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"K .Seino and A. Oshiyama, Appl. Surf. Sci. 561, 149927 (2021)

Energy barrier for surface diffusion
Surface diffusion

Potential energy surfaces(PESs)
Contour plot for atomic surfaces

a fundamental process of
epitaxial growthstep

Si adatom on Si(001):Brocks et al., Phys. Rev. Lett. (1990)

Contour plot
Useful to understandenergy barrier forsurface diffusion

For power semiconductors:
few studies

https://ja.wikipedia.org

15.07.21

SiC

 / K. Seino2Purpose and calculation
PESs !(#, %) for Si, C, and H adatoms for terrace and step onSiC(0001) surface
Gas sources of CVD growth of SiC: SiH4 and C3H8(H2 : carrier gas)
• Real-space DFT (density-functional theory) calculations
within the generalized gradient approximation (GGA-PBE)• Using RSDFT code (! 2011 Gordon Bell Prize for PeakPerformance)• 3C-SiC polytype, i.e., 3C-SiC(111) surface• Repeating slab model with 5 SiC bilayers• (1x1) surface reconstruction• Terrace: a rectagular (3x4) unit cell
Scale of the calculations:• Step edge: a rectagular (2x8) unit cell 100∼1050 atoms
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Si-faced SiC(0001) surfaces
3C-SiC(111) surface:equivalent to hexagonal(0001) surfaces

Top view
SiSi(buckled/upper)(2x1)

CSide view

Seino & Oshiyama, Appl. Surf. Sci. 561, 149927 (2021)
15.07.21

SiC

 / K. Seino

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PESs of terrace

SiSi(buckled/upper)C

Seino & Oshiyama, Appl. Surf. Sci. 561, 149927 (2021)

Adsorption sites: T4 and H3 sites (Si and C) , T1 (H)Energy barrier: 0.60-0.65 eV (Si), 1.45 eV (C),1.15-1.35 eV (H)
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SiC / K. Seino

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Calculated step formation energies
Step formation energy:
Constraint: .Si + .C = .SiC(bulk)! = #$%&' − #)*+% − ∑- .- Δ0-.- : chemical potential∆0- : difference of the number of atoms (2-th atomic species)
C-richSi-richConsidering two step directions:
5 direction
Si2, Si3, C1, C2: 121
SC: 115 0 direction

Si2 step:
most stable
Seino & Oshiyama, APEX
13, 015506 (2020) +Seino & Oshiyama, PRB
101, 195307 (2020)
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 / K. Seino

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Atomic structure near the step (Si2 step)
Si2 step:
12" 1 direction

SiSi(edge/upper)

CC(edge/upper)

Side view
Total charge density

Seino & Oshiyama, APEX
13, 015506 (2020) +Seino & Oshiyama, PRB
101, 195307 (2020)

Rebonding at thestep edges
Top view
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SiC

Side view / K. Seino

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PESs of step edges
Si2 step

Seino & Oshiyama, Appl. Surf. Sci. 561, 149927 (2021)

Ehrlich-Schwoebel effect in the inter-terrace diffusion?

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SiC

 / K. Seino8

Profiles of energies barriers at step edges

Seino & Oshiyama, Appl. Surf. Sci. 561, 149927 (2021)

The Ehrlich-Schwoebel effect is most prominent for the Si adatom withthe additional barrier of almost an eV for the inter-terrace diffusion. For
the C and H adatoms, the Ehrlich-Schwoebel barriers are small.
15.07.21

SiC

 / K. Seino

9Summary
We have performed first-principle total-energy calculations that
unviel the microscopic mechanism of diffusion on stepped Sifaced SiC surfaces.
• Identification of the diffusion pathways for Si, C, and H
adatoms and the corresponding energy profiles for both,on the surface terraces and near the surface steps• Different behavior of surface diffusion between “on theterrace” and “near the surface steps”⇒ Ehrlich-Schwoebel effectA computational approach in place of complicated experiments
Obtained results: basics to explore the microscopic
mechanism of epitaxial growth on SiC polar surface
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