A. N. Lukin

APPLICATION OF SEMICONDUCTOR GAS SENSORS FOR MEDICAL DIAGNOSTICS

Abstract The appearance of a small amount of acetone vapour (0.1–10 ppm) in the human expiration means exacerbation of diabetes. This form of disease requires special forms of medical treatment and thus the detection of acetone proves to be an actual problem. Moreover, for some sick persons this parameter correlates with the content of glucose in the blood. The aim of this work is to show the principal possibility of the application of semiconductor gas sensors in the diagnosis of diabetes and the development of the prototype of gas analytical instrument based on these sensors.

Investigations of nanodimensional Al2O3 films deposited by ion-plasma sputtering onto porous silicon

The purpose of this study is the deposition of nanodimensional Al2O3 films on the surface of nanoporous silicon and also fundamental investigations of the structural, optical, and morphological properties of these materials. Analyzing the results obtained here, it is possible to state that ultrathin nanostructured Al2O3 films can be obtained in the form of threads oriented in one direction and located at a distance of 300–500 nm from each other using ion-plasma sputtering on a layer of porous silicon. Such a mechanism of aluminum-oxide growth is conditioned by the crystallographic orientation of the initial single-crystalline silicon wafer used to fabricate the porous layer. The results of optical spectroscopy show that the Al2O3/por-Si/Si(111) heterophase structure perfectly transmits electromagnetic radiation in the range of 190–900 nm. The maximum in the dispersion of the refractive index obtained for the Al2O3 film grown on por-Si coincides with the optical-absorption edge for aluminum oxide and is located in the region of ~5.60 eV. This fact is confirmed by the results of calculations of the optical-absorption spectrum of the Al2O3/por-Si/Si(lll) heterophase structure. The Al2O3 films formed on the heterophase-structure surface in the form of nanodimensional structured threads can serve as channels of optical conduction and can be rather efficiently introduced into conventional technologies, which are of great importance in microelectronics and optoelectronics.

Structure and optical properties of thin Al2O3 films deposited by the reactive ion-plasma sputtering method on GaAs (100) substrates

Structural analysis and optical spectroscopy are used to study the properties of ultrathin Al2O3 films deposited in an ion-plasma sputtering installation. It is possible to demonstrate that the technological method used to deposit the films can yield amorphous, smooth, pore-free, and almost homogeneous films in which crystals of the α phase of aluminum oxide Al2O3 nucleate. The films transmit light extremely well in the IR (infrared), visible, and UV spectral ranges and are of potential importance for the development on their basis of antireflection coatings for mirrors of high-power semiconductor lasers based on III–V compounds.

Infrared reflection spectra of multilayer epitaxial heterostructures with embedded InAs and GaAs layers

The effect of the thickness of embedded InAs and GaAs layers on the infrared reflection spectra of lattice vibrations for AlInAs/InAs/AlInAs, InGaAs/GaAs/InGaAs, and AlInAs/InGaAs/GaAs/InGaAs/AlInAs multilayer epitaxial heterostructures grown by MOC hydride epitaxy on InP (100) substrates is studied. Relative stresses emerging in the layers surrounding the embedded layers with variation in the number of monolayers from which the quantum dots are formed and with variation the thickness of the layers themselves surrounding the embedded layers are evaluated.

Infrared reflectance spectra and morphologic features of the surface of epitaxial AlxGa1−xAs/GaAs(100) heterostructures with the ordered AlGaAs2 phase

The infrared reflectance spectra associated with lattice vibrations in the epitaxial AlxGa1−xAs/GaAs(100) heterostructures with different Al content in the cation sublattice are studied. The structures are grown by metal-organic chemical vapor deposition. In the spectrum of the structure with x ≈ 0.50, the vibration modes corresponding to the superstructurally ordered AlGaAs2 phase are detected. The atomic force microscopy of the surface of the sample with x ≈ 0.50 reveals areas of ordered nano-scaled profile, with a period of ∼ 115 nm. The ordered domains involve the AlGaAs2 structured phase.

Optical properties of SnO2−x nanolayers

Specific features in the optical absorption spectra and capacitance-voltage characteristics of SnO2−x nanolayers have been observed. These features are determined by the surface and intergranular states of Sn2+ ions, which appear due to the oxygen deficit and form localized states in the bandgap of SnO2−x. The observed dimensional effect in SnO2−x nanolayers is manifested by an increase in their bandgap width as compared to that in the bulk SnO2.

Experimental studies of the effects of atomic ordering in epitaxial Ga x In1 – x P alloys on their optical properties

The properties of epitaxial GaxIn1 – xP alloys with an ordered arrangement of atoms in the crystal lattice are studied by a number of spectroscopic methods. The alloys are grown by metal-organic chemical vapor deposition onto single-crystal GaAs(100) substrates. It is shown that, under conditions of the coherent growth of an ordered GaxIn1 – xP alloy on a GaAs(100) substrate, atomic ordering results in radical modifications of the optical properties of the semiconductor compared to the properties of disordered alloys. Among these modifications are a decrease in the band gap and an increase in the luminescence intensity. From the data of dispersion analysis of the infrared dispersion spectra and from ultraviolet spectroscopy data obtained in the transmittance–reflection mode of measurements, the basic optical characteristics, specifically, the dispersion of the refractive index and the high-frequency permittivity of GaxIn1 – xP alloys with ordering are determined. All of the experimental data are in good agreement with the developed theoretical concepts.

Effect of Conditions of Electrochemical Etching on the Morphological, Structural, and Optical Properties of Porous Gallium Arsenide

The properties of porous GaAs samples produced by the electrochemical etching of single-crystal n-GaAs(100) wafers are studied by X-ray diffraction analysis, electron microscopy, and infrared and ultraviolet spectroscopy. It is possible to show that, by choosing the composition of the electrolyte and the conditions of etching, samples can be produced not only with different degrees of porosity and pore sizes (nanopores/micropores), but with another type of sample surface as well. The etching of n-GaAs(100) wafers under the conditions chosen in the study does not change the orientation of the porous layer with respect to the orientation of the single-crystal GaAs(100) substrate. At the same time, etching induces a decrease in the half-width of the diffraction peak compared to that for the initial wafer, a splitting of the phonon mode in the infrared spectra and a partial shift of the components in accordance with the parameters of anodic etching, and a change in the optical properties in the ultraviolet region.

Effect of Misorientation and Preliminary Etching of the Substrate on the Structural and Optical Properties of Integrated GaAs/Si(100) Heterostructures Produced by Vapor Phase Epitaxy

It is shown for the first time that the structural and optical functional characteristics of integrated GaAs/Si(100) heterostructures can be controlled by using misoriented Si(100) substrates and their preliminary etching. The growth of an epitaxial GaAs layer on a Si substrate without the formation of antiphase domains can be carried out on a substrate deviated from the (100) singular plane by an angle smaller than 4°–6° or without a transition layer of GaAs nanocolumns. Preliminary treatment of the silicon substrate by etching makes it possible to use it for the vapor-phase epitaxial growth of a single-crystal GaAs film with a considerably smaller relaxation coefficient, which has a positive effect on the structural quality of the film. These data are in good agreement with the results of IR reflectance spectroscopy and photoluminescence and ultraviolet spectroscopy. The features of the optical properties of integrated GaAs/Si(100) heterostructures in the infrared and ultraviolet spectral regions are also defined by the relaxation coefficient.

Growth features and spectroscopic structure investigations of nanoprofiled AlN films formed on misoriented GaAs substrates

Nanostructured aluminum-nitride films are formed by reactive ion-plasma sputtering onto GaAs substrates with different orientations. The properties of the films are studied via structural analysis, atomic force microscopy, and infrared and visible–ultraviolet spectroscopy. The aluminum-nitride films can have a refractive index in the range of 1.6–4.0 at a wavelength of ~250 nm and an optical band gap of ~5 eV. It is shown that the morphology, surface composition, and optical characteristics of AlN/GaAs heterophase systems can be controlled using misoriented GaAs substrates.