The main purpose of this work is to determine the borders of areas with different types of conductivity within homogeneity region of Ga solid solutions in PbTe/Si and PbTe/SiO₂/Si films prepared by modified HWE technique.

The chemical composition of Ga-doped PbTe/Si and PbTe/SiO₂/Si layers was analyzed by the electron probe microanalysis (EPMA) method on JEOL JCA 840 with the help of the energy dispersion (ED) and the wave dispersion (ED) spectrometers using Kα₁ - and Lα₁ - emissions. The electrical parameters of PbTe<Ga> films were evaluated from dc four-probe measurements by Van der Pauw technique and by the investigation of the C - U - curves ("Hg probe" method) also.  As it is known, the oxidation process of A^IVB^VI semiconductors, which intentionally or unintentionally occurs on the surface, affects the electronic properties of these materials greatly. In order to reduce this undesirable influence the silver contact pads were prepared by the thermal deposition in vacuum immediately after the plasma etching of PbTe<Ga>/Si and PbTe<Ga>/SiO₂/Si heterostructures surface through a special mask in Ar atmosphere within the same technological cycle.

The second method of PbTe<Ga>/Si and PbTe<Ga>SiO₂/Si heterostructures preparation offers the direct one stage synthesis, in which the doping and the layer condensation processes proceed simultaneously [3]. The results of high-temperature mass-spectroscopy study have shown that at temperature interval 950 - 1300 K the saturated vapor phase over Ga_1–xPb _x melts is enriched by III A group metal regarding to the Raoult's law [4]. Varying the ratio of partial pressures of the metal components and the chalcogen, it is possible to synthesize Pb_1–zGa _z Te layers (0.0011 < z < 0.08), in which the tellurium content has been varied within the limits from 0.485 up to 0.525 mole fraction.

X-ray, SEM, and EPMA experimental data have demonstrated that the region of homogeneous Pb_1–zGa _z Te films existence was much narrow than indicated interval of Ga concentration in prepared samples [3]. It has been noted that homogeneity region of Ga - solid solutions in PbTe/Si and PbTe/SiO₂/Si is asymmetric regarding to quasibinary PbTe - GaTe cross-section (Fig. 1 a)

The comparison of the electrical parameters results measurements with the region of homogeneous Ga solid solutions in PbTe films existence is presented in Fig. 1 b. It can be seen that the areas with n- and p-types of conductivity exist within homogeneity region of Ga solid solutions in PbTe/Si and PbTe/SiO₂/Si films [5]. Besides, the samples with semi-insolating properties ([n], [p] are about 10¹³ - 10¹⁴ cm^–3 at T = 77 K), which are perspective for fabrication of IR sensors, have been observed. It has been found that the area of existence of PbTe<Ga> films with the semi-insolated properties has the complicated shape. Along PbTe - GaTe and PbTe - Ga₂Te₃ cross-sections the maximum concentration of Ga atoms zGa is approximately 0.0076 ± 0.0005.

References

1. M. Rahim, A. Khiar, M. Fill, F. Felder, H. Zogg. Electron Lett. 18, 1037 (2011).

2. B.A. Volkov, L.I. Ryabova, D.R. Khohlov. Progress in Phys. Sci. (Russ). 172, 875 (2002).

3. S.V. Belenko [et al]. Journ. Surface Investig. X-ray, Synchrotron and Neutron Techn. 4, 170 (2010).

4. A.M. Samoylov [et al]. Russian Journ. General Chem. 81, 27 (2011).

5. A.M. Samoylov, S.V. Belenko, M.K. Sharov, E.A. Dolgopolova, V.P. Zlomanov. Journ. Cryst. Growth. 351, 149 (2012).

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