ABSTRACT
Superlattices made of alternating blocks of the phase change compound Sb[Formula: see text]Te[Formula: see text] and of TiTe[Formula: see text] confining layers have been recently proposed for applications in neuromorphic devices. The Sb[Formula: see text]Te[Formula: see text]/TiTe[Formula: see text] heterostructure allows for a better control of multiple intermediate resistance states and for a lower drift with time of the electrical resistance of the amorphous phase. However, Sb[Formula: see text]Te[Formula: see text] suffers from a low data retention due to a low crystallization temperature T[Formula: see text]. Substituting Sb[Formula: see text]Te[Formula: see text] with a phase change compound with a higher T[Formula: see text], such as GeTe, seems an interesting option in this respect. Nanoconfinement might, however, alters the crystallization kinetics with respect to the bulk. In this work, we investigated the crystallization process of GeTe nanoconfined in geometries mimicking GeTe/TiTe[Formula: see text] superlattices by means of molecular dynamics simulations with a machine learning potential. The simulations reveal that nanoconfinement induces a mild reduction in the crystal growth velocities which would not hinder the application of GeTe/TiTe[Formula: see text] heterostructures in neuromorphic devices with superior data retention.
ABSTRACT
ß-FeSi2 has been doped with Boron via a novel and cost-effective chemical reduction of the glassy phase of [(Fe2O3 + 4SiO2 + B2O3 + FeBO3 + Fe2SiO4)] using Mg metal at 800 °C. Doped ß-FeSi2 has been investigated via extensive characterization and detailed analysis using first-principles calculations. The reduction in the d-spacing as can be observed from the XRD peak shift as well as the blue shift of the ß-Raman line along with the right shift of Si and Fe 2p peaks indicate the B doping. The Hall investigation basically demonstrates p-type conductivity. Hall parameters were also analyzed using thermal mobility and dual-band model. The temperature profile of RH demonstrates the contribution of shallow acceptor levels at low temperatures, whereas the deep acceptor level contributes at high temperatures. Dual-band investigation reveals a substantial increase in the Hall concentration with B doping due to the cumulative contribution of both deep and shallow acceptor levels. The low-temperature mobility profile exhibits phonon and ionized impurity scattering just above and below 75 K, respectively. Moreover, it demonstrates that holes in low-doped samples can be transported more easily than at higher B doping. From density functional theory (DFT) calculations, the origin of the dual-band model has been validated from the electronic structure of ß-FeSi2. Further, the effects of Si and Fe vacancies and B doping on the electronic structure of ß-FeSi2 have also been demonstrated. The charge transfer to the system due to B doping has indicated that an increase in doping leads to higher p-type characteristics.
ABSTRACT
Hybrid halide perovskites frequently undergo structural expansion due to various stimuli, significantly affecting their electronic properties and in particular their charge carrier dynamics. It is essential to atomistically model how geometric changes modify electronic characteristics that are important for applications such as light harvesting and lighting. Using ab initio simulations, here we investigate the structural dynamics and optoelectronic properties of FAPbI3 under tensile strain. The applied strain leads to elongation of the Pb-I bonds and a decrease in the level of PbI6 octahedral tilting, which manifests as blue-shifts in band gaps. Nonadiabatic molecular dynamics simulations further reveal that charge carrier recombination rates moderately decrease in these expanded lattices. The complex influence of lattice dynamics on electron-phonon scattering results in a longer carrier lifetime, which is advantageous for efficient solar cells. By providing detailed information about the structure-property relationships, this work emphasizes the role of controlled lattice expansion in enhancing the electronic functionalities of hybrid perovskites.