Stillinger-Weber potential for the II-VI elements Zn-Cd-Hg-S-Se-Te

Bulk and multilayered thin film crystals of II-VI semiconductor compounds are the leading materials for infrared sensing, γ-ray detection, photovoltaics, and quantum dot lighting applications. The key to achieving high performance for these applications is reducing crystallographic defects. Unfortunately, past efforts to improve these materials have been prolonged due to a lack of understanding with regards to defect formation and evolution mechanisms. To enable high-fidelity and high-efficiency atomistic simulations of defect mechanisms, this paper develops a Stillinger-Weber interatomic potential database for semiconductor compounds composed of the major II-VI elements Zn, Cd, Hg, S, Se, and Te. The potential's fidelity is achieved by optimizing all the pertinent model parameters, by imposing reasonable energy trends to correctly capture the transformation between elemental, solid solution, and compound phases, and by capturing exactly the experimental cohesive energies, lattice constants, and bulk moduli of all binary compounds. Verification tests indicate that our model correctly predicts crystalline growth of all binary compounds during molecular dynamics simulations of vapor deposition. Two stringent cases convincingly show that our potential is applicable for a variety of compound configurations involving all the six elements considered here. In the first case, we demonstrate a successful molecular dynamics simulation of crystalline growth of an alloyed (Cd${}_{0.28}$Zn${}_{0.68}$Hg${}_{0.04}$) (Te${}_{0.20}$Se${}_{0.18}$S${}_{0.62}$) compound on a ZnS substrate. In the second case, we demonstrate the predictive power of our model on defects, such as misfit dislocations, stacking faults, and subgrain nucleation, using a complex growth simulation of ZnS/CdSe/HgTe multilayers that also contain all the six elements considered here. Using CdTe as a case study, a comprehensive comparison of our potential with literature potentials is also made. Finally, we also propose unique insights for improving the Stillinger-Weber potential in future developments.

Figure 1

Cutoff of a typical SW potential pair function.

Figure 2

Atomic scale structure of the (Cd${}_{0.28}$Zn${}_{0.68}$Hg${}_{0.04}$)(Te${}_{0.20}$Se${}_{0.18}$S${}_{0.62}$)/ZnS layer obtained from molecular dynamics simulation. The pink shaded area highlights the initial ZnS substrate.

Figure 3

(a) Radial and (b) bond angle distribution functions obtained from the deposited film shown in Fig. 2.

Figure 4

Atomic scale structure of the HgTe/CdSe/ZnS multilayers obtained from molecular dynamics simulation. The pink shaded area highlights the initial ZnS substrate.

Figure 5

Comparison of cohesive energy for the Cd and Te elemental structures as predicted by DFT, BOP, literature SW, TR, and the new SW presented here (SW_new). Here, grap: graphene; dc: diamond cubic; gra: graphite; sc: simple cubic; bcc: body centered cubic; fcc: face centered cubic; hcp: hexagonal close packed; A8: γ-Se.

Figure 6

Comparison of (a) cohesive energies for several CdTe clusters and CdTe lattices, and (b) atomic volume for several CdTe lattices as predicted by DFT, BOP, literature SW, TR, and the new SW presented here (SW_new). Here, di: Cd-Te dimer; CdTeCd and TeCdTe: trimers; rhom: CdTeCdTe rhombus; fcs: face centered square; grap: graphene; B2: CsCl; B1: NaCl; wz: wurtzite; zb: diamond cubic.

Figure 7

Comparison of intrinsic defect energies as predicted by DFT, BOP, literature SW, TR, and the new SW presented here (SW_new). Here, $V_{\mathrm{Te}}$ and $V_{\mathrm{Cd}}$: Te and Cd vacancies, Cd${}_{\mathrm{Te}}$ and Te${}_{\mathrm{Cd}}$: Cd at Te and Te at Cd antisites, Cd${}_{\mathrm{i},\mathrm{Te}}$ and Te${}_{\mathrm{i},\mathrm{Cd}}$: Cd interstitial in Te tetrahedron and Te interstitial in Cd tetrahedron, Cd${}_{\mathrm{i},\langle 110\rangle }$ and Te${}_{\mathrm{i},\langle 110\rangle }$: Cd and Te dumbbell interstitial in the ⟨110⟩ direction, Cd${}_{\mathrm{i},\langle 100\rangle }$ and Te${}_{\mathrm{i},\langle 100\rangle }$: Cd and Te dumbbell interstitial in the ⟨100⟩ direction.