Atchara Punya Jaroenjittichai

Formation energies and chemical potential diagrams of II-Ge-N2 semiconductors

ABSTRACT III-Nitride wide band gap semiconductors are well known for optoelectronic and electronic applications. They however have disadvantages, for example, the high cost of Indium, difficulties of p-type doping and phase separation in their alloys. In this work, the novel II-Ge-N2 semiconductors that are related to III-N by replacing the group-III with a group-II (Mg and Cd) and a group-IV (Ge) are investigated. The lattice parameters of the II-Ge-N2 are predicted by a full potential linear muffin-tin orbital (FP-LMTO) approach within the generalized gradient approximation (GGA). The results are also compared with those of ZnGeN2. Furthermore, the formation energies of the new materials and their competing compounds, such as Zn3N2, Mg3N2, Cd3N2 and Ge3N4, are calculated from the constituent elements. The chemical potential diagrams for stability, which are constructed from the calculated formation energies, facilitate us to determine the allowed ranges of the chemical potentials of the elements where the compounds are stable at zero temperature and pressure.ABSTRACTIII-Nitride wide band gap semiconductors are well known for optoelectronic and electronic applications. They however have disadvantages, for example, the high cost of Indium, difficulties of p-type doping and phase separation in their alloys. In this work, the novel II-Ge-N2 semiconductors that are related to III-N by replacing the group-III with a group-II (Mg and Cd) and a group-IV (Ge) are investigated. The lattice parameters of the II-Ge-N2 are predicted by a full potential linear muffin-tin orbital (FP-LMTO) approach within the generalized gradient approximation (GGA). The results are also compared with those of ZnGeN2. Furthermore, the formation energies of the new materials and their competing compounds, such as Zn3N2, Mg3N2, Cd3N2 and Ge3N4, are calculated from the constituent elements. The chemical potential diagrams for stability, which are constructed from the calculated formation energies, facilitate us to determine the allowed ranges of the chemical potentials of the elements where th...

DFT calculations of strain and interface effects on electronic structures and magnetic properties of L10-FePt/Ag heterojunction of GMR applications

In this work, density functional theory (DFT) was employed to investigate the effect of strain and interface on electronic structures and magnetic properties of L10-FePt/Ag heterojunction. Two possible interface structures of L10-FePt(001)/Ag(001), that is, interface between Fe and Ag layers (Fe/Ag) and between Pt and Ag layers (Pt/Ag), were inspected. It was found that Pt/Ag interface is more stable than Fe/Ag interface due to its lower formation energy. Further, under the lattice mismatch induced tensile strain, the enhancement of magnetism for both Fe/Ag and Pt/Ag interface structures has been found to have progressed, though the magnetic moments of “interfacial” Fe and Pt atoms have been found to have decreased. To explain this further, the local density of states (LDOS) analysis suggests that interaction between Fe (Pt) and Ag near Fe/Ag (Pt/Ag) interface leads to spin symmetry breaking of the Ag atom and hence induces magnetism magnitude. In contrast, the magnetic moments of interfacial Fe and Pt atoms reduce because of the increase in the electronic states near the Fermi level of the minority-spin electrons. In addition, the significant enhancements of the LDOS near the Fermi levels of the minority-spin electrons signify the boosting of the transport properties of the minority-spin electrons and hence the spin-dependent electron transport at this ferromagnet/metal interface. From this work, it is expected that this clarification of the interfacial magnetism may inspire new innovation on how to improve spin-dependent electron transport for enhancing the giant magnetoresistance (GMR) ratio of potential GMR-based spintronic devices.In this work, density functional theory (DFT) was employed to investigate the effect of strain and interface on electronic structures and magnetic properties of L10-FePt/Ag heterojunction. Two possible interface structures of L10-FePt(001)/Ag(001), that is, interface between Fe and Ag layers (Fe/Ag) and between Pt and Ag layers (Pt/Ag), were inspected. It was found that Pt/Ag interface is more stable than Fe/Ag interface due to its lower formation energy. Further, under the lattice mismatch induced tensile strain, the enhancement of magnetism for both Fe/Ag and Pt/Ag interface structures has been found to have progressed, though the magnetic moments of “interfacial” Fe and Pt atoms have been found to have decreased. To explain this further, the local density of states (LDOS) analysis suggests that interaction between Fe (Pt) and Ag near Fe/Ag (Pt/Ag) interface leads to spin symmetry breaking of the Ag atom and hence induces magnetism magnitude. In contrast, the magnetic moments of interfacial Fe and Pt at...

First-principles investigation of a novel organic-inorganic strontium halide perovskites and CH3NH3Pb1-xSrxI3 solid solution

ABSTRACT In this work, we used the density functional theory to predict the stability of CH3NH3SrI3 by constructing a chemical potential diagram. We found that there are stability regions of CH3NH3SrI3 for tetragonal and orthorhombic structures. The GW approximation including spin-orbit coupling (SOC) predicted that CH3NH3SrI3 is a wide band gap semiconductor. In addition, the structural and optical properties as a function of strontium concentration (x) in CH3NH3Pb1-xSrxI3 were also investigated and it displays the linear dependence on concentration. The results indicate the tunability and its potential as an alternative for using lower concentration of lead in organic-inorganic halide perovskite.