A. M. Khoviv

Crystal structure, carrier concentration and IR-sensitivity of PbTe thin films doped with Ga by two different methods

Abstract The comparison of the results of chemical composition, crystal structure, electronic properties and infrared photoconductivity investigations of PbTe/Si and PbTe/SiO2/Si heterostructures doped with Ga atoms by two different techniques is presented in this work. One of these techniques is principally based on the vapour-phase doping procedure of PbTe/Si and PbTe/SiO2/Si heterostructures, which were previously formed by the modified “hot wall” technique. The second method of PbTe(Ga)/Si and PbTe(Ga)/SiO2/Si heterostructure preparation is based upon the fabrication of lead telluride films, which have been doped with Ga atoms in the layer condensation process directly. The lattice parameter and charge carrier density evolutions with the Ga impurity concentration show principally the different character of PbTe(Ga)/Si films prepared by these techniques. It has been proposed that complicated amphoteric (donor or acceptor) behaviour of Ga atoms may be explained by different mechanisms of substitution or implantation of impurity atoms in the crystal structure of lead telluride.

Growth of niobium oxide films on single-crystal silicon

Abstract200-nm-thick niobium films grown on single-crystal silicon wafers by magnetron sputtering have been oxidized by annealing in flowing oxygen. X-ray diffraction examination revealed the metal-like phase Nb6O in the as-deposited films. Annealing in flowing oxygen for 1 h led to the formation of tetragonal NbO2 at 570 K and hexagonal Nb2O5 at temperatures above 770 K. The grain size and surface roughness of the films were evaluated using atomic force microscopy.

Effect of vacuum annealing on the phase composition of In/SnO/Si, In/SnO2/Si, and Sn/In2O3/Si heterostructures

The chemical interaction between indium and thin SnO and SnO2 films and between tin and thin In2O3 films during vacuum annealing was studied. The metallic films were deposited onto single-crystal silicon substrates by magnetron sputtering, the SnO and SnO2 films were produced by heat-treating the Sn film in flowing oxygen at 673 and 873 K, respectively, and the In2O3 film was produced by heat-treating the In film at 573 K. The results indicate that annealing of the In/SnO/Si and In/SnO2/Si heterostructures in vacuum (residual pressure of 0.33 × 10−2 Pa) at 773 K gives rise to the reduction of Sn and oxidation of In, whereas annealing of Sn/In2O3/Si causes partial tin substitution for indium in the cubic indium oxide lattice.

Growth of ultrathin Nb2O5 films on quartz substrates

Niobium oxide films have been grown by reactive rf sputtering in a vacuum system and characterized by absorption spectroscopy and X-ray diffraction. The thickness of the (optically transparent) films has been determined as a function of sputtering time by examining interference effects in a plane-parallel layer. The average deposition rate is determined to be 7.4 ± 0.3 Å/min (95% confidence interval).

Phase composition and electrical conductivity of indium tungstate films produced from bilayer structures

Indium tungstate films have been synthesized via oxidation of indium and tungsten layers deposited on crystalline silicon and fused quartz substrates by magnetron sputtering. The structure and electrical properties of the films have been analyzed in relation to the oxidation procedure, which is shown to have a strong effect on the phase composition of the films. The dc conductivity of the films exhibits inverse Arrhenius behavior.

Oxidation of thin films of zirconium and Zr-Ti solid solutions on single-crystal silicon

We have studied the oxidation of thin films of zirconium and Zr-Ti (1.2–2.03 at % Ti) solid solutions produced on single-crystal silicon wafers by magnetron sputtering. The films have been oxidized in flowing oxygen at temperatures from 473 to 673 K in a resistance furnace. The phase composition of the resultant oxide layers has been determined. Our results indicate that the oxidation kinetics of thin-film zirconium and Zr-based solid solutions are well represented by a linear-parabolic rate law. The composition, structure, and optical constants of the oxide layers depend on the heat-treatment conditions and the titanium content of the films.

Lead titanate ferroelectric films on single-crystal silicon

This paper reports on the results of investigations into the phase transformations observed in Pb/Ti/Si and Ti/Pb/Si thin-film heterostructures upon layer-by-layer magnetron sputtering of lead and titanium onto a single-crystal silicon substrate and subsequent annealing in an oxygen atmosphere. It is shown that the dielectric properties of lead titanate films depend on the order of sputtering of lead and titanium metal layers onto the surface of single-crystal silicon. The ferroelectric properties are revealed in 3000-nm-thick lead titanate films prepared by two-stage annealing of the Pb/Ti/Si thin-film heterostructure (with the upper lead layer) at T1=473 K and T2=973 K for 10 min. These films are characterized by the coercive field Ec=4.8 kV/cm and the spontaneous polarization Ps=16.8 µC/cm2. The lead titanate films produced by annealing of the Ti/Pb/Si thin-film heterostructure (with the upper titanium layer) do not possess ferroelectric properties but exhibit properties of a conventional dielectric.

Pb and In Codeposition in the Vacuum Growth of PbTe Films on Si Substrates

Pb1 – xInx melts were proposed to be used as In vapor sources, in combination with separate Pb and Te sources, in depositing PbTe<In> films onto Si substrates by a modified hot-wall method. Under the assumption that the presence of Pb in Pb1 – xInx melts may raise the In partial pressure, the vaporization behavior of Pb1 – xInx (0.05 ≤ x ≤ 0.70) was studied between 900 and 1200 K in the reaction chamber of the deposition unit. Using electron probe x-ray microanalysis and x-ray diffraction, all the deposited films were shown to contain In. The In content of the Pb1 – yIny deposits varied in the range 0.002 <y < 0.07 and increased with increasing In concentration in the Pb1 – xInx melt and with increasing vapor source temperature. The vapor over molten Pb1 – xInx was shown to exhibit a positive deviation from ideality.

Growth and structure of PbWO4 films

Lead tungstate films have been grown on silicon by magnetron sputtering followed by heat treatment at various temperatures. The thermal oxidation of metal-oxide (Pb/WO3/Si and W/PbO2/Si) and metal-metal (Pb/W/Si) bilayer systems at temperatures above 870 K yields films that are dominated by monoclinic PbWO4 and contain WO3, also monoclinic. The optimal configuration for PbWO4 synthesis is Pb/WO3/Si because, even during lead deposition onto tungsten oxide, we observe the formation of lead tungstate, PbWO4, and subsequent heat treatment increases the percentage of this phase in the film.

Phase Composition and Optical Properties of Thin Films Based on Lanthanum and Tungsten Oxides

We have studied the phase composition and optical properties of 150-to 500-nm-thick films based on lanthanum and tungsten oxides, produced by magnetron sputtering followed by heat treatment at 773 K in vacuum and flowing oxygen. The oxide films have been found to have high transmission in the range 250 to 900 nm and an absorption band between 190 and 250 nm. Analysis of their absorption edge indicates that its complex structure is due to the presence of several phases. The energies of direct transitions evaluated from the spectra of the films coincide with the band gaps of the phases present in the films.