Defect-enabled high crystallinity in 2D semiconductors and heterostructures

I present two 2D material systems where their crystallinities are paradoxically improved by defects during growth. First, I demonstrate that a new class of defect complex, interlayer Frenkel pairs, enhances the orientational epitaxy of transition metal dichalcogenides on hexagonal boron nitride, leading to experiments that achieve 95% consistency in orientational order by strongly suppressing inversion domains [1,2]. I will show how the stability of the defect complex originates from its electronic structure at the density functional theory level and discuss our recent extension to accelerated GW-level computations for defects. Second, I discuss our recent joint theory and experimental work on a 2D metal-semiconductor heterostructure hosting air-stable, crystalline 2D metals. Enabled by graphene defects in an initial graphene/SiC system, p-block metal atoms such as Ga, In, and Sn intercalate under graphene and bond covalently to the SiC beneath, forming lattice-matched 2D metals, as demonstrated by their calculated phase stabilities [3,4]. Based on first-principles calculations assisted by Wannier functions, I explain the presence of superconductivity in spite of the metals' free-electron-like electronic structure.

[1] F. Zhang*, Y. Wang*, C. Erb, K. Wang, P. Moradifar, V. H. Crespi, and N. Alem, Phys. Rev. B 99, 155430 (2019).
[2] X. Zhang, F. Zhang, Y. Wang, D. S. Schulman, T. Zhang, A. Bansal, N. Alem, S. Das, V. H. Crespi, M. Terrones, and J. M. Redwing, ACS Nano 13, 3341 (2019).
[3] N. Briggs et al. (2019), arXiv:1905.09962.
[4] B. Bersch et al. (2019), arXiv:1905.09938.