M. Levalois

Deep level transient spectroscopy of high‐energy heavy ion irradiation‐induced defects in n‐type germanium

Swift heavy ion irradiation‐induced defects have been studied in n‐type germanium at room temperature using deep level transient spectroscopy. Several electron traps have been observed after irradiation. The corresponding energies have been determined to be at Ec−0.22, Ec−0.275, Ec−0.29, Ec−0.32, and Ec−0.465 eV. The isochronal annealing behavior of these traps has been studied in detail between room temperature and 200 °C. Comparison of our results with previously published ones allowed an identification of these defects with complexes like divacancies or associations of vacancies with impurities.

A high-resistivity phase induced by swift heavy-ion irradiation of Bi: a probe for thermal spike damage?

Pure bismuth samples were irradiated at 20 K with swift heavy ions from 18O to 238U in the GeV range. The rate of the induced damage was deduced from in situ electrical resistance measurements. Above a threshold in the electronic stopping power Se equal to 24 keV nm-1, the damage is due to electronic slowing down. Above 30 keV nm-1, the electronic slowing down is efficient enough to induce latent tracks attributed to the appearance of a high-resistivity phase. The induced latent tracks radii can be up to 21.9 nm for Se=51 keV nm-1 which is the largest value reported so far for non-radiolytic materials. The evolution with Se of the latent tracks radii is calculated on the basis of the thermal spike model, assuming a realistic value for the electron-phonon coupling constant. A rather good agreement is obtained which supports the idea that the thermal spike could be operative in the observed radiation damage.

Optimized conditions for an enhanced coupling rate between Er ions and Si nanoclusters for an improved 1.54-μm emission

The present article deals with the optimized processing conditions leading to the highest density of Si nanoclusters which play the role of sensitizing centers for the nearby Er ions within a silica matrix. The layers were obtained by reactive magnetron sputtering under a plasma of Ar mixed to different rates of hydrogen, and were subsequently annealed at various temperatures. The increase of the dilution degree of the Ar plasma with hydrogen was found to multiply the nucleation sites whose density foreshadows that of the Si nanoclusters formed upon annealing. Both hydrogen content and annealing temperature govern the growth of the clusters. The maximum density of efficient sensitizing centers was obtained for hydrogen rate in the plasma of 50% and annealing at 900 °C. This has directly led to the enhancement of the coupling rate between the Si nanoclusters and the Er ions, as reflected by the ten times increase of the proportion of optically active ions, compared to that for standard conditions. In paral...

Induced damage by high energy heavy ion irradiation at the GANIL accelerator in semiconductor materials

Abstract The advantages of using a high energy (several GeV) heavy ion accelerator for irradiation are first recalled: the ranges of ions in materials are significant; an a priori relative evaluation of the damage creation rates from elastic collisions is possible; last, the ratio of the electronic stopping power to the nuclear stopping power is very large. The experimental methods used are in situ resistance and Hall mobility measurements. The irradiated samples are also analyzed in the laboratory by means of different methods (DLTS, photoluminescence, electron microscopy). The resistance has the same behaviour in silicon and gallium arsenide. It increases continuously during the irradiation. On the other hand, in n-type germanium, the resistance first increases, passes through a maximum, and decreases afterwards. A type-conversion takes place in the material. Moreover, the comparison of damage creation rates from one irradiation to another, in germanium and gallium arsenide, seems to show that the electron excitation produces a relative decrease of the damage creation rate. This effect is not visible in silicon.

Room-temperature 1.54 μm photoluminescence from Er-doped Si-rich silica layers obtained by reactive magnetron sputtering

Er-doped Si-rich silica layers were obtained by reactive magnetron sputtering and both structural and room-temperature photoluminescence properties were investigated. The controlled introduction of hydrogen in the plasma was found to play a critical role in the microstructure and distribution of the Si nanograins formed after annealing. Concomitant density increase and size decrease of these nanograins mostly amorphous were noticed upon increasing the hydrogen partial pressure in the plasma. This was accompanied by a systematic enhancement of the Er emission indicating that both crystallized and amorphous silicon nanoparticles are similarly efficient sensitizers for Er emission. The lifetime of the latter was found as high as 5–6 ms.

Latent track formation in germanium irradiated with 20, 30 and 40 MeV fullerenes in the electronic regime

Abstract Conventional transmission electron microscopy (TEM) and high resolution electron microscopy (HREM) have been performed on irradiated germanium with a few tens of MeV C 60 incident clusters (fullerenes). Normal and inclined incidences of the beam have been investigated. As observed in the case of silicon, microscopy observations after irradiation with 20, 30 and 40 MeV beams show clearly the presence of cylindrical amorphous latent tracks of 6, 10.6 and 12.5 nm in diameter, respectively. Other microstructural considerations are reported. The difference in diameter has been interpreted in terms of high electronic energy deposited by the three different energetic fullerene beams. Furthermore, during HREM observation, a recrystallisation process of the amorphous region of the tracks has been observed and analysed.

Observations by X-ray diffraction of structural changes in mica irradiated by swift heavy ions

Abstract The descriptions of high-energy ion irradiation damage in mica by small-angle X-ray/neutron scattering and electron microscopy are used to support some models of track formation in dielectric solids. More recently heavy ion tracks in mica could be observed by atomic force microscopy and the dependence of the track radius on the particle energy loss is in contradiction with previous results. This discrepancy as well as the structural modifications (i.e. amorphization, dilatation, distortions) of ion-irradiated mica are discussed using the technique of wide-angle X-ray diffraction.

Latent track formation in GaAs irradiated with 20, 30, and 40 MeV fullerenes

Microstructural observations of gallium arsenide single crystals irradiated with a few tens of MeV C60 incident clusters (fullerenes) were performed. Normal and grazing incidences were investigated. Similar to in the case of silicon and germanium, cylindrical amorphous tracks whose diameters vary as a function of the projectile energy were found. However, for a given energy of the clusters, the track diameters are slightly different from one material to another. Also depending on the fullerene, energy is the length of the amorphous cylinder that formed along the projectile’s path. The recrystallization process under an electron beam during transmission electron microscopy observation was analyzed and a higher growth rate for gallium arsenide compared to that of germanium was seen.

High energy ion irradiation of germanium

Abstract Irradiations of n- and p-doped germanium samples have been performed at room temperature at GANIL (Caen) using Ar (1415 MeV), Xe (5510 MeV and 751 MeV), Ca (272 MeV), Zn (691 MeV), O (195 MeV) and Kr (427 MeV) ions. The sample resistance and Hall mobility were measured in situ as a function of the ion fluence. In p-Ge samples the conductivity and the majority carrier density steadily increase up to the maximum fluences used (about 1012 cm−2). The conductivity σ of n-Ge samples first decreases, reaches a minimum at a fluence depending on the initial doping concentration and then increases. At the minimum value of σ, Hall measurements show a transition from n- to p-type conductivity. These results show that acceptor energy levels are created by irradiation induced defects. At low electronic stopping power values, the creation rate of acceptor levels is approximately a linear function of the calculated number of displacements per atom. This linear dependence becomes invalid at high electronic stopping power values. This last result could be explained by assuming a partial annealing of the defects for the largest electronic stopping power.

Sensitivity of metallic materials under irradiation with swift heavy ions

Abstract We report on experimental results on metallic materials (Ag,Sn) after irradiation with swift heavy ions. These results, in addition to previous ones, show that the behaviour of that kind of materials could be well described in the framework of the thermal spike model. We find a good correlation between theoretical results and experimental ones provided that the only free parameter of the model should be known: the number z of electrons involved in the thermal spike mechanism via the electron phonon coupling constant. It is shown that the values of z must lie in the range of 1 and 2 electrons per atom. A simple criterion is deduced and used to know whether a given material could be sensitive or not to the electronic slowing down of swift heavy ions.