Search

Growing high-quality Si films at high rates with thicknesses ranging from the few nm- to µm-range while keeping the material consumption at a minimum is important for a wide range of Si-based technologies, spanning from batteries to sensors and solar cells. In this work, we elucidate the effects of electron beam deposition (e-beam) conditions on the growth of ~4 µm thick Si layers on bare and thermally oxidized (001)-oriented Si substrates. All depositions are performed from a stabilized and refillable melt of broken B-doped wafers and recollected using Si-shields during deposition for recycling. We find that increasing the deposition rate from 0.3 to 23 nm/s at a substrate temperature of 1000 °C reduces the roughness, void fraction, and residual stress of epitaxial Si-on-Si layers. For Si-on- S i O 2 , all films are polycrystalline under the same deposition conditions as for Si-on-Si, with a reduction in void fraction and increase in roughness at higher deposition rates. The residual stress for Si-on- S i O 2 is comparable across all deposition rates >1 nm/s. Furthermore, we measure lower resistivities in the films than in the feedstock for Si-on-Si and higher than the feedstock for Si-on- S i O 2 . While the films become microstructurally denser and less defective at higher deposition rates, the resistivity increases for each next deposition step in the case of multi-step depositions from the same feedstock. Time-of-flight scanning secondary mass spectroscopy measurements show that the films have a significantly higher B-concentration than the feedstock, suggesting B-gettering to the melted region and transferring to the Si film upon the e-beam deposition process. This work demonstrates how electron beam evaporation can be used to recollect and recycle waste Si pieces, bringing important insights into how the deposition parameters influence the quality of the deposited polycrystalline as well as epitaxial thin-to-thick films. [ABSTRACT FROM AUTHOR]

This paper describes the high-rate (~1.5 μm/min) growth of Si films on Si supporting substrates with (100) crystallographic orientation at 600 °C, 800 °C, and 1000 °C in a vacuum environment of ~1 × 10−5 mbar using electron beam (e-beam) evaporation. The microstructure, crystallinity, and conductivity of such films were investigated. It was established that fully crystalline (Raman spectroscopy, EBSD) and stress-free epi-Si layers with a thickness of approximately 50 µm can be fabricated at 1000 °C, while at 600 °C and 800 °C, some poly-Si inclusions were observed using Raman spectroscopy. Hall effect measurements showed that epi-Si layers deposited at 1000 °C had resistivity, carrier concentration, and mobility comparable to those obtained for c-Si wafers fabricated through ingot growth and wafering using the same solar grade Si feedstock used for the e-beam depositions. The dislocation densities were determined to be ∼2 × 107 cm−2 and ∼5 × 106 cm−2 at 800 and 1000 °C, respectively, using Secco etch. The results highlight the potential of e-beam evaporation as a promising and cost-effective alternative to conventional CVD for the growth of epi-Si layers and, potentially, epi-Si wafers. Some of the remaining technical challenges of this deposition technology are briefly indicated and discussed. [ABSTRACT FROM AUTHOR]

In this study, laser-treated polycrystalline Si (pc-Si) wafers, fabricated by wire sawing of hot-pressed ingots sintered from Si powder, have been investigated. As-cut wafers and those with high-quality thin Si layers deposited on top of them by e-beam have been subjected to laser irradiation to clarify typical trends of structural modifications caused by laser treatments. Moreover, possibility to use laser-treated Si powder-based substrates for fabrication of advanced Si structures has been analysed. It is established that (i) Si powder-based wafers with thicknesses ~180 μm can be fully (from the front to back side) or partly (subsurface region) remelted by a diode laser and grain sizes in laser-treated regions can be increased; (ii) a high-quality top layer can be fabricated by crystallization of an additional a-Si layer deposited by e-beam evaporation on top of the pc-Si; and (iii) silicon nanowires can be formed by metal-assisted wet chemical etching (MAWCE) of polished Si powder-based wafers and as-cut wafers irradiated with medium laser power, while a surface texturing on the as-cut pc-Si wafers occur, and no nanowires can form in the region subject to a liquid phase crystallization (LPC) caused by high-power laser treatments.

Thin films of homogeneous mixture of amorphous silicon and aluminum were produced with magnetron sputtering using 2-phase Al–Si targets. The films exhibited variable compositions, with and without the presence of hydrogen, aSi1−xAlx and aSi1−xAlxHy. The structure and optical properties of the films were investigated using transmission electron microscopy, X-ray photoelectron spectroscopy, UV-VisNIR spectrometry, ellipsometry, and atomistic modeling. We studied the effect of alloying aSi with Al (within the range 0–25 at. %) on the optical band gap, refractive index, transmission, and absorption. Alloying aSi with Al resulted in a non-transparent film with a low band gap (1 eV. Variations of the Al and hydrogen content allowed for tuning of the optoelectronic properties. The films are stable up to a temperature of 300 °C. At this temperature, we observed Al induced crystallization of the amorphous silicon and the presence of large Al particles in a crystalline Si matrix.

High entropy alloy (HEA) films of CrFeCoNiCu were deposited by sputtering. Their structure was characterized and their electric transport properties were studied by temperature-dependent Hall and Seebeck measurements. The HEA films show a solid solution with an fcc structure. The residual electrical resistivity of the films is around 130 μΩ cm, which is higher than the Mott limit for a metal while the temperature dependence of the resistivity above 30 K is metal-like but with a small temperature coefficient of resistivity (2 ppm/K). The dominant scattering mechanism of charge carriers is alloy scattering due to chemical disorder in the HEA. The Hall coefficient is positive while the Seebeck coefficient is negative. This is interpreted as arising from an electronic structure where the Fermi level passes through band states having both holes and electrons as indicated by band structure calculations. Below 30 K, the conduction is discussed in terms of weak localization and Kondo effects. The HEA structure appears stable for annealing in vacuum, while annealing in an oxygen-containing atmosphere causes the surface to oxidize and grow a Cr-rich oxide on the surface. This is then accompanied by demixing of the HEA solid solution and a decrease in the effective resistance of the film. [ABSTRACT FROM AUTHOR]

Frequency and voltage dependent electrical characteristics are reported for Ni/ZnO Schottky diodes. Schottky diodes are realized from nano-structured ZnO thin films grown by DC magnetron sputtering. Electrical characterizations are performed by current-voltage (I-V), capacitance-voltage (C-V) and conductance-voltage (G=!-V) measurements. The diode parameters are extracted, such as barrier height (ϕB), ideality factor (n) and carrier concentration (ND). The diodes exhibited a non-linear rectifying behaviour with a barrier height of 0.68 eV and an ideality factor greater than unity. Charge transport mechanism and possible reasons responsible for non-idealities are investigated. The density of interface states (NSS) below the conduction band are extracted from the measured values of I-V and C-V as a function of EC - ESS. From EC - 0:51 to EC - 0:64 eV below the conduction band edge, the interface state density NSS is found to be in the range 1:74 x 1012-1:87 x 1011 eV-1 cm-2. The interface states density obtained from capacitance-frequency (C-f) characteristics varied from 0:53 x 1012-0:12 x 1012 eV-1 cm-2 from EC - 0:82 eV to EC - 0:89 eV below the conduction band. A complete description of current transport and interface properties is important for the realization of good quality Schottky diodes and for the design and implementation of high performance electronic circuits and systems. [ABSTRACT FROM AUTHOR]

The bandstructure of 〈110〉 silicon nano wires (SiNWs) with diameters (d) up to 6.1nm were studied using density functional theory. Three types of surface termination were investigated: H, F, and OH; all giving quantum confinement induced direct bandgaps in the investigated size range. Comparison of the calculated results to reported experimental values showed that trends in the bandstructure behaviour were well reproduced. By studying the relative decrease of global and local minima in the conduction band minimum with increasing d, it was possible to predict a direct-to-indirect bandgap transition at d=9.2, 9.5, and 11.4 nm for H, F, and OH terminated NWs, respectively. [ABSTRACT FROM AUTHOR]