Atomic-scale lattice defects, such as, e.g., vacancies, substitutional atoms, impurity atoms etc, are an unavoidable by-product in the fabrication of two-dimensional materials and affect a wide range of material properties ranging from carrier transport to exciton dynamics. Often, the atomic nature of the most prevalent type of defects can be inferred from STM studies which provide insight into the atomic structure and the electronic properties of defect sites.<br/><br/>This talk, I will introduce a first-principles method for the modeling of realistic defects and their impact on electron dynamics and transport in disordered two-dimensional materials. The method is based on DFT + supercell modeling of the defects, which allows for a microscopic description of the perturbing defect potential and its impact on electron scattering. In combination with T-matrix formalism, we investigate the effect of atomic defects on (i) the spectral properties and quasiparticle scattering, (ii) in-gap bound defect states, and (iii) carrier transport and mobilities in various 2D materials. Among other things, I will discuss a concomitant break-down of the widely used Born approximation for scattering by general atomic defects in 2D materials.<br/><br/>The last part of the talk will focus on electron and hole transport in the family of monolayer transition metal dichalcogenides (TMDs). Here, the break-down of the Born approximation for the commonly observed atomic-vacancy defects manifests itself in a strong energy (or carrier density) dependence of the carrier mobility. However, the predicted density dependence is in contradiction with many experimental observations, which we attribute to charging of in-gap bound defect states. For defects which do not give rise to in-gap bound states, we hence predict a qualitatively different behavior as well as much higher values of the carrier mobility. As I will demonstrate, recent experiments on p-doped WSe2 support this interpretation, and at the same time points to strongly material, defect and doping (p vs n) dependent transport properties in monolayer TMD devices.

First-principles modeling of electron dynamics and transport in disordered two-dimensional materials

2019 Spring National Meeting

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