Phase Formation in Thin Films of Cu-InS Ternary System

In this paper we present the results of studies on the interaction of thin films of Cu-In-S, which is obtained by evaporation of individual components in the plane of condensation, consisting of fresh chips NaCl. Electron-diffraction analysis shows that the length of the regions forming binary compounds and ternary compounds of CuInS2 with simultaneous and sequential deposition of components is the same. Thus we can speak with certainty that the existence of thin film of tetragonal phase of ternary compound is present in CuInS2.


Introduction
A I -B III -C VI chemical group ternary compounds with a particular nano dimensional thin films of Cu-In-S system are promising materials to create photosensih surface barrier structures with big integral sensitivity used by changing solar energy to electric energy (Johan, 2010;Taunier, 2005;Hiroaki, 2005).This paper deals with the investigated results on study of thin film interaction in Cu-In-S system which detailed study allows the existence of various phases of Cu-S, In-S systems and ternary compound of CuInS 2 , compound in filmy state to be revealed.The first evidence for Cu-S and In-S system state diagrams being double cross-sections of Cu-In-S system is in (Djurle, 1958;Morimoto, 1962;Khansen, 1962;Zargarova, 1967) and (Hogg, 1968) respectively.By interaction between Cu and S there have been formed compounds which compositions could be in agreement with the formulae of Cu 2 S, Cu 1.8 S being known as chalcousite and dihenite according to existing minerals in nature.The phase of Cu 1.75 S composition being known as anilite has been established in (Morimoto, 1969).In given system intermediate phases established in (Cook, 1970) are in agreement with Cu 1.92 S and Cu x S formulae.By In-S system component interaction In 2 S, InS, In 6 S 7 , In 5 S 6 , In 4 S 5 , In 3 S 4 , In 2 S 3 , In 3 S 5 composition compounds (Khansen, 1962;Zargarova, 1967) and (Hogg, 1968) have been formed.

Experimental Procedure
The comprehensive researched deals with results studied of thin films of interaction of Cu-İn-S system, which shows the existence of various phases of Cu-S, In-S in the ternary system of compound CuInS 2 composition in the film state to be revealed.To produce samples with continuously changing composition and to prevent Cu and S oxidation, re evaporation of films is obtained during the process of subsequent thermal treatment in vacuum have been placed in carbon capsule.Individual components of Cu and S have been evaporated in vacuum by pressure of residual gases no more 10 -4 Pa from three sources.Limiting tungsten conical helix from which Cu and In have been evaporated are at distance of 150 mm from each other at a height of 80 mm above substrates being at room temperature.
In this paper we analyze the results of studies of phase formation processes in the films of the system Cu-In-S, obtained by simultaneous deposition and stratified components of the system.In the process of obtaining thin films were realized in all phases of a single loop in the vacuum system VUP -4.Phase analysis was performed using films formed on the ESA electronograph production brand EMR-102.In the vacuum system can be obtained films of dissimilar materials, semiconductor -metal, semiconductor-insulator interface, etc. with a certain ratio of components having different thicknesses.Structure and properties of thin films is largely determined by the conditions of condensation and compliance of its structure with the structure of the substrate.It should be noted that the degree of purity and nature of the substrate topography and the surface temperature and the degree of vacuum, the rate of evaporation, molecular beam angle of incidence to the substrate also affects the structure and properties of the resulting films.
It should be noted that the presence of contamination greatly affects the electrical properties of the films.In Terms of growth in the film changed, if contamination located on the substrate in the form of small isolated islets from each other.Depending on whether the binding energy between the higher content of the film and contamination of materials or material between the film and the substrate-film form, or on islands or on the exposed portion of the substrate.
Therefore, before spraying had to be done, cleaning the substrate thoroughly as well as protecting them from the appearance of oil films resulting from the penetration of fluids from the vapor and primary diffusion pumps.
There have been newly used made spalls on NaCl, KCl, LiF single crystals and amorphous polyamide celluloid as substrates.The third source from S is at a height of 90 mm from condensation plane between sources Cu and In.In this case on the condensation plane the layer of continuously changing content of components are formed: alloy in this case system includes from 0 up to 100% copper, from 100 up to 0% indium and from 100% sulphur in the center up to 0% on limiting points of condensation plane, consequently all compound of Cu-In-S system.

Results and Discussion
Electron diffraction analysis of the layer like this allows the phase composition of component ternary field to be determined.By electron diffraction patterns obtained from the films being in close proximity to the source Cu there has been established existence of several regions: region of primarily resulting phase of chalcocite Cu 2 S with rhombic cell periods a=1.1881 nanometers; b=2.7323 nanometers; c=1.3494 nanometers, SYS Ab2m (C 15 20 ), which undergoes phase transition and goes into hexagonal chalcocite with the periods a=0,389 nanometers; c=0,668 nanometers, SYS C6\mmc (Buerger, 1944); region of Cu 2-x S face-centered cubic phase with crystal lattice periods a=0.560 nanometers and Cu 7 S 4 composition phase with rhombic structure periods a=0.789 nanometers; b=0.784 nanometers; c=1.101 nanometers, SYS Pnma (D 16 2h ) (Morimoto, 1969); region of CuS hexagonal phase pure compound with lattice constants a=0,3794 nanometers; c=1.6332 nanometers, SYS P6 3 \mmc checking with the data given in (Djurle, 1958) and also their mixtures Cu 7 S 4 with CuS.
Further films of primarily resulting phase α-In 2 S 3 have been annealed at T 313-328K.Mentioned films undergo thermal treatment within T328K for short time 3-5 min.in order significant losses of S not to be taken place.These films go erreversibly into crystal β-modification with crystallographic constants a=1.074 nanometers, SYS Fd3m-0 7 h .Amorphous film thermal treatment with S=4πsinθ/λ = 25.32 nanometers -1 ; 34.52 nanometers -1 ; 58.27 nanometers -1 (Figure 1) obtained on the substrates spaced 50-55mm and 55-60mm apart from Cu and In evaporator centers, in the direction of the source S is exactly in the center of condensation plane that allows polycrystalline CuInS 2 (Figure 2) with tetragonal lattice periods a=0.552 nanometers; c=1.108 nanometers , SYS I42d (D 12 2b ) (Hahn, 1953) and ( Novoselova, 1979) to be revealed, respectively.

Figure 3 .
Figure 3. Diagram of phase distribution on condensation plane for Cu-In-S system