Silicon-germanium alloy films were formed by electrochemical deposition of germanium into porous silicon matrices with thicknesses varying from 1.5 to 10 mu m followed by subsequent rapid thermal processing at 950 degrees C in an inert atmosphere. Study of the fabricated structures using SEM and Raman spectroscopy, as well as measurements of their electrical conductivity and thermoelectric properties revealed that the highest Seebeck coefficient (-505 mu V/K at 450 K) and Power Factor (1950 mu W/(m & sdot;K2) at 400 K) values were obtained when a 5 mu m-thick porous silicon was used as a structural matrix. Under such conditions, an optimal balance between electrical conductivity, structural disorder and electrical insulation from the substrate is achieved due to the presence of a residual porous underlayer, making it possible to maximize the film's thermoelectric performance. The obtained silicon-germanium alloy films are deemed suitable for the fabrication of both discrete and integrated thermoelectric devices based on monocrystalline silicon substrates.

Thermoelectric materials based on cobalt-containing SiGe alloy films were fabricated using monocrystalline silicon wafers with thin porous silicon layers electrochemically decorated with cobalt nanoparticles, filled germanium and subsequently subjected to rapid thermal processing. SEM, XRD, Raman spectroscopy and measurements of electrical conductivity and thermoelectric parameters revealed that an intermediate silicidization step involving thermal processing at 850 degrees C after cobalt deposition is crucial to maximize the resulting alloy's thermoelectric capabilities. The obtained silicidized SiGe:Co samples demonstrate a Seebeck coefficient of -450 mu V/K and an estimated figure-of-merit ZT value of up to 0.72 at 450 K due to the presence of crystalline cobalt silicides in the film. These results enable a new approach to the fabrication of thin film thermoelectric materials based on SiGe alloys.

Film structures based on Si1–xGex (0 < x < 1) solid solutions are currently obtained by chemical-vapor-deposition methods. For device application of the obtained structures, it is necessary to know the electrical properties of the material synthesized under different conditions. In this work, we carry out galvanomagnetic studies of the electrical conductivity in porous and solid Si1–xGex films, as well as the concentration and mobility of the majority charge carriers in them at a temperature of 30–300 K. It is shown that, as in pure silicon and germanium of comparable porosity, the electrical conductivity in the studied samples can be considered as in a medium with voids. It is established that the type of majority charge carriers in the alloy is determined by the type of silicon substrate used. This is practically important for creating both arms of a thermoelectric converter, which makes the method for producing Si1–xGex(0 < x < 1) alloy promising for device applications, in particular in thermoelectric converters and lithium-ion batteries.

A variety of micro‐ and nanocomposite materials based on electrochemically‐acquired porous silicon are produced and evaluated in terms of their applicability to display technology. It is shown that porous silicon provides a versatile and well‐adjustable template for filling with other materials, which can outright change its electrophysical parameters. While, in terms of display applications, porous silicon layers are mostly prominent for their photohiminescence not akin to monocrystalline silicon, this property can be additionally enhanced by employing a variety of electrochemical techniques to form metal deposits of certain shapes.

Morphology and crystalline structure of silicon-germanium alloys formed by rapid thermal processing of germanium-filled porous silicon layers are evaluated. Two types of porous silicon are employed as matrices for electrochemical pore filling using GeO2 aqueous solutions and subsequently compared, the first one formed by electrochemical anodization and the second by silver-assisted chemical etching of monocrystalline silicon. The resulting alloys' structure and composition are investigated using scanning electron microscopy, energy -dispersive X-ray analysis, Raman spectroscopy and X-ray powder diffraction. It is shown that by varying the porosity of the initial matrix (by adjusting anodization current density for anodic porous silicon or changing silver deposition time for structures produced by metal-assisted etching) in the range from 55 to 75%, Si1-xGex alloys with germanium fractions of x = 0.31 to x = 0.83 can be formed, as indicated by Raman spectroscopy. It is concluded that composition-adjustable layers of silicon-germanium can be successfully formed on either type of porous silicon layer. While an increase in porosity generally leads to a decrease in silicon fractions in the alloy, the steepness of this effect varies heavily depending on the type of porous matrix used and should be considered independently for anodic porous silicon and silicon nanowires.

Using scanning electron microscopy, the structures of the surface and internal regions of porous silicon obtained by anodizing heavily doped plates of single-crystal silicon with electron conductivity in a hydrofluoric acid solution at different current densities were studied. It is found that the porous silicon surface has dark gray and light gray pores, which differ in size and surface distribution density. Dark gray pores possess larger sizes, and their density is about 5–10 times less than that of light gray pores. Based on the cross-section imagery, it is shown that light gray pores correspond to underdeveloped channels of small depth, while dark gray pores are the entrance points of deep bottle-shaped channels passing from the surface into the depth of the silicon wafer. The equivalent diameters of light gray pores on the surface of porous silicon are 12–15 nm and are practically independent of the anodic current density. At the same time, the equivalent diameters of dark gray pores and average distances between their centers increase linearly from 15 to 35 nm on the surface and from 35 to 120 nm in the volume of porous silicon when the current density is increased from 30 to 90 mA/cm2. The average thickness of silicon skeleton elements is about 3 nm on the surface and increases to 5–6 nm in the volume. By setting the density of the anode current, it is possible to obtain layers of porous silicon with different structural parameters. The obtained research results have practical significance for the formation of composite materials based on porous silicon, which can be used as a porous matrix for the deposition of metals and semiconductors.

Morphology and crystalline structure of silicon-germanium alloys formed by rapid thermal processing of germanium-filled porous silicon layers are evaluated. Two types of porous matrices are used for electrochemical pore filling using GeO2 aqueous solutions and subsequently compared, the first one formed by electrochemical anodization and the second by metal-assisted chemical etching of monocrystalline silicon. The resulting alloys’ structure and composition are investigated using scanning electron-microscopy, Raman spectroscopy and X-ray powder diffraction. It is concluded that layers of silicon-germanium can be successfully formed on either type of porous layer, exhibiting some minor distinctions in uniformity but no major difference between the resulting alloys’ composition.

A method of germanium electrodeposition from a GeO2-based aqueous solution into the pore channels of anodic mesoporous silicon formed on n-type highly-doped (100) silicon wafers is described. The effect of deposition time, pore channel shape and preconditioning of porous silicon layers in hydrofluoric acid is evaluated. Recommendations are given in regards to the optimal parameter combinations to ensure uniform pore channel filling with germanium. The possibility of producing silicon-germanium alloys by subsequent rapid heat treatment of the germanium-filled porous silicon layers is established.

In this work, we propose a new, previously unpresented in the literature, approach to the formation of Si1-xGex films. This approach includes electrochemical processes of the formation of porous silicon, electrochemical deposition of low-melting metals and Ge. Post-heat treatment is made possible to synthesize film structures based on Si1-xGex solid solutions. Using this approach an alloy of the composition Si0.4Ge0.6 has been obtained at a lower formation temperature than predicted by the phase diagram for the Si-Ge system.

Indium electrodeposition in-between silicon nanowire arrays fabricated by silver-assisted chemical etching of lightly-doped (100)-oriented silicon wafers is evaluated. It is concluded based on SEM and EDX analysis of indium’s distribution that, by utilizing pulsed-mode electrodeposition and maintaining a sufficiently low duty cycle value, indium particles can be formed exclusively at the very bottom of each consecutive pore on the residual silver particles left over from metal-assisted etching. This result differs significantly from irregular pore filling along with surface and subsurface deposition observed in the cases of continuous galvanostatic deposition regimes at prolonged durations or in the absence of residual silver particles. Bottommost fusible metal deposit localization, which is unattainable on porous silicon fabricated by electrochemical anodization, is presumed to be optimal for the growth of germanium crystallites inside the pores via the electrochemical liquid-liquid-solid approach and subsequent silicon-germanium alloy formation through thermal annealing.

The regularities of composition changes of silicon/germanium alloy thin films formed on a monocrystalline silicon substrate by electrochemical deposition of germanium into a porous silicon matrix with subsequent rapid thermal annealing (RTA) at a temperature of 750–950°C are studied. An analysis of the samples by Raman spectroscopy showed that an increase of RTA temperature leads to a decrease in the germanium concentration in the formed film. A decrease of the RTA duration at a given temperature makes it possible to obtain films with a higher concentration of germanium and to control the composition of thin silicon/germanium alloy films formed by changing the temperature and duration of RTA. The obtained results on controlling the composition of silicon/germanium alloy films can be used to create functional electronic devices, thermoelectric power converters, and optoelectronic devices.

Various cases of electrochemical deposition of indium into oxidized and unoxidized mesoporous silicon were investigated and subsequently compared. The results would suggest that both thermal and chemical oxidation of porous silicon cause the metal particles being deposited into its pores to shift deeper along the pore channels due to the latter's topmost areas being oxidized the most and therefore becoming significantly less conductive and more easily wettable by both the deposition solution and indium itself upon its subsequent thermal processing. However, oxidation becomes less effective as the thickness of the porous layer is increased due to the gradually escalating effect of reduced conductivity at the pore tips. Potentially, porous silicon layers with indium particles localized in the bottommost parts of the pore channels could be used to form germanium nanostructures inside the pores, allowing subsequent creation of Ge-Si alloys by utilizing the electrochemical liquid-liquid-solid approach.

It is concluded that oxidation of porous silicon in an air atmosphere at 300 ° C or in an aqueous solution of nitric acid (50 vol.%) can drastically improve the filling of pores by indium during its subsequent electrochemical deposition. Due to the oxidation of the porous skeleton’s topmost areas, the maximum concentration of indium is shifted from the surface deeper into the pore channels. This effect is especially apparent in the case of oxidation via nitric acid, whereat the maximum relative concentration of indium inside the pores is achieved.

The oxidation of scaffold of porous silicon in air at 300°C or an aqueous HNO 3 solution (50 vol %) is found to improve pore filling in electrochemical deposition of indium into it. Due to incomplete oxidation of the porous silicon scaffold, the peak in indium concentration shifts away from the surface, deeper into the porous layer. The greatest effect—the highest indium concentration in pores—is observed for porous silicon oxidized in the HNO 3 solution.

The influence of silicon wafer crystallographic orientation on the formation of porous silicon during anodization in an HF solution is studied. Cross-section SEM image comparison of samples with different crystallographic orientations has shown that (111) Si samples exhibit a more branching, tree-like pore structure with a higher porosity value compared to (100) Si samples. This phenomenon is explained by pointing out differences in crystal structure and numbers of Si-Si chemical bonds in different crystallographic directions. Namely, in (100)-oriented silicon crystals every surface Si atom has two bonds connecting it to atoms underneath it, as well as two broken bonds able to interact with Fions. Through electron injection into silicon, enough energy is applied to break the underlying bonds, forming SiF as a result. The presence of two Fions bonded with every surface silicon atom leads to weakening the bonds of surface silicon atoms with the underlying atoms, thus making the process of breaking the Si-Si bonds more energy efficient. As for (111)-oriented crystals, silicon atoms only have one broken surface bond, and breaking backbonds with underlying silicon atoms requires a higher value of activation energy due to their larger amount (three as opposed to two for (100) silicon). It is concluded that this very reason leads to slower etching speeds of (111)-oriented silicon wafers. The results help evaluate the way the silicon crystal structure affects the etching process, including its speed and direction, which is an especially important factor to consider when forming (111)-oriented porous silicon.

Silicon nanowires (SiNWs) were comprehensively characterized in dependence on conditions of their formation via metal (Ag) -assisted chemical etching (MACE) of monocrystalline Si. The Ag structures remained on/between SiNWs based on both n- and p-Si were found to promote surface enhancement of Raman scattering (SERS) from organic molecules adsorbed on their surface. The Ag structures on/between the SiNWs/p-Si facilitated two times higher SERS-signal from 10_-6 M rhodamine 6G than those in the SiNWs/n-Si. The activity of the SERS-substrates based on p-Si was improved by modification with small Au dendrites, which provided rich family of hot spots and prevented degradation of the SERS-activity observed for pure Ag dendrites due to formation of Ag2S during one week of storage in air. The SERS-substrates based on the Au/Ag dendrites on SiNWs/p-Si allowed to achieve nanomolar detection limit of rhodamine 6G and 5,5 -dithiobis (2-nitrobenzoic acid).

The influence of silicon wafer crystallographic orientation on the formation of porous silicon during anodization in an HF solution is studied. Cross-section SEM image comparison of samples with different crystallographic orientations has shown that (111) Si samples exhibit a more branching, tree-like pore structure with a higher porosity value compared to (100) Si samples. This phenomenon is explained by pointing out differences in crystal structure and numbers of Si-Si chemical bonds in different crystallographic directions. Namely, in (100)-oriented silicon crystals every surface Si atom has two bonds connecting it to atoms underneath it, as well as two broken bonds able to interact with Fions. Through electron injection into silicon, enough energy is applied to break the underlying bonds, forming SiF as a result. The presence of two Fions bonded with every surface silicon atom leads to weakening the bonds of surface silicon atoms with the underlying atoms, thus making the process of breaking the Si-Si bonds more energy efficient. As for (111)-oriented crystals, silicon atoms only have one broken surface bond, and breaking backbonds with underlying silicon atoms requires a higher value of activation energy due to their larger amount (three as opposed to two for (100) silicon). It is concluded that this very reason leads to slower etching speeds of (111)-oriented silicon wafers. The results help evaluate the way the silicon crystal structure affects the etching process, including its speed and direction, which is an especially important factor to consider when forming (111)-oriented porous silicon.