Phonon-Enabled Carrier Transport of Localized States at Non-Polar Semiconductor Surfaces: A First-Principles-Based Prediction

Electron–phonon coupling can hamper carrier transport either by scattering or by the formation of mass-enhanced polarons. Here, we use time-dependent density functional theory-molecular dynamics simulations to show that phonons can also promote the transport of excited carriers. Using nonpolar InAs (110) surface as an example, we identify phonon-mediated coupling between electronic states close in energy as the origin for the enhanced transport. In particular, the coupling causes localized excitons in the resonant surface states to propagate into bulk with velocities as high as 10⁶ cm/s. The theory also predicts temperature enhanced carrier transport, which may be observable in ultrathin nanostructures

Solvent-Based Atomistic Theory for Doping Colloidal-Synthesized Quantum Dots via Cation Exchange

Electronic applications require the ability to dope a material with a controllable amount of impurities. However, current understanding of the doping mechanism in colloidal–synthesized quantum dots (QDs) is still limited. This is in contrast with bulk semiconductors for which first-principles-based theories have been well established. Using prototype CdSe as an example, here we propose an atomistic theory for the doping of colloidal-synthesized QDs. The key in our theory is the evaluation of atomic chemical potential inside the solution, whose range can deviate considerably from the bulk value due to the presence of solvent. This theory, coupled to first-principles calculations and ab initio molecular dynamics, is able to explain the difference of doping limit in Mn (or Co)-doped CdSe QDs and their bulk counterparts. It also explains the doping behavior of a number of other 3d transition-metal impurities in CdSe QDs in contrast with the solid case

Modular Approach for Metal–Semiconductor Heterostructures with Very Large Interface Lattice Misfit: A First-Principles Perspective

Realizing high-quality heteroepitaxy of a wide variety of films of very large lattice misfit, <i>f</i> ≥ 10%, with the substrate is a great challenge, but also a potential advancement, because the films may be made threading-dislocation-free as all the dislocations will be confined at the interface. In spite of the numerous experimental findings in the literature, first-principles theory for such systems is virtually nonexistent due to their intrinsic heterogeneity; namely, away from the interface, the film is strain free, but at the interface, not only strain but also misfit dislocation develop. Here, a modular approach is proposed to study such heterogeneous films by a combined first-principles and elasticity theory method to predict, for example, their epitaxial relationship. Four representative metal–semiconductor interfaces, Al(111)/Si(111), Cu(111)/Si(111), Cu(001)/Si(001), and CaF₂(111)/Ni­(001), are considered. By taking into account the chemical bonding information at the interface by first-principles theory, our results show good agreement with experiments. Moreover, by constructing the electron localization function (ELF) that utilizes the first-principles results, we are able to demonstrate the formation of interfacial covalent bonds between Si and metal atoms