Transient Electrical and Optical Characteristics of Electron and Proton Irradiated SiGe Detectors

The particle detector degradation mainly appears through decrease of carrier recombination lifetime and manifestation of carrier trapping effects related to introduction of carrier capture and emission centers. In this work, the carrier trap spectroscopy in Si1−xGex structures, containing either 1 or 5% of Ge, has been performed by combining the microwave probed photoconductivity, pulsed barrier capacitance transients and spectra of steady-state photo-ionization. These characteristics were examined in pristine, 5.5 MeV electron and 1.6 MeV proton irradiated Si and SiGe diodes with n+p structure.

Impact of strain relaxation on performance of α-formamidinium lead iodide perovskite solar cells

High-efficiency lead halide perovskite solar cells (PSCs) have been fabricated with α-phase formamidinium lead iodide (FAPbI3) stabilized with multiple cations. The alloyed cations greatly affect the bandgap, carrier dynamics, and stability, as well as lattice strain that creates unwanted carrier trap sites. We substituted cesium (Cs) and methylenediammonium (MDA) cations in FA sites of FAPbI3 and found that 0.03 mol fraction of both MDA and Cs cations lowered lattice strain, which increased carrier lifetime and reduced Urbach energy and defect concentration. The best-performing PSC exhibited power conversion efficiency >25% under 100 milliwatt per square centimeter AM 1.5G illumination (24.4% certified efficiency). Unencapsulated devices maintained >80% of their initial efficiency after 1300 hours in the dark at 85°C.

Current-Mode Deep Level Spectroscopy of Vanadium-Doped HPSI 4H-SiC

SiC has currently attracted the interest of the scientific community for qubit applications. Despite the importance given to the properties of color centers in high-purity semi-insulating SiC, little is known on the electronic properties of defects in this material. In our study, we investigated the presence of electrically active levels in vanadium-doped substrates. Current mode deep level transient spectroscopy, carried out in the dark and under illumination, together with 1-D simulations showed the presence of two electrically active levels, one associated to a majority carrier trap and the other one to a minority carrier trap. The nature of the detected defects has been discussed in the light of the characterization performed on low-energy electron irradiated substrates and previous results found in the literature.

Coupling Effect of Molecular Chain Displacement and Carrier Trap Characteristics on DC Breakdown of HDPE/LDPE Blend Insulation

This work focuses on the coupling effect of molecular chain displacement and trap characteristics on direct current (DC) breakdown properties of high density/low density polyethylene (HDPE/LDPE) blend insulation. Frequency domain spectroscopy (FDS) and isothermal discharge current (IDC) are used to characterize the dielectric relaxation and trap characteristics of HDPE/LDPE blends. A DC breakdown model is proposed to reveal the mechanisms of the molecular chain displacement and carrier trap on the DC breakdown strength. The dielectric relaxation α and δ present segmental motions and thermal ion polarization behaviours of HDPE/LDPE blends, respectively. α dielectric relaxation strength (Δεα) increases as the amount of HDPE increases from 0 to 5 wt%, and then declines with a further increase of HDPE content to 20 wt%. According to the velocity equation, the increase of Δεα will increase the molecular chain displacement, resulting in a larger free volume, which will provide electrons with larger free path λ to form hot electrons. A positive correlation exists between the activation energy of the dielectric relaxation process δ and trap density, and the increase of δ dielectric relaxation strength (Δεδ) will adversely affect the breakdown strength of the specimen. HDPE/LDPE blends with 15 wt% HDPE content have lower Δεα and lowest Δεδ, which decreases the mean free path λ of molecular chain and thermal ion polarization. At the same time, it has the highest deep trap density, thus increasing the probability of hot electrons being captured and improving the DC breakdown strength. It is concluded the breakdown of the dielectric is synergistically affected by the molecular chain displacement and carrier trap.

Емкостная спектроскопия гетероэпитакиальных AlGaAs/GaAs p-i-n-структур

Temperature dependences of capacitance-voltage (C−V) characteristics and deep-level spectra of the graded highvoltage AlxGa1−xAs p0 −i−n0 junction grown by liquid-phase epitaxy via autodoping with background impurities were investigated. The changes of the C−V characteristics at varied measurement temperature and optical illumination demonstrated that the p0-, i-,n0-type layers in the AlxGa1−xAs under study contain bistable DX centers. In spectra of deep-level transient spectroscopy (DLTS), measured at various bias voltages Vr and filling pulses Vf , a positive DLTS peak is observed for the n 0 -type layer with thermal activation energy Et = 280 meV and electron-capture cross-section σn = 3.17 · 10−14 cm2, which is unusual for a majority-carrier trap. This peak is related to the negatively charged state of the Se/Te donor impurity, which is a bistable DX center with negative correlation energy U.

Minority Carrier Trap in n-Type 4H–SiC Schottky Barrier Diodes

We present preliminary results on minority carrier traps in as-grown n-type 4H–SiC Schottky barrier diodes. The minority carrier traps are crucial for charge trapping and recombination processes. In this study, minority carrier traps were investigated by means of minority carrier transient spectroscopy (MCTS) and high-resolution Laplace-MCTS measurements. A single minority carrier trap with its energy level position at Ev + 0.28 eV was detected and assigned to boron-related defects.

Insight into sulfur vacancy-induced insulator to metal transition of Li2S

Sulfur vacancy-induced charge carrier trap is quite important for improving the insulating characteristic of Li2S. In this work, we apply the first-principle calculations to investigate the influence of sulfur intrinsic vacancy and sulfur vacancy concentration on the structure and conductivity of Li2S. Sulfur intrinsic vacancy is dynamically stable. Importantly, sulfur vacancy reduces the band gap of Li2S. The calculated band gap of sulfur intrinsic vacancy is 0.700[Formula: see text]eV. We suggest that the removed sulfur atom leads to Li-2[Formula: see text] state shift from conduction band to Fermi level and improves the charge overlap between the top of valence band (VB) and the bottom of conduction band (CB). The strong charge interaction of Li pairing atoms forms the Li–Li metallic bond. Finally, we predict that sulfur vacancy gives rise to the insulator to metal transition of Li2S. Our works open up a new possibility for improving the conductivity of Li2S.

Spin-polarized charge trapping cell based on a topological insulator quantum dot

We demonstrate theoretically that a topological insulator quantum dot can be formed via double topological insulator constrictions (TICs), and can be used as a charge and/or spin carrier trap memory element.