GGA-DFT,
the band gap of Si is generally reduced to around 0.6 eV. The
reduction involves both the lowering of the conduction band potential
and the raising of the valence band potential. In the case of ZnO you
have a strongly curved conduction band around the minimum at Gamma,
which is not affected by delocalization errors, and a very problematic
valence band, in which the interaction between the narrow O 2p and Zn
3d contributions may raise the valence band maximum by more than 2 eV,
shrinking the band gap to less than 1 eV in bulk ZnO.
2) First of all, therefore, I would check *in the same supercell* if
isolated Si and isolated ZnO slabs envisage a metallic character of
the junction due to the unsymmetrical band gap underestimation of the
two parts.
3) The most stable ZnO surface is (10-10), not 0001 (or its 000-1
counterpart having reverse polarity). The polar surfaces of ZnO are
tricky to simulate as slabs due to the strong polarity of the Zn-O
bond. In the past, I obtained some weird layered hexagonal structure
similar to BN! I suppose that the choice of (0001) is purposeful. If
it is not, try to reconsider your choice.
4) Such a strongly polar surface in contact with a non-polar Si
surface may induce a huge interfacial charge transfer, even enhanced
by delocalization errors mentioned above, or can lead to significant
shifts of band edges, yielding a metallic character of the
semiconductor junction.
HTH
Giuseppe
Quoting Satyasiban Dash ph19d005 <[email protected]>:
Yes . Thank you for the clarification. I am trying to match (0001) surface.
But I have observed upon relaxing ZnO loosing its symmetry and this may be
due to the polar surfaces but experimentally we do observe a band gap. I
have also tried dipole correction but results are same. But if I remove Si
its giving a gap. Is there anyway to reproduce it with Si (001).
On Thu, 28 Apr, 2022, 4:55 pm Giovanni Cantele, <
[email protected]> wrote:
Dear Satya,
it is not that easy (at least for me) to provide an answer to your
question using the data you have provided. Maybe the output files (of scf
and bands) and a plot of your band structure might help to infer if there
is any issue in your calculation.
However, before wondering whether you get a metal whereas experiments
measure a gap, you should also check that you are simulating a system that
is as close as possible to the experimental one (in terms of thickness
and/or surface orientation of both ZnO and Si, and so on). As far as the
atomic positions are concerned, they look reasonable. It seems (if I’m not
wrong) that you are trying to match a Si(100) surface with a ZnO(0001)
surface, aren’t you? Is this what you expect?
Giovanni
--
Giovanni Cantele, PhD
CNR-SPIN
c/o Dipartimento di Fisica
Universita' di Napoli "Federico II"
Complesso Universitario M. S. Angelo - Ed. 6
Via Cintia, I-80126, Napoli, Italy
e-mail: [email protected] <[email protected]>
Phone: +39 081 676910
Skype contact: giocan74
ResearcherID: http://www.researcherid.com/rid/A-1951-2009
Web page: https://sites.google.com/view/giovanni-cantele/home
On 28 Apr 2022, at 07:09, Satyasiban Dash ph19d005 <
[email protected]> wrote:
Dear Users
I have been trying to calculate a heterostructure with a slab model. I
have followed most of the examples given in the forum and tried it still I
am getting a metallic band structure. I have used the K-path generation
tool provided in "material project" website to generate k-path. I have
given the scf and bands.in file as attached files. Please have a look.
Experimentally this system has a wide band gap.
Thanks.
Satya
Research Scholar
IIT Madras.
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