High-efficiency multijunction or tandem solar cells based on group III–V semiconductor alloys are applied in a rapidly expanding range of space and terrestrial programs. Resistance to high-energy radiation damage is an essential feature of such cells as they power most satellites, including those used for communications, defense, and scientific research. Recently we have shown that the energy gap of In1−xGaxN alloys potentially can be continuously varied from 0.7 to 3.4 eV, providing a full-solar-spectrum material system for multijunction solar cells. We find that the optical and electronic properties of these alloys exhibit a much higher resistance to high-energy (2 MeV) proton irradiation than the standard currently used photovoltaic materials such as GaAs and GaInP, and therefore offer great potential for radiation-hard high-efficiency solar cells for space applications. The observed insensitivity of the semiconductor characteristics to the radiation damage is explained by the location of the band edge...

Superior radiation resistance of In1-xGaxN alloys: Full-solar-spectrum photovoltaic material system

The use of nonionizing energy loss (NIEL) in predicting the effect of gamma, electron, and proton irradiations on Si, GaAs, and InP devices is discussed. The NIEL for electrons and protons has been calculated from the displacement threshold to 200 MeV. Convoluting the electron NIEL with the slowed down Compton secondary electron spectrum gives an effective NIEL for CO/sup 60/ gammas, enabling gamma-induced displacement damage to be correlated with particle results. The fluences of 1 MeV electrons equivalent to irradiation with 1 Mrad(Si) for Si, GaAs, and InP are given. Analytic proton NIEL calculations and results derived from the Monte Carlo TRIM agree exactly, as long as straggling is not significant. The NIEL calculations are compared with experimental proton and electron damage coefficients using solar cells as examples. A linear relationship is found between the NIEL and proton damage coefficients for Si, GaAs, and InP devices. For electrons, there appears to be a linear dependence for n-Si and n-GaAs, but for p-Si there is a quadratic relationship which decreases the damage coefficient at 1 MeV by a factor of approximately 10 below the value for n-Si. >

Damage correlations in semiconductors exposed to gamma, electron and proton radiations

The concept of nonionizing energy loss (NIEL) has been found useful for characterizing displacement damage effects in materials and devices. Published tabulations, however, are limited with respect to target materials, particle types and energies. In this paper we show how the NIEL database can be significantly expanded to include heavy ions in the coulombic limit by using the Monte Carlo code SRIM. The methodology used to extract NIEL from SRIM is described. This greatly adds to the number of materials and incident particles for which the NIEL concept can be applied. To show that values so derived are consistent with previous calculations, we compare alpha particle NIEL for GaAs derived from SRIM with a direct analytical calculation. The SRIM code is limited in that only coulombic interactions are considered. General rules of thumb are also described which permit prediction of NIEL for any target material over a large energy range. Tabulated values of NIEL for alpha particles incident on Si, GaAs and InP are presented.

Nonionizing energy loss (NIEL) for heavy ions

THE critical current density across individual grain boundaries in thin films of the high-Tc superconductor YBa2Cu3O7–δ (YBCO) has been found1–4 to be inversely proportional to lattice misorientation for tilts up to ∼10°. Reports of impurity segregation5,6 at grain boundaries, and variations in the chemical stoichiometry7,8, have led to the view that deviations from the ideal composition are responsible for the depressed superconducting order parameter at the boundary. Here we present images of YBCO grain boundaries obtained by a scanning transmission electron microscope in Z-contrast mode9,10, which show that chemical segregation does not necessarily occur at these boundaries. A simple model of the strain associated with the grain-boundary dislocations provides a reasonable physical explanation of the suppressed superconductivity. The surprisingly large effect of strain implied by our model has implications beyond critical currents, for the physics and applications of any thin-film YBCO structures involving strained epitaxial layers.

Structural origin of reduced critical currents at YBa2Cu3O7–δ grain boundaries

Columnar defects introduced by irradiation with very energetic heavy ions are the most effective pinning centres for flux lines in high-temperature superconductors. This correlated disorder generates large increases in the critical current densities and expansion of the irreversible regime in and the various Bi- and Tl-based compounds. In single crystals and thin films, the pinning enhancement is strongly angular-dependent, and maximizes when the applied magnetic field is parallel to the amorphous latent tracks. In contrast, in the much more anisotropic Bi- and Tl- based materials this unidirectional anisotropy is very small due to the quasi two-dimensional character of the vortices. Some of the extensive experimental studies on this topic are reviewed. Measurements of the temperature, field and defect density dependence of the persistent currents and their time relaxation in YBCO are presented. The analysis of these results based on recent theoretical models permits the identification of various pinning and creep regimes. Studies in other compounds, including technologically relevant Bi-based tapes, are summarized. The influence of the angular dispersion (splay) of the tracks on vortex pinning and creep is discussed.

https://iopscience.iop.org/article/10.1088/0953-2048/10/7A/003/pdf

Vortex pinning and creep in high-temperature superconductors with columnar defects

The particle‐induced depression of the superconducting critical temperature Tc of YBa2Cu3O7−δ is shown to be directly proportional, over seven orders of magnitude, to the nonionizing energy deposited in the lattice by primary knock‐on atoms displaced by incident electrons, protons, and heavy ions. It is concluded that ΔTc is proportional only to the average number of defects produced and can therefore be predicted for any particle, energy, and fluence from a calculation of the nonionizing energy loss.

Effect of particle-induced displacements on the critical temperature of YBa2Cu3O7−δ

The particle-induced depression of the superconducting critical temperature, T/sub c/, of YBa/sub 2/Cu/sub 3/O/sub 7- delta / is shown to be directly proportional to the nonionizing energy loss (NIEL) of primary knock-on atoms (PKAs) displaced by incident electrons, protons, and heavy ions, which cover a NIEL range of over seven orders of magnitude. Calculations of the NIEL for electrons and protons are given for YBa/sub 2/Cu/sub 3/O/sub 7/ over the range 1-1000 MeV. The partition of NIEL among the elements as a function of incident electron energy is discussed. For a given particle fluence Phi , it is concluded that dT/sub c//d Phi is proportional to the average number of defects produced, is not affected by the formation of defects in cascades, and is independent of the PKA spectrum. This means that the particle-induced depression of T/sub c/ can be predicted for any particle type, for any energy, and for any fluence. >

Electron and proton radiation effects in the high temperature superconductor YBa/sub 2/Cu/sub 3/O/sub 7- delta /

We have investigated the effects of low fluence (<1014 cm−2 ) 63 MeV H+ and 65 MeV He2+ irradiation of prototype thin films of YBa2Cu3O7−δ produced by a plasma‐arc spray technique. The observed changes in the resistance versus temperature behavior are much more dramatic than that observed for films produced by other techniques and resembles qualitatively a bond percolation threshold. The radiation sensitivity of these plasma‐arc spray films is concluded to be due to poor intergranular characteristics. This information is being used to modify the processing steps to improve the properties of films produced by this technique.

Catastrophic loss of superconductivity in ion‐irradiated films of YBa2Cu3O7−δ

The effects of proton irradiation on the performance of films and microwave devices made from the high temperature superconductors YBa/sub 2/Cu/sub 3/O/sub 7- delta / and Tl/sub 2/Ca/sub 2/BaCu/sub 2/O/sub 8/ have been measured and can be explained in terms of radiation-induced changes in material parameters such as surface impedance, critical current and transition temperature. Changes in material parameters can in turn be linked to atomic displacement effects. >

E.A. Burke

Papers

Effect of particle-induced displacements on the critical temperature of YBa2Cu3O7−δ

Electron and proton radiation effects in the high temperature superconductor YBa/sub 2/Cu/sub 3/O/sub 7- delta /

Catastrophic loss of superconductivity in ion‐irradiated films of YBa2Cu3O7−δ

Radiation effects in high temperature superconducting films and devices for the NRL high temperature superconductivity space experiment