Defect-Related Properties and Growth Kinetics in 2D Layered Systems—Dopant-Dopant Interactions, Defect Electron-Phonon Coupling and Defect Spin Dynamics

Many functional properties and growth complications of chalcogenide films originate from their 2D form. In this talk we highlight defect-related properties and growth kinetics unique to 2D layered systems – some discovered in chalcogenide films, others anticipated. Specifically, we focus on dopant-dopant interactions, defect electron-phonon coupling, and defect spin dynamics in 2D films.<br/><br/>For dopant-dopant interaction, we show that rhenium doping of MoS2 is complicated by a strong dopant-dopant affinity at ~0.5 eV that could result in dopant clustering and deactivation. For example, a rhenium dopant pair deviates strongly from the classical hydrogen molecule analog by introducing deep levels through a pseudo Jahn-Teller distortion, leading to a strong affinity. The strong dopant-dopant affinity suggests that MoS2 may have an upper doping limit below that of conventional semiconductors, where donor deactivation kicks in at &lt; 1% dopant concentrations.<br/><br/>For electron-phonon coupling, we demonstrate the potential of finding defects with small Huang-Rhys (HR) factors in 2D systems. For example, the small HR factor of hBN boron vacancies of 0.54 (c.f. HR factor = 3.7 for diamond NV– triplet transition) is enabled by the availability of two types of antibonding orbitals, π and σ, only present in sp2 bonded solids. A small HR factor is a key performance metric for defect applications as single-photon emitters (SPE), directly related the degree of photon indistinguishability achievable. This discovery is enabled by a general SPE design principle we have developed from first principles, involving the degree of bonding-character similarity between excited and ground states.<br/><br/>For spin dynamics, we show that spin-orbit coupling matrix elements (SOCME) in 2D materials defects – a central ingredient in calculating intersystem crossing rates – can be much larger than those in conventional defects such as diamond NV– due to the availability of perpendicular orbitals. This finding is based on our recent plane-wave implementation of calculating SOCMEs at the density functional theory level, where efficient descriptors are also constructed based on easily computable Kohn-Sham orbital projections. We further show that our implementation avoids common inconveniences in model construction, cluster size convergence tests, edge passivation strategies (especially for chalcogenide systems), and calculating spin-vibration coupling.