Chemical Bath Deposition and Study of Semiconductor Thin Films
in Cu2S−In2S3 System
Stanislav S. Tulenin a, Andrei V. Pozdun a, Konstantin A. Karpov a, Darya A. Novotorkina a, Michael S. Rogovoi a, Larisa N. Maskaeva a, Vyacheslav F. Markov a , *
a Ural Federal University named after the first President of Russia B.N. Yeltsin, Ekaterinburg, Russian Federation
* Corresponding author
E-mail addresses: (V.F. Markov)
In the first time thin films of InxCu1−xSyO1−y composition with the content of indium up to 9.63 at% were obtained by means of a chemical bath deposition from a system “indium chloride − copper chloride − sodium hydroxide − thiourea” and “indium chloride − copper chloride − sodium hydroxide – trilon B − thiourea”. The experimental date on the distribution and the atomic ration of elements in synthesized patterns obtained by the x-ray photoelectron spectroscopy were discussed. The change in the surface microstructure of thin films depending on the temperature and the composition of reaction bath were determined by means of scanning electron microscopy. The structure of obtained thin films has n-type of conductivity.
Keywords: copper sulfide (I), indium sulfide(III), thin films, solid solutions of replacement, x-ray photoelectron spectroscopy.
The people stands near to a new discover that connected with solution of difficult problems. As last decades a great force was direct to solution of removable energy problem. The scientific attention in any removable field direct to a new semiconductor material and this deposition method. The thin film chalcopyrite structures we can refer to promising material for solar cells.
The first representative in a line of chalcopyrite semiconductor is copper(I)-indium(III) disulfide Cu2S−In2S3. Collection of a properties such as high absorption factor of incident sunlight α (~10–5 см–1) (Jing-Jing et al., 2012), optimal energy band gap (1.5 eV) (Novoselova, 1979), rather high efficiency factor (~13%) (Fiechter, 2008), radiation stability (Maier et al., 2011), low industrial cost and environment safety in comparison with CdS is causing that these semiconductors use for solar cells preparation. Moreover a improvement of optical properties of chalcopyrite thin films Cu2S−In2S3 is caring out by means of control doping by elements such as Ga, Zn, Fe, Se doping (Yanfeng et al., 2011; Kuan-ting et al., 2013; Sharma et al., 2009).
There are different deposition methods for semiconductor material in a system Cu2S−In2S3. For example, it is high-speed magnetron spraying in a vacuum, spraying of water solutions with pyrolysis on heating a substrate (Lee, JunHo, 2010), physical deposition from gas phase, molecular-beam epitaxy (Chepra, Das, 1986), deposition by a sulfidization method on separate layers Cu-In (Merdes et al., 2011), electrochemical deposition (Jing-Jing et al., 2012) and chemical bath deposition (CBD) (Sharma et al., 2009; Yoon et al., 2012).
Attractiveness of CDB is not only its technology simplicity, the absence of deep vacuum or high temperature but also a deposition possibility for supersaturated solid solution, flexible control of a film properties that is vary difficult or impossible to achieve. As a result these factors are promising a low-temperature chemical deposition methods for copper(I)-indium(III) disulfide. However, literature data about complex physical and chemical studies for thin films of copper (I) and indium (III) sulfides and this replaced solid solution by CBD is absent.
Earlier we noticed from carried out thermodynamic researches (Fedorova et al., 2015; Maskaeva et al., 2012) that is a concentration region for copper (I) and indium (III) sulfides codeposition in two different system: hydroxide-system and trilonate-system. Also we showed that is a wide region of indium hydroxide steady which can impede a sulfide phase formation.
Purpose of the present work is carrying out of chemical bath co-deposition of thin films of copper (I) and indium sulfides and physical and chemical studies of their composition and microstructure.
2. Materials and methods
Deposition of Cu(I)−In−S thin films was carrying out on preliminary defatting sitall substrates (СТ-50-1 mark) from two different reaction mixture. The first of them contained indium chloride InCl3, copper chloride CuCl2, sodium hydroxide NaOH, thiourea N2H4CS. The second reaction mixture additionally contained trilon B Na2C10H14O8N2·2H2O. The NH2OH·HCl addition in reaction mixture had entered to transfer the copper Cu2+ in Cu+. The synthesis of thin films was carried out in a range of temperatures 333−353 K in glass leak proof reactors in which substrates fixed in specially made ftoroplaste device were placed. Reactors were located in thermostat TC-TB-10 with the accuracy of maintenance of temperature 00.1о. Deposition time 120 minutes was fixed for all thin films. Thickness of obtained simples has been measured on interferometer Linnik's MII-4M. Dark resistance measurements of semiconductor Cu(I)−In−S thin films has been measured on equipment К.54.410. Composition and main form of compounds in thin films were studied by means of X-ray photoelectron spectroscopy (XPS) method on ESCALAB MK II (VG Scientific, Great Britain) X-ray photoelectron spectrometer using magnesium cathode MgKα (1253.6 eV) as the non-monochromatized X-ray excitation source. The Cu2p5/2 line was calibration line with energy 932.5 eV. Scanning electron microscopy (SEM) of a simple surface was occurred on JEOL JSM-6390 LA instrument in second electron (SE) with JED 2300 tool for energy dispersive X-ray (EDX) analysis. Semiconductor type of obtained thin films was studied by means of a generated voltage measures.
3. Results and discussions
Concentration region and codeposition рН for copper (I) and indium sulfides was obtained by predicted calculation of CBD condition in Cu2S-In2S3system. For this aim analyses of ion balances in two complex systems was carried out (Maskaeva et al., 2012) that revealed which copper (I) and indium sulfides co-deposition is possible in wide pH region from 3.5 to 10, but in the case of trilon B is the only possible in a high alkaline condition.
Smooth Cu−In−S thin films with rather good adhesion to sitall substrate were deposited in experiment from carried out thermodynamic researches. Colour of thin films changes from light-brown (send-coloured) up to dark-brown with green shade.
The study of a main element forms and them composition in Cu−In−S thin films were carried out by means of XPS. For this survey spectra, region In3delectron core level of indium, region Cu2p electron core level of copper, region S2p electron core level of sulfur and region from 10 to 90 eV containing In4d and Cu3p peaks were recorded.
The XPS data showed that chalcopyrite thin film content indium from 4.05 to 9.63 at% with deposition condition and initial reagent concentrations (see table). The copper amount exceed indium and fluctuate from 25.76 to 49.43 at%, and sulfur is in deficiency (12.99−26.28 at%). High oxygen quantity, except for main elements, from 20.14 to 52.36 at% in studied films was obtained.
For the first time InxCu1−xSyO1−y thin films were deposited by means of CBD in InCl3 − CuCl2 − NaOH − N2H4CS and InCl3 − CuCl2 − Na2C10H14O8N2·2H2O − NaOH −N2H4CS systems at 333−353 K with thickness 115−570 nm and good adhesion to sitall substrate. XPS data showed that surface of thin film in Cu2S−In2S3 system include 4.05−9.63 at% of indium, 25.76−49.43 at% of copper, 12.99−26.28 at% of sulfur. Moreover, film composition is including metal oxide phases with 20.12−52.36 at% of oxygen which predicted from ion balance calculation. SEM showed that composition of reaction mixture and deposition temperature depends on morphology of InxCu1−xSyO1−y nanostructured films. The n-type conduction of InxCu1−xSyO1−y thin films was obtained. The dark resistance varies from 3 to 5 kОm on square meter for deposited films from trilonate-system and from 32 to 8 kОm on square meter for deposited films from second system.
The research was supported by the Russian Fund of Basis Research (№ 14-03-00121) and the Ministry of Education and Science of the Russian Federation in the framework of the governmental task № 4.1270.2014/K.
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