Molecular Dynamics Simulations of CdTe / CdS Heteroepitaxy - Effect of Substrate Orientation

Abstract

Molecular dynamics simulations were used to catalogue atomic scale structures of CdTe films grown on eight wurtzite (wz) and zinc-blende (zb) CdS surfaces. Polytypism, grain boundaries, dislocations and other film defects were detected. Dislocation lines were distributed in three distinct ways. For the growths on the wz {0001} and zb {111} surfaces, dislocations were found throughout the epilayers and formed a network at the interface. The dislocations within the films grown on the wz {1 100}, wz {112 0}, zb {1 10}, zb {010}, and zb { 1 } surfaces formed an interface network and also threaded from the interface towards the film's surface. In contrast, the growth on the zb {112 } surface only had dislocations localized to the interface. This film exhibited a different orientation from the substrate to reduce the lattice mismatch strain energies, and therefore, its misfit dislocation density. Our study indicates that the substrate orientation could be utilized to modify the morphology of dislocation networks in lattice mismatched multi-layered systems.

Molecular Dynamics Study of High Symmetry Planar Defect Evolution during Growth of CdTe/CdS Films

“…The substrates were created using lattice parameters of a ZB = 0.5847 and 0.6491 nm for CdS and CdTe, respectively. These lattice parameters were obtained from time averaged MD simulations of bulk single crystals at 300 K 44,48 and are in excellent agreement (less than 1% difference) with experimental values 51 and molecular statics calculations. 44 Once the initial atomic structure was created, the equilibrium substrate dimension was achieved employing a careful three-step relaxation procedure.…”

“…In addition, MD simulations allow virtual experiments that isolate external factors and enable rapid systematic exploration in a wide range of growth parameters. For instance, based on a II–VI interatomic potential database, − MD simulations have been successfully used to discover and correct issues of the traditional misfit dislocation theory, design defect free, nanostructured CdTe/CdS solar cells, and catalogue the atomic scale structures of CdS homoepitaxy and CdTe/CdS heteroepitaxy on several substrate surfaces.…”

Molecular Dynamics Study of Heteroepitaxial Growth of HgCdTe on Perfect and Dislocated (211)B CdZnTe Substrates

“…Previous studies − ,− would increase the thickness of the thermostat region during vapor deposition to maintain a constant temperature throughout the material. This was found to be unnecessary here as the growth rates and incident kinetic energy of vapor atoms used were low enough for the grown MCT to maintain the same temperature as the thermostat region during vapor deposition.…”

“…Numerous molecular dynamics (MD) studies on the crystal growth of semiconductors by vapor deposition have been conducted for various systems. Some examples include growth of microcrystalline and amorphous Si on hydrogen-terminated Si substrates, , InAs/InAs 0.5 Sb 0.5 type-II superlattices on GaSb substrates, homoepitaxy of GaAs, , heteroepitaxy of InGaN on GaN substrates, − and heteroepitaxy of CdTe on CdS substrates. − These studies generally involve varying the conditions of the substrate (temperature, orientation, and presence of defects) and the vapor atoms (velocity, angle, growth rate, and flux ratio between different atom types) and observing their impact on epilayer growth.…”

Molecular Dynamics Calculations of Grain Boundary Mobility in CdTe

“…This potential is chosen because it both captures accurately the experimental atomic volumes, cohesive energies, and elastic properties of CdTe [12], and predicts the crystalline growth of II-VI compounds correctly [13]. Since the potential has been widely used to study grain structures in CdTe/CdS systems [3,13,14,15,16], knowledge of GB mobilities using the same potential has an additional advantage for comparing to previous studies.…”