Investigation of defects in structures based on BP/Si heterojunction

In this work the properties of the BP/Si heterojunction interface were investigated by capacitance methods, the deep levels transient spectroscopy method and admittance spectroscopy. Admittance spectroscopy did not detect any defects, but the deep level transient spectroscopy showed response with activation energy of 0.33 eV and capture cross-section σn=(1-10)·10-19 cm2 and defect concentration (NT) is in the order of 1013 cm-3. This defect level is a trap for electron with position of 0.33 eV below the conduction band in region near the BP/Si interface.

Tendencies in ABO3 Perovskite and SrF2, BaF2 and CaF2 Bulk and Surface F-Center Ab Initio Computations at High Symmetry Cubic Structure

We computed the atomic shift sizes of the closest adjacent atoms adjoining the (001) surface F-center at ABO3 perovskites. They are significantly larger than the atomic shift sizes of the closest adjacent atoms adjoining the bulk F-center. In the ABO3 perovskite matrixes, the electron charge is significantly stronger confined in the interior of the bulk oxygen vacancy than in the interior of the (001) surface oxygen vacancy. The formation energy of the oxygen vacancy on the (001) surface is smaller than in the bulk. This microscopic energy distinction stimulates the oxygen vacancy segregation from the perovskite bulk to their (001) surfaces. The (001) surface F-center created defect level is nearer to the (001) surface conduction band (CB) bottom as the bulk F-center created defect level. On the contrary, the SrF2, BaF2 and CaF2 bulk and surface F-center charge is almost perfectly confined to the interior of the fluorine vacancy. The shift sizes of atoms adjoining the bulk and surface F-centers in SrF2, CaF2 and BaF2 matrixes are microscopic as compared to the case of ABO3 perovskites.

First-Principles Study of Carrier-Mediated and Vacancy-Induced Ferromagnetism in Molybdenum Disulfide Monolayer

We have investigated the magnetic properties of semiconducting molybdenum disulfide (MoS2) monolayer (ML) using the plane wave self-consistent field (PWscf) method within the framework of density functional theory (DFT). The pristine semiconducting bulk MoS2 is nonmagnetic (NM), due to the spin pairing of two electrons. We have indicated that the carrier-mediated ferromagnetism is available on the MoS2 ML as both the hole and electron carriers. The ordinary neutral S (VS0) vacancy creates the localized vacancy defect level and this level does not create the ferromagnetic (FM) state due to the spin pairing of two electrons by three Mo dangling bonds. While we have shown that the FM state is possible to create the FM state, due to the additional hole and electron carriers on the valency band and localized vacancy defect level by positively and negatively charged S (VS1+ and VS1- ) and positively charged Mo (VMo1+) vacancies.

Electron Polarons in Lithium Niobate: Charge Localization, Lattice Deformation, and Optical Response

Lithium niobate (LiNbO3), a material frequently used in optical applications, hosts different kinds of polarons that significantly affect many of its physical properties. In this study, a variety of electron polarons, namely free, bound, and bipolarons, are analyzed using first-principles calculations. We perform a full structural optimization based on density-functional theory for selected intrinsic defects with special attention to the role of symmetry-breaking distortions that lower the total energy. The cations hosting the various polarons relax to a different degree, with a larger relaxation corresponding to a larger gap between the defect level and the conduction-band edge. The projected density of states reveals that the polaron states are formerly empty Nb 4d states lowered into the band gap. Optical absorption spectra are derived within the independent-particle approximation, corrected by the GW approximation that yields a wider band gap and by including excitonic effects within the Bethe–Salpeter equation. Comparing the calculated spectra with the density of states, we find that the defect peak observed in the optical absorption stems from transitions between the defect level and a continuum of empty Nb 4d states. Signatures of polarons are further analyzed in the reflectivity and other experimentally measurable optical coefficients.

Nickel and gold identification in p-type silicon through TDLS: a modeling study

In Silicon, impurities introduce recombination centers and degrade the minority carrier lifetime. It is therefore important to identify the nature of these impurities through their characteristics: the capture cross section σ and the defect level Et. For this purpose, a study of the bulk lifetime of minority carriers can be carried out. The temperature dependence of the lifetime based on the Shockley-Read-Hall (SRH) statistic and related to recombination through defects is studied. Nickel and gold in p-type Si have been selected for the SRH lifetime modeling. The objective of the analysis is to carry out a study to evaluate gold and nickel identification prior to temperature-dependent lifetime measurements using the microwave phase-shift (μW-PS) technique. The μW-PS is derived from the PCD technique and is sensitive to lower impurity concentrations. It has been shown that both gold and nickel can be unambiguously identified from the calculated TDLS curves.

Localized electronic vacancy level and its effect on the properties of doped manganites

Oxygen vacancies are common to most metal oxides and usually play a crucial role in determining the properties of the host material. In this work, we perform ab initio calculations to study the influence of vacancies in doped manganites $$\text {La}_{(1-\text {x})} \text {Sr}_{\text {x}} \text {MnO}_{3}$$ La ( 1 - x ) Sr x MnO 3 , varying both the vacancy concentration and the chemical composition within the ferromagnetic-metallic range ($$0.2\,<\,\text {x}\,<\,0.5$$ 0.2 < x < 0.5 ). We find that oxygen vacancies give rise to a localized electronic level and analyse the effects that the possible occupation of this defect state can have on the physical properties of the host. In particular, we observe a substantial reduction of the exchange energy that favors spin-flipped configurations (local antiferromagnetism), which correlate with the weakening of the double-exchange interaction, the deterioration of the metallicity, and the degradation of ferromagnetism in reduced samples. In agreement with previous studies, vacancies give rise to a lattice expansion when the defect level is unoccupied. However, our calculations suggest that under low Sr concentrations the defect level can be populated, which conversely results in a local reduction of the lattice parameter. Although the exact energy position of this defect level is sensitive to the details of the electronic interactions, we argue that it is not far from the Fermi energy for optimally doped manganites ($$\text {x}\,\sim \,1/3$$ x ∼ 1 / 3 ), and thus its occupation could be tuned by controlling the number of available electrons, either with chemical doping or gating. Our results could have important implications for engineering the electronic properties of thin films in oxide compounds.