How to build the graphene/semiconductor Schottky junction

[victor_liang]

Dear Staff,

  i am considering building graphene/semiconductor Schottky junction, but i did not note any publication of graphene/semiconductor Schottky contact. I read some tutorials on metal/graphene contact, but i do now know how to perform the optimization of built graphene/semiconductor contact. And i also do not know how to choose miller index of layer, which is best matching. Could you offer me some instructions or some useful publications, which i could follow? Thanks in advance.

Regards,
Victor

[Jess Wellendorff]

Dear Victor,

I think parts of the following two tutorials may help you in setting up a metal-semiconductor junction:
http://quantumwise.com/publications/tutorials/item/820-ni-silicide-si-interfaces
http://quantumwise.com/documents/tutorials/latest/GrapheneDevice/index.html/

The general recipe for setting up interfaces is this:
1) generate geometry optimized minimal unit cells of the two materials forming the junction.
2) create the two surfaces you want to face each other at the interface.
3) form the interface (using the Builders->Interface plugin), and relax that interface.

Step 3 is very important but may also be rather tedious. Please refer to our tutorial on this subject for some inspiration: http://quantumwise.com/publications/tutorials/item/878-geometry-optimization-of-interfaces. Unfortunately, the RigidBody functionality used in that tutorial are available from the upcoming 2015 versions of ATK and VNL only.

[victor_liang]

Thanks very much.

One key question is about the mirror orientation. Say, how to know the miller index (k,l,m) of a surface fits well with another surface? when i model the interface of two materials, for example graphene/MoS2, or graphene/Silicon? Is there any general rule to judge it? This problem is often encountered when i model interface. Thanks again.

[Jess Wellendorff]

You are right, this is a recurring problem in every junction simulation. I guess there are a few different ways to try to answer this question:
1) is experimental knowledge of the exposed surface facets available? That might be a good starting point.
2) when cleaved, a bulk crystal will usually try to expose the facet with lowest surface energy. This is often the (111) facet for fcc metals, the (100) facet for bcc, and (0001) for hcp. However, junctions in devices are usually created by depositing the two materials one at a time on an "inactive" substrate. The growth direction of the first junction material may therefore depend on the exposed surface of the substrate, and the second junction surface on the first one.... In the end, this is a complicated problem.
3) In most cases, one cannot know for sure the correct facet to use. But there may be general agreement that certain facets are more interesting/realistic than others, e.g. (100) for silicon.