Synthesis and Characterization of Pb(S, Se)Thin Films.

Studies on chemically deposited Pb(S,Se) thin films J. D. Chaudhari *, R. D. Chaudhari * *, Dr. R. H. Bari + Department of Physics, G. D. M. Arts, K. R. N. Commerce & M. D. Science College, Jamner. Pin – 424 206 Abstract : Thin films of Pb(S,Se) [lead sulfoselenide] have been prepared on glass substrate at 50°C by simple chemical bath deposition technique. The starting materials used for deposition were lead acetate, tri-sodium citrate, sodium sulphite and elemental selenium. Ammonium hydroxide solution was used to adjust pH of the bath.

In order to obtain good quality thin films, time, deposition temperature and pH of the solution were optimized and they are found to be 1 hour, 50°C and 10 respectively. Characterization included XRD and UV spectroscopy and electrical conductivity. The results are discussed and interpreted. Keywords: Pb(S,Se), thin film, chemical bath deposition technique. 1. Introduction: Semiconducting lead salt alloys PbxSn1-xSe, PbxSn1-xTe and PbSxSe 1-x have attracted substantial attentation in recent years for their use as IR detectors and tunable lasers (1-3) in the form of Schottky barriers (4) and multilayered structures (5).

Thin films of these compounds have usually been prepared by co-evaporation (6,7), hot wall epitaxy (8-10). However, some alloy thin films have been prepared from aqueous solutions, such as PbxCd1-xS (11), PbxHg1-xS(12). However no such method of depositing thin films of the lead salt alloy PbSxSe1-x has been reported so far. In the present investigation, chemical bath deposition technique for depositing thin films of PbSxSe1-x is reported together with their structural ,optical and electrical characterization. The chemical bath deposition technique is the simplest and capable of large area fabrication technique at low cost.

In this technique, wastage of material is minimum and there is no need to handle the poisonous gases like H2Se and H2S. 2. Experimental Procedure : The chemical bath deposition technique was used to deposit the films of lead sulfoselenide. The starting materials used were lead acetate, sodium sulphite, elemental selenium. Tri-sodium citrate was used as complexing agent. Ammonium hydroxide solution was used to adjust pH of the reaction mixture. All the chemicals used were of AR grade. Good quality films obtained for optimized time, temperature of deposition and pH of solution of 1hour, 50o C and 10 respectively.

The process involved the reaction of pb2+, S2- & Se2- ions in deionised water solution. Elemental selenium (99. 95%) was dissolved in an aqueous solution of sodium sulphite (pH > 9) at 90o C to form a partial unstable Na2SeSO3 compound by reflux method. In order to obtain the films lead acetate was mixed with trisodium citrate. To this solution, mixture of thiourea and sodium selenosulphite was added. The grown film was washed several times with deionized water. The synthesized film was annealed in air at 350o C for 15 minutes. Structural characterization of the film was carried out with X-ray diffractometer system using CuK? adiation with wavelength 1. 5418 Ao. The optical absorption study of the films was carried out using Hitachi U-2000 spectrophotometer. The electrical study of the films was carried out using four probe set up (model no. DFP-02) scientific equipment, Roorke. 3. Result: 3. 1 Structural analysis Fig 1. XRD pattern of the sample Figure1 shows the diffractogram of the sample scanned in the range of 20-80o. The XRD pattern reveals that Pb(S,Se) film is polycrystalline in nature. The planes (021),(003),(113)/(030),(220) corresponds to Pb(S,Se) (JCPDS file no. 80-1592). The peak (042) corresponds to PbSe. 311), (331) are the peaks corresponding to PbS. 3. 2. Optical studies: Fig. 2 Plot of optical absorbance versus wavelength ? (nm) Optical absorption studies of Pb(S,Se) film was carried out in the wavelength (? ) range of 300-1100 nm at room temperature. The variation of absorbance with the wavelength (? ) is shown in Figure 2. The band gap energy of the sample was calculated from the absorption edge of the spectra. The calculated band gap energy of Pb(S,Se) was found to be 1. 92 eV. 3. 3 Electrical studies Electrical conductivity of the Pb(S,Se) thin film was measured by using four-probe method in the temperature range of 308-423 K.

Figure 3 shows variation of logarithm of conductivity with an inverse of temperature. It is clear from Figure 3 that the conductivity increases with increase in temperature indicating the semiconducting nature of Pb(S,Se). 4. Conclusions: Thin film of lead sulfoselenide can be prepared by simple chemical bath deposition technique on to the glass substrate at low temperature. The XRD of the sample clearly indicates that the synthesized material is of Pb(S,Se) which is polycrystalline in nature. From electrical study it conclude that the synthesized material is semiconducting in nature. Acknowledgements

The authors are thankful to Head, Department of Physics and Dr. V. V. Bhaskar, Principal, G. D. M. Arts, K. R. N. Commerce and M. D. Science College, Jamner for providing laboratory facilities for this work. The authors are also thankful to Prof. P. P. Patil, Director, Dept. of Physical Sciences and Dr. J. V. Sali for characterization of the sample. References: 1 J. N. Zemel, Solid State Surf Sci. , 1 (1969) 291. 2 T. C. Harman and I. Melngailis, Appl. SolidState Sci. , 4 (1974) 1. 3 H. Prier, Appl. Phys. , 20 (1979) 189. 4 R. B. Schoolar, J. D. Jenson and G. M. Black, Appl. Phys. Lett. , 31 (1977) 536, 620. 5 R. B. Schoolar,J. D.

Jenson,G. M. Black S. Foti andA. C. Bouley,InfraredPhys. ,20(1980)271. 6 S. Fujita, H. Ozaki, T. Shiosaki and A. Kawabate, J. Vac. Soc. Jpn. , 20 (1977) 412. 7 A. Lopez-Otero, Thin Solid Films, 49(1978) 1. LETTERS L47 8 R. F. Bis, A. Rodolakis and J. N. Zemel, Rev. Sci. Instrum. , 36 (1965) 1626. 9 J. D. Jenson and R. B. Schoolar, J. Vac. Sci. Technol. , 13 (1976) 920. 10 M. Bleicher, H. D. Wurziuger, H. Mainer and H. Prier, J. Mater. Sci. , 12 (1977) 317. 11 B. B. Nayak, H. N. AcharyaandG. B. Mitra, Bull. Mater. Sci. ,3(1981)317. 12 N. C. Sharma, D. K. Pandya, H. K. Seghal and K. L. Chopra, Mater. Res. Bull. , 11 (1976) 1109. ********