G. G. Scapellato

Transient enhanced diffusion of B mediated by self-interstitials in preamorphized Ge

The dissolution of interstitial-type end-of-range (EOR) damage in preamorphized Ge is shown to induce a transient enhanced diffusion of an epitaxially grown boron delta at temperatures above 350 °C that saturates above 420 °C. The B diffusion events are quantitatively correlated with the measured positive strain associated with the EOR damage as a function of the annealing temperature with an energy barrier for the EOR damage dissolution of 2.1±0.3 eV. These results unambiguously demonstrate that B diffuses in Ge through a mechanism assisted by self-interstitials, and impose considering the interstitial implantation damage for the modeling of impurity diffusion in Ge.

High-level incorporation of antimony in germanium by laser annealing

In this work we investigate pulse laser annealing as an alternative approach to reach high-level incorporation of Sb in substitutional location in crystalline germanium. Laser irradiation is demonstrated to recover also those structural defects, like honeycomb structures, that form during high-fluence heavy-ion implantations in Ge and that cannot be eliminated by conventional thermal treatments. Indeed, concentrations of substitutional Sb higher than 1×1021 at./cm3 have been obtained, well above the solid solubility of Sb in Ge. The strain induced on the Ge host lattice is also investigated, evidencing that the obtained Sb doped Ge layer is pseudomorphic to the Ge substrate while positively strained by the substitutional Sb atoms present within the Ge matrix. The kinetics of this Sb-rich Ge alloy phase is finally investigated, showing that most of Sb goes out of lattice with increasing the annealing temperature up to 488 °C, leading to a decrease in the related lattice deformation. These results are very ...

Laser irradiation of ZnO:Al/Ag/ZnO:Al multilayers for electrical isolation in thin film photovoltaics

Laser irradiation of ZnO:Al/Ag/ZnO:Al transparent contacts is investigated for segmentation purposes. The quality of the irradiated areas has been experimentally evaluated by separation resistance measurements, and the results are complemented with a thermal model used for numerical simulations of the laser process. The presence of the Ag interlayer plays two key effects on the laser scribing process by increasing the maximum temperature reached in the structure and accelerating the cool down process. These evidences can promote the use of ultra-thin ZnO:Al/Ag/ZnO:Al electrode in large-area products, such as for solar modules.

Light absorption and conversion in solar cell based on Si:O alloy

Thin film Si:O alloys have been grown by plasma enhanced chemical vapor deposition, as intrinsic or highly doped (1 to 5 at. % of B or P dopant) layers. UV-visible/near-infrared spectroscopy revealed a great dependence of the absorption coefficient and of the optical gap (Eg) on the dopant type and concentration, as Eg decreases from 2.1 to 1.9 eV, for the intrinsic or highly p-doped sample, respectively. Thermal annealing up to 400 °C induces a huge H out-diffusion which causes a dramatic absorption increase and a reduction of Eg, down to less than 1.8 eV. A prototypal solar cell has been fabricated using a 400 nm thick, p-i-n structure made of Si:O alloy embedded within flat transparent conductive oxides. Preliminary electrical analyses show a photovoltaic (PV) effect with an open circuit voltage of 0.75 V and a spectral conversion efficiency blue-shifted in comparison to a-Si:H based cell, as expected since the higher Eg in Si:O alloy. These data are presented and discussed, suggesting Si:O alloy as pr...

Enhanced light scattering in Si nanostructures produced by pulsed laser irradiation

An innovative method for Si nanostructures (NS) fabrication is proposed, through nanosecond laser irradiation (λ = 532 nm) of thin Si film (120 nm) on quartz. Varying the laser energy fluences (425–1130 mJ/cm2) distinct morphologies of Si NS appear, going from interconnected structures to isolated clusters. Film breaking occurs through a laser-induced dewetting process. Raman scattering is enhanced in all the obtained Si NS, with the largest enhancement in interconnected Si structures, pointing out an increased trapping of light due to multiple scattering. The reported method is fast, scalable and cheap, and can be applied for light management in photovoltaics.