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Carrier Lifetime in Liquid-phase Crystallized Silicon on Glass
Liquid-phase crystallized silicon on glass (LPCSG) presents a promising material to fabricate high quality silicon thin films, e.g. for solar cells and modules. Barrier layers and a doped amorphous silicon layer are deposited on the glass substrate followed by crystallization with a line focus laser beam. In this paper we introduce injection level dependent lifetime measurements generated by the quasi steady-state photoconductance decay method (QSSPC) to characterize LPCSG absorbers. This contactless method allows a determination of the LPCSG absorber quality already at an early stage of solar cell fabrication, and provides a monitoring of the absorber quality during the solar cell fabrication steps. We found minority carrier lifetimes higher than 200ns in our layers (e.g. n-type absorber with ND=2x1015cm-3) indicating a surface recombination velocity SBL<3000cm/s at the barrier layer/Si interface.
Magnetically induced anisotropy of flux penetration into strong-pinning superconductor/ferromagnet bilayers
We studied the impact of soft ferromagnetic permalloy (Py) on the shielding currents in a strong-pinning superconductor - YBa2Cu3O7-δ with Ba2Y(Nb/Ta)O6 nano-precipitates - by means of scanning transmission x-ray microscopy. Typically and in particular when in the thin film limit, superconductor/ferromagnet (SC/FM) bilayers exhibit isotropic properties of the flux line ensemble at all temperatures. However, in elements with small aspect ratio a significant anisotropy in flux penetration is observed. We explain this effect by local in-plane fields arising from anisotropic magnetic stray fields originated by the ferromagnet. This leads to direction-dependent motion of magnetic vortices inside the SC/FM bilayer. Our results demonstrate that small variations of the magnetic properties can have huge impact on the superconductor.
Growth and applications of GeSn-related group-IV semiconductor materials
We review the technology of Ge1−xSnx-related group-IV semiconductor materials for developing Si-based nanoelectronics. Ge1−xSnx-related materials provide novel engineering of the crystal growth, strain structure, and energy band alignment for realising various applications not only in electronics, but also in optoelectronics. We introduce our recent achievements in the crystal growth of Ge1−xSnx-related material thin films and the studies of the electronic properties of thin films, metals/Ge1−xSnx, and insulators/Ge1−xSnx interfaces. We also review recent studies related to the crystal growth, energy band engineering, and device applications of Ge1−xSnx-related materials, as well as the reported performances of electronic devices using Ge1−xSnx related materials.
Surface effects and challenges for application of piezoelectric langasite substrates in surface acoustic wave devices caused by high temperature annealing under high vacuum
Substrate materials that are high-temperature stable are essential for sensor devices which are applied at high temperatures. Although langasite is suggested as such a material, severe O and Ga diffusion into an O-affine deposited film was observed during annealing at high temperatures under vacuum conditions, leading to a damage of the metallization as well as a change of the properties of the substrate and finally to a failure of the device. Therefore, annealing of bare LGS (La 3 Ga 5 SiO 14 ) substrates at 800 ∘ C under high vacuum conditions is performed to analyze whether this pretreatment improves the suitability and stability of this material for high temperature applications in vacuum. To reveal the influence of the pretreatment on the subsequently deposited metallization, RuAl thin films are used as they are known to oxidize on LGS at high temperatures. A local study of the pretreated and metallized substrates using transmission electron microscopy reveals strong modification of the substrate surface. Micro cracks are visible. The composition of the substrate is strongly altered at those regions. Severe challenges for the application of LGS substrates under high-temperature vacuum conditions arise from these substrate damages, revealing that the pretreatment does not improve the applicability.
Universal scaling behavior of the upper critical field in strained FeSe0.7Te0.3 thin films
Revealing the universal behaviors of iron-based superconductors (FBS) is important to elucidate the microscopic theory of superconductivity. In this work, we investigate the effect of in-plane strain on the slope of the upper critical field H c2 at the superconducting transition temperature T c (i.e. -dH c2/dT) for FeSe0.7Te0.3 thin films. The in-plane strain tunes T c in a broad range, while the composition and disorder are almost unchanged. We show that -dH c2/dT scales linearly with T c, indicating that FeSe0.7Te0.3 follows the same universal behavior as observed for pnictide FBS. The observed behavior is consistent with a multiband superconductivity paired by interband interaction such as sign change s ± superconductivity.
Laser Patterning of CIGS thin Films with 1550 nm Nanosecond Laser Pulses
The results of laser scribing experiments of CIGS thin films deposited on Mo-coated stainless steel sheets, using laser pulses with a wavelength of 1550 nm and a pulse duration of 6 ns, are presented in this study. It is shown that a removal of the CIGS from the Mo film is possible without edge melting of the CIGS or damaging of the Mo. The critical parameter for inducing the delamination lift-off process of the CIGS from the Mo was identified to be the scribing speed of the laser. In dependence on the laser parameters two different material removal processes were found. For a low pulse overlap the laser pulse penetrates the CIGS film and is absorbed in the interface between the CIGS and the Mo causing a lift-off process of the CIGS from the Mo back contact. For a high pulse overlap an ablation process starting from the top side of the CIGS film was found. The composition and morphology of the sample material after the laser patterning were analysed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and micro-Raman spectroscopy.
Micromagnetic investigation of domain and domain wall evolution through the spin-reorientation transition of an epitaxial NdCo5 film
The domain pattern and the domain wall microstructure throughout the spin-reorientation transition of an epitaxial NdCo5 thin film are investigated by micromagnetic simulations. The temperature-dependent anisotropy constants K1 and K2, which define the anisotropy energy term in the model, are chosen to reflect the easy axis—easy cone—easy plane spin-reorientation transition observed in epitaxial NdCo5 thin films. Starting at the high-temperature easy c-axis regime, the anisotropy constants are changed systematically corresponding to a lowering of the temperature of the system. The character of the domain walls and their profiles are analysed. The calculated domain configurations are compared to the experimentally observed temperature-dependent domain structure of an in-plane textured NdCo5 thin film.