A. M. Samoilov

Electrical properties of thin PbTe films on Si substrates

An attempt was made to reduce the carrier concentration in thin PbTe films on Si substrates by optimizing deposition conditions. A modified hot-wall method was used for reproducible growth ofp-type films with 5 × 1015 < p(77 K) < 5 × 1017 cm-3 andn-type films with 3 × 1015 < n(77 K) < 5 × 1016 cm-3. The IR irradiation was found to have a significant effect on the temperature variation of film resistance. The activation energy of the IR-sensitivity centers was determined to be 0.11 ± 0.005 eV at room temperature and 0.18 ± 0.005 eV between 150 and 180 K.

Transport Properties of Ga-Doped PbTe Thin Films on Si Substrates

Thin PbTe films on Si substrates were doped with Ga via annealing in the vapor produced by heating a Ga(l) + GaTe(s) mixture (GaTe(s) + L1+ Vequilibrium). Electrical measurements showed that the vapor-phase doping reduced the hole concentration in the films by more than two orders of magnitude. IR irradiation was found to reduce the resistivity of the PbTe films by a factor of 40–100. The films annealed in the vapor over GaTe(s) + L1for the longest time exhibited an anomalous temperature variation of resistance, which was interpreted as due to the limited Ga solubility in PbTe.

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.

Structure of heterosystems formed by a SnO2 film and island metal (Ag, Au, or Pd) condensate

We have studied the phase composition and microstructure of thin tin(IV) oxide films surfacemodified with silver, gold, and palladium nanoislands. Using high-energy electron diffraction, we have shown for the first time that the thermal oxidation of the Sn films leads to the formation of nanocrystalline multiphase SnO2 films in which the major phase is orthorhombic. Also present are (in order of decreasing content) tetragonal and cubic phases. Blocks of SnO2(O) subgrains with 〈101〉 texture contain dislocations and stacking faults, which are interpreted as layers of the tetragonal phase. It has been shown that vacuum condensation makes it possible to modify the surface of SnO2 films with noble metals and obtain homogeneous nanoisland coatings characterized by a unimodal, uniform island size distribution.

Ga Doping of Thin PbTe Films on Si Substrates during Growth

In depositing thin PbTe films onto Si substrates by a modified hot-wall method, Pb1 – xGax melts were used as Ga vapor sources in combination with separate Pb and Te sources. Data on the vaporization behavior of Pb1 – xGax melts were used to devise a new technique for reproducible growth of PbTe/Si and PbTe/SiO2 /Si structures. The lattice parameter of the PbTe films was found to vary nonmonotonically with Ga content, which was interpreted as evidence that the dopant can be incorporated by different mechanisms. Conductivity and Hall effect measurements between 77 and 300 K reveal a nonmonotonic variation of carrier concentration with doping level and suggest that Ga is an amphoteric impurity in narrow-gap IV–VI semiconductors.

Growth of In-Doped PbTe Films on Si Substrates

Data on the evaporation behavior of Pb1 – xInx (0.10 ≤ x ≤ 0.70) melts were used to devise a procedure for the growth of vapor-phase In doped PbTe thin films on Si substrates. This approach offers the possibility of growing single-phase, homogeneous Pb1 – yInyTe films of controlled composition by adjusting the composition and temperature of Pb1 – xInx (0.10 ≤ x ≤ 0.50) melts. X-ray diffraction characterization demonstrates that the films grown on Si with no oxide layer consist of slightly misoriented crystallites, with their (100) axes normal to the film surface, whereas the films grown on substrates covered with a SiO2 layer are polycrystalline, with a strong (100) texture.

Synthesis of films in the system Ga–Pb with precision control over quantitative composition

According to high-temperature differential mass spectrometry, analytical form of the dependence of structure of the saturated vapor composition over melts of the system Ga–Pb on partial pressures of components and total pressure in the system was determined. On the basis of this dependence, taking into account corrections for the deviations from thermodynamic equilibrium conditions in the reaction cell, the scientifically-proved method of the synthesis of GayPb1–y (y = 0.002–0.050) films with precision control over their quantitative composition structure was developed.

The Region of gallium solubility in lead telluride films grown on silicon substrates

This work is aimed at finding the boundaries of the region of the existence of the solid solutions of Ga in PbTe films prepared on Si substrates with the use of the modified “hot wall” technique. The quantitative results on the composition of the Pb1-y GayTe films with a thickness of more than 1 µm indicate that the gallium concentration yGa in our samples ranges from 0.0004 yGa0.045, depending on the ratio of the partial pressures of the metallic components, which maybe specified by the temperature and composition of the Ga1–xPbx liquid melts. By varying the partial pressures of the metallic components and the chalcogen, we succeeded in synthesizing Pb1-yGayTe layers with a Te concentration ranging from 0.495 to 0.515 mol %. According to the results of a complex investigation with the use of X-ray diffraction, scan ning electron microscopy, and local X-ray spectrum analysis, the region of the existence of homogeneous Pb1 - y GaTe films is substantially narrower than the specified composition range: the limiting Ga concentration in these samples is no more than yGa = 0.011 ± 0.0005. It has been shown that the study of gallium solubility in PbTe should include not merely a quasi-binary PbTe-GaTe section, but also PbTe-Ga2Te3 and PbTe-Ga2Te5 polythermic sections. As indicated by the experimental data, the homogeneity region of the solid solutions of gallium in lead telluride is asymmetric with respect to the quasi-binary PbTe-GaTe section. It has been found that the deviation of the Pb1-yGayTe films from stoichiometry toward excessive concentration of tellurium promotes increased solubility of gallium in the lead telluride matrix.

Codeposition of Metallic Components in the Growth of Thin PbTe〈Ga〉 Films on Si Substrates

In depositing thin PbTe〈Ga〉 films onto Si and SiO2 /Si substrates by the hot-wall method, Pb1 – xGaxmelts were used as Ga vapor sources in combination with separate Pb and Te vapor sources. The vaporization of Pb1 – xGax(0.15 ≤ x≤ 0.95) melts was studied between 1000 and 1300 K in the reaction chamber of the deposition unit. Using electron probe x-ray microanalysis, all the deposited films were shown to contain Ga. Pb1 – xGaxmelts were also used as separate Pb and Ga vapor sources.