Surface morphology of cds thin films by vacuum evaporation deposition

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Surface morphology of cds thin films by vacuum evaporation deposition

  1. 1. International JournalElectronics and Communication Engineering & Technology (IJECET), International Journal of of Electronics and Communication ISSN 0976 – & Technology (IJECET)ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) IJECETEngineering6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep - Oct (2010), © IAEMEVolume 1, Number 1, Sep - Oct (2010), pp. 131-137© IAEME, http://www.iaeme.com/ijecet.html ©IAEME SURFACE MORPHOLOGY OF CDS THIN FILMS BY VACUUM EVAPORATION DEPOSITION D KATHIRVEL a*, N SURIYANARAYANAN b, S PRABAHAR c, S SRIKANTH c a* Department of Physics, Kalaignar Karunanidhi Institute of Technology, Coimbatore, India b Department of Physics, Government College of Technology, Coimbatore, India. c Department of Physics, Tamilnadu College of Engineering, Coimbatore, IndiaABSTRACT Cadmium Sulphide thin films have been deposited on to well cleaned glasssubstrate in a vacuum of 10-6 Torr. The thickness of the films has been determined byquartz crystal monitor method. The surface morphology studies are performed usingvarious techniques such as Scanning electron microscope (SEM) and Atomic forceMicroscope (AFM). SEM and AFM are the best tools to investigate the surfacesmoothness and to find the grain size of the particles. The grain size is calculated for allfilms of different thickness.Keywords: CdS, Structural Properties, X-ray diffraction, SEM and AFM. 1. INTRODUCTION The wide energy gap of CdS semiconductor is one of the most importantproperties leading to the great experimental interest in these materials. CdS is a suitablewindow layer for solar cells [1] and also finds applications as optical filters andmultilayer light emitting diodes [2-4], photo detectors, TFETs, gas sensors andtransparent conducting semiconductors for optoelectronic devices [3-5]. Various methodsare used to deposit CdS thin films [6-7]. Among the vacuum evaporation is an attractive,effective method and the application at enables the deposition of thin films of larger areawith good uniformity [8-9]. The properties of the CdS thin films are strongly depends onthe internal structure. The wide ranges of experimental methods are available for theevaluation of structure of materials with high accuracy and precision. The present studyreveals the variation of surface morphology of CdS thin films. 2. EXPERIMENTAL DETAILS The CdS powder of purity 99% was evaporated using Tungsten conical basket(200 amps) under the pressure of 2 x 10-5 Torr on to a pre cleaned glass substrate (3.25 x2.75 x 0.1 cm dimension). The pressure was obtained by diffusion pump backed by rotary 131
  2. 2. International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep - Oct (2010), © IAEMEpump in the coating unit and was measured using Pirani and Penning gauge. A constantrate of evaporation of the order of 1 Å / sec was maintained throughout the filmfabrication. A rotary device was employed to maintain uniformity in film thickness. Thethickness of the film was controlled and measured by Quartz crystal monitor and thethickness monitor in a flat circular plate approximately 0.05 inch (1.4cm) in diameter and0.011 inch (0.28 cm) thick. A substrate heater arrangement was employed to grow thethin film at different substrate temperature. The Copper – constant and thermocouple wasemployed to measure the temperature inside the champer. Scanning electron microscopyis a power full tool for investigating surface topology of material. It operates in avacuum, with a high energy beam (typically from 5 to 20eV) focused into a spot ofseveral tens of nanometers in diameter (or fraction of nanometers in modern high-resolution instruments). Another possible characteristic of SEM have high energyelectrons, since samples may be loose powders, fractures surfaces, polished sections butthey must be dry without excessive out gassing. The SEM analysis was carried out using"FEI Quanta 200". The surface morphology of the films is investigated by means ofscanning electron microscope (SEM) and atomic force microscopy (AFM). 3. RESULT AND DISCUSSION 3.1. SEM ANALYSIS OF CDS THIN FILMS Scanning electron microscopy is a convenient technique to study themicrostructure of thin films. Fig. 1, Fig. 2 and Fig. 3 show the SEM images of CdS thinfilms of different thicknesses. The SEM micrographs of different thickness are analyzedat a resolution of 20µm with 5000x magnification. The SEM micrographs of 880 Åthickness, the distributions of grains are not uniform throughout all the regions. But thefilms are without any void, pinhole or cracks and that they cover the substrates well. Weclearly observe the small nanosized grains engaged in a fibrous-like structure, whichclearly indicates the glassy nature along with amorphous phase of CdS thin films. Thegrains are found to be thickly packed, and inter grain spacing is reduced in the case offilm thickness 930 Å shown in Fig. 2. Fig. 1. X-ray diffractogram of CdS thin film of thickness 880 Å 132
  3. 3. International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep - Oct (2010), © IAEME Fig. 2. X-ray diffractogram of CdS thin film of thickness 930 Å Fig. 3. X-ray diffractogram of CdS thin film of thickness 2550 Å From the Fig. 3, the SEM of higher thickness of 2550 Å, such a difference mightbe due to the presence of some amorphous phase in the films along with theirpredominant crystalline phase. The surface morphological study also indicates that thedecrease in the Cd content improves the surface smoothness. 3.2. AFM ANALYSIS OF CDS THIN FILMS Fig. 4 & 5 shows the two dimensional and three dimensional AFM micrograph ofthe CdS thin films having thickness of 880 Å, 930 Å and 2550 Å. The scanning is doneover an area of 1µm x 1µm.The AFM images exposed the high uniformity of the filmswith round-shaped nano particles, and also shows the beta phase films which consists ofgrain size 40-180 nm. 133
  4. 4. International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep - Oct (2010), © IAEME (a) 880 Å (b) 930 Å 134
  5. 5. International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep - Oct (2010), © IAEME (c) 2550 Å Fig. 4. Two dimensional AFM micrographs of CdS thin film of thickness (a) 880 Å (b) 930 Å & (c) 2550 Å (a) 880 Å 135
  6. 6. International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep - Oct (2010), © IAEME (b) 930 Å (c) 2550 Å Fig. 5. Three dimensional AFM micrographs of CdS thin film of thickness (a) 880 Å (b) 930 Å & (c) 2550 Å The maximum size of the particle is calculated by Scheorer equation. Themaximum size and the root mean square of the roughness (rms) of the surface of CdSfilms of thickness 880 Å, 930 Å and 2550 Å are tabulated in Table 1. 136
  7. 7. International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep - Oct (2010), © IAEME Table 1. Variation of particle size with thickness.Sl. No. Film thickness (Å) Particle size (nm) Roughness of the surface (nm)1 880 57.20 12.502 930 60.45 13.123 2550 165.75 23.78 From the Table 1. reveals that, the particle size and roughness of the surface ofthe CdS thin films increases with increase in thickness. 4. CONCLUSIONS CdS thin films prepared from Vacuum Evaporation deposition are amorphousnature in lower thickness and polycrystalline nature and the SEM micrographs of lowerthickness, the distributions of grains are not uniform throughout all the regions and also,which clearly indicates the glassy nature along with amorphous phase of CdS thin films.The SEM of higher thickness of 2550 Å, such a difference might be due to the presenceof some amorphous phase in the films along with their predominant crystalline phase.The surface morphological studies show that the size of the particles increases withincrease in thickness of the films by means of AFM.ACKNOWLEDGEMENTS The author would like to acknowledge the assistance of each of the following: Dr.P. Rajasekaran, Prof. and Head of Physics Department, Kalaignar Karunanidhi Instituteof Technology, Coimbatore, India. Dr. K V. Kannan Nithin , Assistant Professor, KathirCollege of Engineering, Coimbatore, India.REFERENCES[1] J.Herrero, M.T.Gutierrez, C.Guillen, J.M.Dona, M.A.Martinez, A.M.Chaparro, R.Bayon, Thin Solid Films, 361, 28, (2000).[2] M.E.Calixto, P.J Sebastian, Solar Energy Materials and Solar Cells, 59, 65, (1999).[3] U.Pal, R.Silva-Gonzalez, G.Martinez-Montes, M.Gracia-Jimenez, M.A.Vidal, Sh.Torres, Thin Solid Films, 305, 345, (1997).[4] J.H. Schon, O.Schenker, B.Batlogg, Thin Solid Films, 385, 271, (2001).[5] J.Levinson, F.R.Shepherd, P.J.Scanlon, W.D.Westwood, G.Este, M.Rider, Journal of Applied Physics, 53, 1193, (1982).[6] Toshiya Hayashi, Takehiro Nishikura, Tatsuro Suzuki, Yoshinori Ema, Journal of Applied Physics, 64, 3542, (1988).[7] T.L.Chu, S.S.Chu, C.Ferekides, C.Q.Wu, J.Britt, C.Wang, Journal of Applied Physics, 70, 7608, (1991).[8] T.L.Chu, S.S. Chu, C. Ferekides, C.Q. Wu, J. Britt, C. Wang, J. Appl. Phys., 70, 608, (1991).[9] S. Mathew, P.S. Mukerjee, K.P. Vijayakumar, Thin Solid Films, 254, 278 (1995). 137

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