Table 1. The comparison of the estimated data z*_Ga and the real experimental results z_Ga concerning the concentration of Ga atoms in Pb_1–zGa_zTe films fabricated by the improved one stage synthesis. 

The thin films and single crystals of PbTe doped with Ga are the perspective materials for fabrication of the optoelectronic devices employed in infrared (IR) radiation middle wave range [1]. The IR sensitivity of these materials is similar to that of Cd_1–xHg_xTe but processing procedures are much less demanding. Under influence of the presence of III A group metals the energy spectrum of PbTe and its solid solutions can change significantly and depends not only the concentrations of the impurity atoms but from the method of investigated samples synthesis also [2]. 

The main purpose of this work is to emphasize the improvements of Ga-doped PbTe films one stage synthesis with predicted concentration of the impurity atoms by modified HWE technique. Earlier, Ga-doped PbTe thin films on Si-substrates had been prepared by the two stage procedure [3]. This doping procedure was based on the two-zone annealing in atmosphere of the saturated vapor, which corresponds th the three-phase equilibrium L1 + GaTe(S) + V in Ga - Te binary system, of the undoped PbTe/Si heterostructures previously formed by modified HWE technique. The EPMA and XPS experimental results clear demonstrated that after this treatment Ga impurity atoms have distributed on the surface layers quiet irregular. Later, another method of PbTe<Ga> heterostructures preparation was created. This procedure offers direct one stage synthesis, in which the doping and the layer condensation processes proceed simultaneously [4]. Despite the greater difference in fugitives between pure Pb and Ga the results of high-temperature mass-spectroscopy study have shown that saturated vapor phase over Ga_1–xPb _x is enriched with IIIA group metal at temperature interval T = 980 - 1300 K [5].

Fig. 1. The dependence of Ga atoms concentration in saturated vapor over Ga_1–xPb_x melts x^V_Ga upon the values of Ga partial pressure p_Ga and the integral pressure P_int of all components in Ga - Pb binary system.

At the first step of this work the mass-spectroscopic experimental data [5] allow us to determine the concentration of Ga atoms in the saturated vapor over Ga_1–xPb _x melts x^V_Ga dependence upon the values of Ga partial pressure p_Ga and the integral pressure P_int of all components in Ga - Pb binary system (Fig. 1). For x^V_Ga - p_Ga - and x^V_Ga - P_int - projections of the convolute shown in Fig. 1 it has been established that concentration of Ga atoms in equilibrium vapor phase may be expressed by the equations:

x^V_Ga(p_Ga) = A₁ + B₁×exp(C₁×p_Ga)                            (1a)

x^V_Ga(P_int) = A₂ + B₂×exp(–C₂×P_int)                         (1b)

At the second step by the general solution of the equations (1a) and (1b) the regimes (the values of p_Ga, p_Pb, P_int, temperature T, and compositions of initial Ga_1–xPb_x melts) of Ga_1–yPb_y binary layers have been defined. The synthesis of Ga_1–yPb_y samples is necessary to evaluate the degree of the discrepancy from the thermodynamic equilibrium in the HWE reaction chamber. The results of EPMA have shown that in prepared Ga_1–yPb_y binary layers Ga atoms concentration is higher than x^V_Ga. In order to take into account the major part of physicochemical processes resulting in the discrepancy from the thermodynamic equilibrium the analitical equation of factor K₁ = y_Ga/x^V_Ga as the function of p_Ga, P_int, and the concentration of Ga atoms in initial Ga_1–xPb_x melts has been defined.

At the third step we have realized the results of the detail analysis of the quantitative composition of Ga_1–yPb_y binary layers in the improving of the one stage synthesis of ternary Pb_{1– z}Ga_zTe films. It has been found that the presence of tellurium vapor has increased in the degree of the deviation from thermodynamic equilibrium in HWE reaction chamber. The values of factor K₂ = z_Ga/x^V_Ga are higher than the values of K₁ in the most cases. On the basis of the general solution of the equations (2a) and (2b):

z*_Ga(p_Ga) = A₁ + B₁×p_Ga + C₁×p²_Ga                            (2a)

z*_Ga(P_int) = A₂ + B₂×P_int + C₂×P²_int                           (2b)

the improved conditions of ternary Pb_1–zGa_zTe films one stage synthesis have been designed. The comparison of the estimated z*_Ga and the real experimental results z_Ga concerning the concentration of Ga atoms in fabricated Pb_1–zGa_zTe films is presented in Table 1. It has been established that compositions of Pb_1–zGa_zTe samples synthesized by improved one stage method are characterized by the complete concurrence to expected z*_Ga values practically.

References:

1. M. Rahim, A Khiar, M. Fill, F. Felder, H. Zogg. Electron Lett. 18, 1037 (2011).
2. Lead Chalcogenides: Physics and Application. Ed. D. Khohlov. (Gordon & Breach, NY) 687 (2002)
3. A.M. Samoylov [et al]. Journ. Cryst. Growth. 38, 340 (2002).
4. S.V. Belenko [et al] Journ. Surface Investig. X-Ray, Synchrotron and Neutron Techn., 4, 170 (2010)
5. A.M. Samoylov [et al]. Russian Journ. General Chem. 81, 27 (2011)

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/29431 must be provided.

1. Heterostructures PbTe:Ga/BaF₂/CaF₂/Si for IR photodetectors
2. Surface morphology and structure of CaF₂/BaF₂–on-Si epitaxial layers and the electronic properties of the interface with the substrate
3. The Determination of Different Types of Conductivity Areas within Homogeneity Region of Ga Solid Solutions in PbTe films on Si-substrates 
4. The  determination  of solubility limits of gallium impurity  in  PbTe films doped with Ga  on  Si  substrates
5. electrical properties of lead telluride single crystals doped with bromine
6. The function of thiourea coordination compounds composition in synthesis of CdS thin films
7. The polymorphic modifications of CdS prepared from coordination compounds of thiourea
8. Synthesis of hydroxyapatite films
9. The charge states of In impurity atoms in PbTe<In>/Si films prepared by modified HWE technique
10. The determination of solubility limit of indium impurity in PbTe<In> thin films on Si substrates