E. N. Bormontov

Influence of water vapor adsorption on the C-V characteristics of heterostructures containing porous silicon

Porous silicon (por-Si) is prepared by the electrochemical etching of single-crystal n-silicon in an aqueous-alcoholic solution of hydrofluoric acid in the presence of hydrogen peroxide oxidizer. The dependence of the high-frequency C-V characteristics of Al/por-Si/Si heterostructures on the relative humidity is studied. A model of capacitor structure is proposed, and a method of analyzing its capacitance as a function of the water vapor partial pressure in terms of the adsorption isotherm is elaborated. Within the framework of this model, the porosity of the material, the effective fraction of silicon dioxide in the por-Si, the fraction of intercommunicating porosity, the micropore-to-mesopore volume ratio, and the mesopore size distribution are determined. The porous silicon prepared in this work seems promising as a sensitive layer in capacitance-type humidity sensors.

Mis structure with polyamide insulator under the conditions of water vapor sorption

A silicon MIS structure with sulfonate-containing aromatic polyamide as a gate insulator is prepared with the aim of using it as a capacitive-type humidity detector. A detector made of this material offers a high sensitivity at an elevated relative humidity and a high speed of response. Measurements of the capacitance of the structure at different frequencies basically make it possible to determine the water distribution in the polymer matrix. The high-frequency (1 MHz) capacitance versus relative humidity dependence (i.e., the calibration curve of the detector) is typical of the isotherms of water vapor sorption by similar polymers.

Adsorption-based porosimetry using capacitance measurements

It is shown that the dependence of capacitance of an Al/por-Si/Si structure on relative humidity is represented as an isothermal curve of physical adsorption. An analysis of this dependence makes it possible to determine the total porosity, the effective fraction of the oxide phase in por-Si, and the ratio between the volumes of micropores (the monomolecular and polymolecular adsorption of water which results in filling of their volume) and mesopores (which are filled according to the mechanism of capillary condensation). The size distribution for mesopores was obtained.

Equilibrium and nonequilibrium electrode processes on porous silicon

The electrode potential of porous silicon (por-Si) in aqueous electrolytes of variable acidity has been measured for the first time. It is shown that por-Si electrode can be a promising pH sensor. The results of the electrode potential measurements show that water condensed in capillaries of capacitive humidity sensors with a thick layer of mesoporous silicon is probably subject to electrolysis.

Charge distribution in a MIS insulator from spectral characteristics of photoemission current

The field dependence of photoemission currents in a MIS structure was derived for the case when the space charge is randomly distributed over the insulating layer. It was found analytically that the position of the top of the potential barrier for electrons photoinjected from the gate into the insulator is defined by the derivative of this barrier with respect to the external field strength. A method for correctly determining the space charge profile in a MIS insulator is suggested. The profile is derived from a family of spectral characteristics taken at different gate voltages. The method is especially suitable for profiling the negative charge in MIS insulators.

Transient spectroscopy of surface states in a constant subthreshold current mode for MIS transistors

The spectrum of surface states at a semiconductor-insulator interface is studied through the relaxation of the gate voltage of an MIS transistor measured with a constant subthreshold current. The proposed method makes permits study of these states in both halves of the semiconductor gap and is convenient for testing integrated circuits. The possibilities of this method are illustrated using the example of radiation induced changes in the distribution of surface states.

Ring voltage controlled oscillator for high-speed PLL systems

A circuit of a ring voltage controlled oscillator (VCO), which is to be used in high-speed phase-locked loop (PLL) systems integrated into programmable logic integrated circuits, is proposed. The maximum operating frequency of a VCO in 180 nm CMOS is shown by simulation to be able to reach 2 GHz in all operating conditions with the phase noise being −99 dB/Hz and detuning frequency being 1 MHz.

Oscillations of the band gap of single-walled carbon nanotubes in the range of very small diameters

The electronic properties of carbon nanotubes with controllable chirality indices are studied in the range of very small diameters (0.3–2.0 nm) of semiconductor single-walled carbon nanotubes. The density functional theory (DFT) in the local density approximation (LDA) (DFT-LDA) method and Gaussian and TubeGen software are used in the study. An unsteady oscillatory variation in the band gap is established. Such behavior is due to the small chirality indices that define the symmetry and curvature of nanotubes. It is found that, for semiconductor nanotubes with very small diameters and (0, 4) and (0, 5) chirality indices, the band structure is degenerate and this degeneracy is responsible for the metal properties and violation of the rule of the 3k classification of single-walled nanotubes according to their electrical properties.

Silicon MOS structures with nonstoichiometric metal-oxide semiconductors

MOS structures are formed by oxidative annealing of tin, tungsten, palladium, nickel, and zinc thin films on silicon, and their high-frequency C-V characteristics are measured. The energy spectra of the density of surface states taken of SnO2 − x, WO3 − x and PdOx nonstoichiometric oxides are found to have common features.

Interaction of metal nanoparticles with a semiconductor in surface-doped gas sensors

A capacitance response of semiconductor sensors fabricated on the basis of thin NiO and SnO2 films with noble-metal nanoparticles deposited on their surface was analyzed. This response was shown to appear due to the solid-phase metal-semiconductor reaction accompanied by the formation of a boundary layer with a fairly high density of surface electron states in its band gap. The chemisorption field effect (the change in work function of the metal after inlet of gases) observed in the capacitance gas sensors not only forms the basis for the sensitive and prompt method of analysis but also represents the basic functional phenomenon responsible for their capacitance response.