Search

Nanowires represent numerous opportunities for nanoelectronics and sensorics, while metal contact fabrication makes the device development rather challenging. Here, we demonstrate that silicon (Si) nanowires deposited on interdigital metal contacts via simple drop casting exhibit an abrupt increase in conductivity upon exposure to ammonia vapors and aqueous solutions due to adsorption of the analyte species. To reduce the noise of the DC resistance measurements lacking ohmic conductivity, we exploit electronic impedance spectroscopy. The resistive response is found to be dependent on the ammonia content in vapor and liquid matter. The results demonstrate a detection limit of 4 μmol·L–1 (80 ppb), a sensitivity of 0.2% μmol–1·l (0.01%·ppb–1), and applicability for the low-concentration detection of up to 400 μmol·L–1 (8 ppm) ammonia in aqueous solutions both directly and indirectly with a response rate of up to 0.43%·s–1 and a recovery rate of 0.31%·s–1 and show selectivity to oxidizing species. Thus, we demonstrate that the use of semiconductor nanowires in adsorption sensorics does not require the fabrication of ohmic contacts and present a simple fabrication protocol perspective for the development of highly sensitive room-temperature multi-environment sensors. [ABSTRACT FROM AUTHOR]

A method to form tapered structures via the cyclic plasma-chemical etching of silicon using a spherical photoresist mask is described. The method is based on the possibility of controlling the structure profile by adjusting the silicon and photoresist etching selectivity. In this study, to control the selectivity value, each cycle of the well-known two-stage Bosch silicon etching process is supplemented with a third stage, namely, photoresist etching in oxygen-containing plasma. A model of transformation of the photoresist-mask contour during etching is developed using the experimental results. The parameters of the additional stage are calculated for each silicon etching cycle in terms of model concepts. The result is the formation of tapered structures with a sidewall taper angle close to the target value. [ABSTRACT FROM AUTHOR]

Micro‐ and nanostructured silicon surface application is a promising way of photovoltaic development. An enhancement of optical absorption in solar cells can be achieved, for example, using vertically aligned silicon nanostructures with high aspect ratios. Cryogenic plasma etching is a suitable method for such structures' formation; however, there is still lack of data describing an effect of cryogenic inductively coupled plasma (ICP) etching on defect formation in silicon (Si). The defects may act as recombination centers, leading to solar cell characteristics degradation. Herein, the cryogenic dry etching effects on defect formation in float‐zone (FZ) n‐type silicon substrates and on the photovoltaic properties of solar cells made of plasma‐etched silicon substrate are presented. The decrease in low‐injection minority carrier lifetime in silicon from 0.85 to 0.55 ms is observed by photoluminescence decay after the ICP dry etching at −140 °C. This leads to an open‐circuit voltage drop for the (p)a‐Si:H/(n)c‐Si/(n)a‐Si:H heterojunction structure from 680 to 630 mV. A detailed study of the defect properties by deep‐level transient spectroscopy (DLTS), numerical simulation, and its behavior after wet etching and thermal annealing is presented. [ABSTRACT FROM AUTHOR]

Micro‐ and nanostructured silicon surface application is a promising way of photovoltaic development. An enhancement of optical absorption in solar cells can be achieved, for example, using vertically aligned silicon nanostructures with high aspect ratios. Cryogenic plasma etching is a suitable method for such structures' formation; however, there is still lack of data describing an effect of cryogenic inductively coupled plasma (ICP) etching on defect formation in silicon (Si). The defects may act as recombination centers, leading to solar cell characteristics degradation. Herein, the cryogenic dry etching effects on defect formation in float‐zone (FZ) n‐type silicon substrates and on the photovoltaic properties of solar cells made of plasma‐etched silicon substrate are presented. The decrease in low‐injection minority carrier lifetime in silicon from 0.85 to 0.55 ms is observed by photoluminescence decay after the ICP dry etching at −140 °C. This leads to an open‐circuit voltage drop for the (p)a‐Si:H/(n)c‐Si/(n)a‐Si:H heterojunction structure from 680 to 630 mV. A detailed study of the defect properties by deep‐level transient spectroscopy (DLTS), numerical simulation, and its behavior after wet etching and thermal annealing is presented. [ABSTRACT FROM AUTHOR]

Atmospheric pressure plasma technologies are a potential substitution for wet chemical and vacuum processes in the production of crystalline silicon solar cells, leading to a simplified in-line processing chain. In this contribution, a plasma chemical etching technology is presented as a basic step for a future continuous production process. A linearly extended DC arc discharge is used for activation of the etching gases. An Ar-N2 mixture is fed through the plasma source; etch gases are injected into the afterglow plasma, near the substrate. Controlled purge gas systems prevent the contamination of the reaction zone with air or moisture as well as the release of reaction products. The plasma source was studied by a noninvasive in-line monitoring of the DC arc phenomena. Silicon etching rates can be controlled by the etch gas composition and the plasma conditions. Fourier Transform infrared spectroscopy of the waste gas was applied to monitor the current etching rates. First industrial tests confirmed standard efficiencies of the cells after edge isolation by atmospheric pressure plasma etching. [ABSTRACT FROM AUTHOR]

Mixers based on superconductor–insulator–superconductor (SIS) tunnel junctions are the best input devices at frequencies from 0.1 to 1.2 THz. This is explained by both the extremely high nonlinearity of such elements and their extremely low intrinsic noise. Submicron tunnel junctions are necessary to realize the ultimate parameters of SIS receivers, which are used as standard devices on both ground and space radio telescopes around the world. The technology for manufacturing submicron Nb–AlN–NbN tunnel junctions using electron-beam lithography was developed and optimized. This article presents the results on the selection of the exposure dose, development time, and plasma chemical etching parameters to obtain high-quality junctions (the ratio of the resistances below and above the gap Rj/Rn). The use of a negative-resist ma-N 2400 with lower sensitivity and better contrast in comparison with a negative-resist UVN 2300-0.5 improved the reproducibility of the structure fabrication process. Submicron (area from 2.0 to 0.2 µm2) Nb–AlN–NbN tunnel junctions with high current densities and quality parameters Rj/Rn > 15 were fabricated. The spread of parameters of submicron tunnel structures across the substrate and the reproducibility of the cycle-to-cycle process of tunnel structure fabrication were measured. [ABSTRACT FROM AUTHOR]

This article presents the results of a computer simulation of whispering gallery modes in the structure of a silicon disk resonator with a wedge-shaped profile made on a silicon-on-isolator base (SOI). The rationale for the choice of silicon as a material for its manufacturing is given. The results of the study of the influence of the wedge angle on the whispering gallery mode parameters (WGM) are presented. The optimum wedge angle of a silicon disk resonator is determined, which ensures the minimum loss and maximum mode stability. The technological aspects of plasma-chemical etching processes for forming a wedge-shaped profile of the edge of a silicon disk resonator are studied. [ABSTRACT FROM AUTHOR]