Diffuse X-Ray Scattering Study of Defects Created by keV Ion Implants in Si

Diffuse scattering is a general phenomenon associated with various nanoscale disorders omnipresent in crystalline solids. While it contains rich information on structural disorders, interpretation and analysis of diffuse scattering pose a great challenge because it usually contains contributions from multiple types of disorders and their respective contributions are difficult to separate. In order to extract useful information from diffuse scattering, concerted efforts in high-quality diffuse scattering intensity measurement, quantitative data analysis, theoretical interpretation, and computer simulations are required. In this theoretical work, the diffuse scattering intensity distribution associated with static and dynamic atomic position fluctuations is formulated to effectively combine with our concurrent experimental and computational works. In particular, the theoretical formulation is used to interpret diffuse scattering originated from phonon softening in precursor state of a shape-memory alloy, and, as examples of static atomic position fluctuations, diffuse scattering phenomena of modulated phases and nanotwin microstructures are also discussed.

Comparing the radiolytic oxidation of sulfur and chloride within ice on Europa and Mars

Diffuse scattering – the coherently scattered intensity that is not localised on the reciprocal lattice – contains a wealth of information about the local order (order on the nanoscale) in crystalline materials. Since molecules and atoms will respond most strongly to their local chemical environments, it is a valuable tool in understanding how structure leads to properties. However, at present its collection and analysis are relatively specialised. Monte Carlo (MC) computer simulation of a model structure has become a powerful and well-accepted technique for aiding the interpretation and analysis of diffuse scattering patterns. Its great strength is its flexibility – as long as an MC energy can be defined, a model can be developed and tested. At one extreme a very simplified model may be useful in demonstrating particular qualitative effects, while at the other a quantitative and very detailed description of disordered structures can be obtained. Examples discussed include new results concerning p-chloro-N-(p-chloro-benzylidene)aniline, a molecule showing various degrees of molecular flexibility.

Point defects were controllably introduced into 270 nm AlGaN Light-Emitting Diodes (LEDs) by 5 MeV electron and 1.1 MeV proton irradiations to examine the effect on electrical and luminescent characteristics. The 5 MeV electron irradiations had only a marginal effect on the charge distribution, current flow, and electroluminescence of LEDs for electron fluences up to 4.5 × 1016 e/cm2 that cause very strong degradation in green, blue, and near-UV LEDs. This lack of changes is attributed to the much higher charge densities in quantum-wells (QWs) and quantum barriers (QBs) of the 270 nm LEDs and to higher bond strength in high Al mole fraction AlGaN layers. By contrast, irradiation with 1.1 MeV protons with a fluence of 1016 p/cm2 leads to more than two orders of magnitude decrease in charge density in the QWs and QBs, a strong increase in the series resistance, and the emergence of deep electron traps near Ec-0.5 eV. The difference is explained by a much higher density of primary defects produced by protons. The observed effects are compared to changes in performance caused by aging after high driving current.

Defect size dependence of critical current density enhancement for irradiated YBa 2Cu 3O 7−δ

Because of their state of art technology, GaAs solar cells are generally preferred for spatial applications. Exposure to proton and electron irradiations, solar cells suffer significant degradation in their performance such as short circuit current and open circuit voltage. Adding a window layer helps in effectively reducing the surface recombination at the emitter surface of the solar cell without absorbing the useful light required for the device. It remains to study the physics of the window-emitter hetero-interface in order to understand how the window layer presence increases the minority carrier lifetime of the solar cell exposed to particles irradiation. In this work Numerical simulation has been used to study the AlxGa1- xAs window composition effect on the current-voltage characteristics of a GaAs solar cell under AM0 illumination and exposed to 1 MeV electron irradiation. To predict the effect of window layers on solar cells degradation, the current voltage characteristic are evaluated for different electron irradiation fluences. The findings are supported by experimental data. They lead us to get to know how the window layer improves resistance to electron irradiation through its own parameters.

The reduction in temperature-dependent hole concentration p(T) in Al-implanted p-type 6H-SiC by 1 MeV electron irradiation is investigated. By analysis of p(T), the density (NA), level position (EA) in the bandgap and nature of the acceptor are determined, and this acceptor is assigned to an Al acceptor. EA is independent of irradiation fluence (Φ), while NA is strongly dependent on Φ. We derived an analytical expression for the fluence dependence of NA and we estimated the removal coefficient (i.e., removal cross-section) of NA to be 6.4×10-18 cm2 for 1 MeV electron irradiation. The reduction in p(T) by electron irradiation is found to be mainly due to the decrease in NA, not to the increase in the density of deep-level defects in the bandgap, because the decrement in NA is much larger than the increment in the density of deep-level defects.

In this study, the degradation of photovoltaic properties of NiO/ZnO visible-light-transparent solar cells after 2 MeV electron irradiation is investigated to explore the possibility of space applications. No significant degradation is observed after 2 MeV electron irradiation at the fluence of 1 × 1017 cm−2. The electrical performance of NiO/ZnO solar cells exhibited a higher electron irradiation resistance than that of polycrystalline Si or Cu(In,Ga)Se2 solar cells. The high electron irradiation resistance of NiO/ZnO solar cells is thought to be due to large threshold displacement energies of NiO and ZnO, and also to the recovery from radiation-induced damage at room temperature. These results represent the first step toward the realization of the practical application of NiO/ZnO solar cells in space.

Electrical conductivity and current-voltage characteristics of alumina with or without neutron and electron irradiation

SummaryThe degradation characteristics of lattice‐matched (LM) GaInP/InGaAs/Ge solar cell under 1 MeV electron irradiation are numerically simulated using APSYS finite element analysis software and Essential Macleod Program. Main output parameters of solar cells are simulated based on the material energy band, minority carrier lifetime, and interface surface recombination velocity. The results show that the adverse effects of the displacement damages in solar cell materials induced by irradiation are the primary reasons for overall cell performance degradation. The minority carrier lifetime degraded mostly in InGaAs middle subcell after irradiation, and it became to the current‐limiting unit in the end‐of‐life condition. The simulation results of the current‐voltage curves and the external quantum efficiency spectra are well agreed with the irradiation experimental data under similar conditions. Furthermore, an approach to radiation hardening of LM GaInP/InGaAs/Ge solar cell by adjusting the base and emitter layer thickness in the InGaAs middle subcell is proposed based on this model.

Formation of nano-structure in melt-spun ternary Fe-Nd-B alloys was examined focusing on electron irradiation induced crystallization. In Fe 82.2 Nd 7.1 B 10.7 (Fe/Nd/B = 23/2/3), Fe 77 Nd 4.5 B 18.5 and Fe 71 Nd 9 B 20 alloys, melt-spun amorphous phase changed to a crystalline phase during electron irradiation and nano-structure was formed. The crystalline phase in melt-spun Fe 86 Nd 9 B 5 and Fe 82.4 Nd 11.8 Β 5.8 (Fe/Nd/B = 14/ 2/1) alloys was unstable under electron irradiation and electron irradiation induced amorphization occurred. With the further irradiation, crystallization from the amorphous phase was induced resulting in forming nano-crystalline structure. The onset total dose for the irradiation induced crystallization, namely, stability of the amorphous phase against electron irradiation depends strongly on the Fe-ratio, crystallization temperature, mismatch entropy and mixing enthalpy of the alloys.

GaAs solar cells hold the record for the highest single band-gap cell efficiency. Successful application of these cells in advanced space-borne systems demand characterization of cell properties like dark current under different ambient conditions and the stability of the cells against particle irradiation in space. In this paper, the results of the studies carried out on the effect of 8 MeV electron irradiation on the electrical properties of GaAs solar cells are presented. The I–V (current-voltage) characteristics of the cells under dark and AM1.5 illumination condition are studied and 8 MeV electron irradiation was carried out on the cells where they were exposed to graded doses of electrons from 1 to 100 kGy. The devices were also characterized using capacitance measurements at various frequencies before and after irradiation. The effect of electron irradiation on the solar cell parameters was studied. It is found that only small changes were observed in the GaAs solar cell parameters up to an electron dose of 100 kGy, exhibiting good tolerance for electrons of 8 MeV energy.

Origin of yellow luminescence in n-GaN induced by high-energy 7 MeV electron irradiation

In situ observation of solid-state amorphization in Nd 2Fe 14B alloy by electron irradiation

Radiation induced deuterium absorption for RB-SiC, HP-SiC, silicon and graphite loaded during electron irradiation