Impact of Molecular Dynamics Simulations on Research and Development of Semiconductor Materials
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.360
Impact of Molecular Dynamics Simulations on Research and Development of Semiconductor Materials Xiaowang Zhou Mechanics of Materials Department, Sandia National Laboratories, Livermore, CA 94550, U.S.A.
ABSTRACT
Atomic scale defects critically limit performance of semiconductor materials. To improve materials, defect effects and defect formation mechanisms must be understood. In this paper, we demonstrate multiple examples where molecular dynamics simulations have effectively addressed these issues that were not well addressed in prior experiments. In the first case, we report our recent progress on modelling graphene growth, where we found that defects in graphene are created around periphery of islands throughout graphene growth, not just in regions where graphene islands impinge as believed previously. In the second case, we report our recent progress on modelling TlBr, where we discovered that under an electric field, edge dislocations in TlBr migrate in both slip and climb directions. The climb motion ejects extensive vacancies that can cause the rapid aging of the material seen in experiments. In the third case, we discovered that the growth of InGaN films on ( ) surfaces suffers from a serious polymorphism problem that creates enormous amounts of defects. Growth on ( ̅ ) surfaces, on the other hand, results in single crystalline wurtzite films without any of these defects. In the fourth case, we first used simulations to derive dislocation energies that do not possess any noticeable statistical errors, and then used these error-free methods to discover possible misuse of misfit dislocation theory in past thin film studies. Finally, we highlight the significance of molecular dynamics simulations in reducing defects in the design space of nanostructures.
INTRODUCTION: Properties of semiconductor materials are extremely sensitive to crystallographic defects in the materials [1]. In optoelectronic devices, for example, line defects such as dislocations can cause rapid recombination of holes with electrons without converting the available energy into photons. This results in failure of the
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devices. The nonradiative recombination also uselessly heat the crystal, creating further property deteriorations. Unfortunately, practical semiconductors are often based on thin films with large lattice mismatches. For example, CdS/CdTe films can produce one of the lowest cost photovoltaic devices [2] but have a large lattice mismatch of more than 10%. InGaN/GaN films are critically needed for filling the “green gap” of the solid-state lighting devices [3,4], but this requires a large indium content that can also create a large lattice mismatch of 10% or above. Due to the large lattice mismatch, the materials alwa
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