No abstract

In this work, results of controlled detachment of (111) silicon by stress induced spalling (SIS) process, which is based on a gluing on a metallic stressor layer by an epoxy adhesive on top of a silicon substrate, are presented. It is shown that silicon foils mainly (1 × 1) cm 2 with different thicknesses (~50-170 µm) can be successfully detached using different materials (steel, copper, aluminum, nickel and titanium) as stressor layers with thicknesses ~50-500 µm. Such detachment can be realized by dipping of a stressor/glue/silicon wafer based structure into liquid nitrogen. As a result, Si foils with different thicknesses from ~50 µm to ~170 µm can be detached. An analytical and numerical approaches based on principles of linear elastic fracture mechanics is developed and they are shown that such approaches can predict general trends and conditions for the detachment of silicon foils with desired thicknesses using a stressor layer. Raman spectroscopy analysis of the residual stresses in detached silicon foils shows, that tensile stresses (up to −36 MPa) as well as higher value compressive stresses (up to ~444 MPa) are present in such foils. Moreover, optical and scanning electron microscopy (SEM) measurements show that surface of the detached foils exhibits some periodic lines originated by stresses.

a‐Si:H thin films‐based solar cells offer the benefit of reducing material consumption and fabrication costs. However, such thin absorbing layer reduces the photovoltaic efficiency, due to their poor light absorption at red and near‐infrared wavelengths. Metal NPs such as silver (Ag) can exhibit strong localized surface plasmon (LSP) resonances at different wavelength ranges, allowing increasing the light absorption in the active layer. The goal of this study is to perform an optimal structure of Ag NPs allowing to optimize the light absorption within the a‐Si:H solar cells by means of scattering. Ag layers are deposited on two different SnO2 substrates (with different roughness). After annealing, quasi‐spherical shaped of Ag NPs with diameters ranging from 10 to 130 nm are obtained. UV‐visible spectroscopy displays one LSP resonance around 560 nm with the less rough substrate, while three LSP resonances around 560, 700, and 850 nm are observed with roughest substrate. These differences are mainly due to the size distribution of NPs and underline the strong influence of the surface roughness and the coupling effect on the NPs behavior. a‐Si:H thin film solar cells with Ag NPs are subsequently elaborated. Spectral response shows an improvement of about 14–15%.

In this work, we studied the potential use of low‐energy hydrogen implantation as a guide for the stress‐induced cleavage. Low‐energy, high fluence hydrogen implantation in silicon leads, in the right stiffening conditions, to the detachment of a thin layer, around a few hundreds nm thick, of monocrystalline silicon. We implanted monocrystalline silicon wafers with low‐energy hydrogen, and then glued them on a cheap metal layer. Upon cooling down, the stress induced by the stressor layers (hardened glue and metal) leads to the detachment of a thin silicon layer, which thickness is determined by the implantation energy. We were then able to clearly demonstrate that, as expected, hydrogen oversaturation layer is very efficient to guide the stress. Using such process, thin silicon layers of around 710 nm‐thick were successfully detached from low‐energy implanted silicon wafers. Such layers can be used for the growth of very good quality monocrystalline silicon of around 50 µm‐thick or less. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

In this paper, we report on implantation parameters allowing the delamination of large surface of ultra‐thin silicon substrates by using MeV hydrogen implantation. We particularly focus on the effects of both hydrogen fluence and implantation energy, on the size of the largest delaminated surface in one piece. We demonstrate that thin silicon substrates with thicknesses between 30 µm and 70 µm can be extracted from silicon commercial wafers. In this study, the used‐material, the implantation energy and the hydrogen fluence ranges are (100) Si, 1.5 MeV‐2.5 MeV, 1×1017cm–2‐2×1017cm–2, respectively. We find that, by increasing hydrogen fluence, the maximum achievable surface of delaminated substrates in one piece can be doubled. Indeed, by XTEM, we observed that fracture precursor defects are mostly oriented along {111} in the case of the lowest fluence, which are unfavorable for a good surface‐parallel crack propagation. For the highest fluence, precursors are oriented along {100} which are parallel to the substrate surface, therefore they allow propagation over longer distances of cracks parallel to the substrate surface. We also find that, despite of the raise of the proportion of precursors oriented along {111}, the total surface of delaminated substrates significantly increases with the implantation energy. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)