SEMICONDUCTOR MATERIALS

Influence of pH of spray solution on optoelectronic properties of cadmium oxide thin films

R. M. Hodlur and M. K. Rabinal

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 Corresponding author: M. K. Rabinal, E-mail: mkrabinal@yahoo.com

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Abstract: Highly conducting transparent cadmium oxide thin films were prepared by the conventional spray pyrolysis technique. The pH of the spray solution is varied by adding ammonia/hydrochloric acid. The effect of pH on the morphology, crystallinity and optoelectronic properties of these films is studied. The structural analysis showed all the films in the cubic phase. For the films with pH <7 (acidic condition), the preferred orientation is along the (111) direction and for those with pH >7 (alkaline condition), the preferred orientation is along the (200) direction. A lowest resistivity of 9.9 × 10-4 Ω · cm (with carrier concentration = 5.1 × 1020 cm-3, mobility = 12.4 cm2/(V· s)) is observed for pH ≈ 12. The resistivity is tuned almost by three orders of magnitude by controlling the bath pH with optical transmittance more than 70%. Thus, the electrical conductivity of CdO films could be easily tuned by simply varying the pH of the spray solution without compromising the optical transparency.

Key words: spray pyrolysispHcadmium oxidethin filmselectrical conductivity



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Fig. 1.  The X-ray diffraction pattern of CdO thin films prepared by varying the pH of the spray solution.

Fig. 2.  Scanning electron micrographs of cadmium oxide thin films prepared by spray pyrolysis (a) S1, (b) S3, (c) S5 and (d) S7.

Fig. 3.  (Color online) UV-vis absorption spectra of cadmium oxide thin films deposited on glass substrate.

Fig. 4.  Semi-logarithmic current-voltage curves of cadmium oxide thin films prepared by varying the pH of the spray solution.

Fig. 5.  (a) A graph of the resistivity of CdO films as a function of the pH of the spray solution. (b) Charge carrier concentration and mobility as a function of the pH of the spray solution. The solid lines that connect the data points are merely guides for the eyes. These values are estimated using Hall effect and electrical conductivity measurements.

Table 1.   The details of preparation conditions for CdO films are given above. The glass substrate temperature was maintained at 375 C for all the samples and the molarity of 0.04 M of cadmium acetate is chosen for the present work. The electrical parameters such as electrical resistivity, carrier concentration and mobility of CdO thin films are also mentioned below.

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    Received: 20 June 2014 Revised: Online: Published: 01 March 2015

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      R. M. Hodlur, M. K. Rabinal. Influence of pH of spray solution on optoelectronic properties of cadmium oxide thin films[J]. Journal of Semiconductors, 2015, 36(3): 033003. doi: 10.1088/1674-4926/36/3/033003 R. M. Hodlur, M. K. Rabinal. Influence of pH of spray solution on optoelectronic properties of cadmium oxide thin films[J]. J. Semicond., 2015, 36(3): 033003. doi: 10.1088/1674-4926/36/3/033003.Export: BibTex EndNote
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      R. M. Hodlur, M. K. Rabinal. Influence of pH of spray solution on optoelectronic properties of cadmium oxide thin films[J]. Journal of Semiconductors, 2015, 36(3): 033003. doi: 10.1088/1674-4926/36/3/033003

      R. M. Hodlur, M. K. Rabinal. Influence of pH of spray solution on optoelectronic properties of cadmium oxide thin films[J]. J. Semicond., 2015, 36(3): 033003. doi: 10.1088/1674-4926/36/3/033003.
      Export: BibTex EndNote

      Influence of pH of spray solution on optoelectronic properties of cadmium oxide thin films

      doi: 10.1088/1674-4926/36/3/033003
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      • Corresponding author: E-mail: mkrabinal@yahoo.com
      • Received Date: 2014-06-20
      • Accepted Date: 2014-10-20
      • Published Date: 2015-01-25

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