J. Semicond. > Volume 36 > Issue 3 > Article Number: 033003

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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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

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



References:

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[2]

Burbano M, Scanlon D O, Watson G W. Sources of conductivity and doping limits in CdO from hybrid density functional theory[J]. J Am Chem Soc, 2011, 133: 15065.

[3]

Zheng Biju, Hu Wen. Influence of substrate temperature on the structural and properties of In-doped CdO films prepared by PLD[J]. Journal of Semiconductors, 2013, 34(5): 053003.

[4]

Chen Z, Li W, Li R. Fabrication of highly transparent and conductive indium-tin oxide thin films with a high figure of merit via solution processing[J]. Langmuir, 2013, 29: 13836.

[5]

Minami T. New n-type transparent conducting oxides[J]. MRS Bulletin, 2000: 38.

[6]

Gupta R K, Ghosh K, Patel R. Influence of oxygen partial pressure on optoelectrical properties of aluminum-doped CdO thin films[J]. Appl Surf Sci, 2008, 254: 5868.

[7]

Badeker K. Of the electrical conductivity and the thermoelectric power of some heavy metal compounds[J]. Ann Phys, 1907, 327(4): 749.

[8]

Yang Y, Jin S, Medvedeva J E. CdO as the archetypical transparent conducting oxide systematics of dopant ionic radius and electronic structure effects on charge transport and band structure[J]. J Am Chem Soc, 2005, 127: 8796.

[9]

Bhosale C H, Kambale A V, Kokate A V. Structural, optical and electrical properties of chemically sprayed CdO thin films[J]. Mater Sci Eng B, 2005, 122: 67.

[10]

Jin S, Yang Y, Medvedeva J E. Dopant ion size and electronic structure effects on transparent conducting oxides Sc-doped CdO thin films grown by MOCVD[J]. J Am Chem Soc, 2004, 126: 13787.

[11]

Zheng B J, Lian J S, Zhao L. Optical and electrical properties of Sn-doped CdO thin films obtained by pulse laser deposition[J]. Vacuum, 2011, 85: 861.

[12]

Khan M K R, Rahman M A, Shahjahan M. Effect of Al-doping on optical and electrical properties of spray pyrolytic nano-crystalline CdO thin films[J]. Current Applied Physics, 2010, 10: 790.

[13]

Kumaravel R, Ramamurthi K, Krishnakumar V. Effect of indium doping in CdO thin films prepared by spray pyrolysis technique[J]. J Phys Chem Solids, 2010, 71: 1545.

[14]

Calnan S, Tiwari A N. High mobility transparent conducting oxides for thin film solar cells[J]. Thin Solid Films, 2010, 518-1839.

[15]

Kul M, Zor M, Senol Aybek A. Electrical and optical properties of fluorine-doped CdO films deposited by ultrasonic spray pyrolysis[J]. Solar Energy Materials & Solar Cells, 2007, 91: 882.

[16]

Yan M, Lane M, Kannewurf C R. Highly conductive epitaxial CdO thin films prepared by pulsed laser deposition[J]. Appl Phys Lett, 2001, 78: 2342.

[17]

Ali H M, Mohamed H A, Wakkad M M. Properties of transparent conducting oxides formed from CdO alloyed with In2O3[J]. Thin Solid Films, 2007, 515: 3024.

[18]

Deokate R J, Pawar S M, Moholkar A V. Spray deposition of highly transparent fluorine doped cadmium oxide thin films[J]. Appl Surf Sci, 2008, 254: 2187.

[19]

Zheng B J, Lian J S, Zhao L. Optical and electrical properties of In-doped CdO thin films fabricated by pulse laser deposition[J]. Appl Surf Sci, 2010, 256: 2910.

[20]

Sahin B, Gulen Y, Bayansal F. Structural and optical properties of Ba-doped CdO films prepared by SILAR method[J]. Superlattices and Microstructures, 2014, 65: 56.

[21]

Saha B, Thapa R, Chattopadhyay K K. Bandgap widening in highly conducting CdO thin film by Ti incorporation through radio frequency magnetron sputtering technique[J]. Solid State Commun, 2008, 145: 33.

[22]

Zhao Z, Morel D L, Ferekides C S. Electrical and optical properties of tin-doped CdO films deposited by atmospheric metalorganic chemical vapor deposition[J]. Thin Solid Films, 2002, 413: 203.

[23]

Salunkhe R R, Dhawale D S, Gujar T P. Structural, electrical and optical studies of SILAR deposited cadmium oxide thin films: annealing effect[J]. Materials Research Bulletin, 2009, 44: 364.

[24]

Ramakrishna Reddy K T, Shanthini G M, Johnston D. Highly transparent and conducting CdO films grown by chemical spray pyrolysis[J]. Thin Solid Films, 2003, 427: 397.

[25]

Ferro R, Rodriguez J A, Vigil O. Chemical composition and electrical conduction mechanism for CdO:F thin films deposited by spray pyrolysis[J]. Mater Sci Eng B, 2001, 87: 83.

[26]

Uma Nerle, Hodlur R M, Rabinal M K. A sharp and visible range plasmonic in heavily doped metal oxide films[J]. Mater Res Express, 2014, 1: 015910.

[27]

Wang J T, Shi X L, Liu W W. Influence of preferred orientation on the electrical conductivity of fluorine-doped tin oxide films[J]. Sci Rep, 2014, 4: 3679.

[28]

Kumaravel R, Menaka S, Snega S R M. Electrical, optical and structural properties of aluminum doped cadmium oxide thin films prepared by spray pyrolysis technique[J]. Mater Chem Phys, 2010, 122: 444.

[29]

Maldonado A, Asomoza R, Canetas-Ortega J. Effect of the pH on the physical properties of ZnO:In thin films deposited by spray pyrolysis[J]. Solar Energy Materials & Solar Cells, 1999, 57: 331.

[30]

Sivakumar K, Senthil Kumar V, Muthukumarasamy N. Influence of pH on ZnO nanocrystalline thin films prepared by sol—gel dip coating method[J]. Bull Mater Sci, 2012, 35(3): 327.

[31]

Ravaro L P, Scalvi L. Influence of pH of colloidal suspension on the electrical conductivity of SnO2 thin films deposited via sol-gel-dip-coating[J]. Materials Research, 2011, 14: 113.

[32]

Rai P, Yu Y T. Potential barrier modulation in ZnO nanostructures and their CO sensing properties[J]. Anal Methods, 2013, 5: 4081.

[33]

Murthy L C S, Rao K S R K. Thickness dependent electrical properties of CdO thin films prepared by spray pyrolysis method[J]. Bull Mater Sci, 1999, 22: 953.

[34]

Gokul B, Matheswaran P, Sathyamoorthy R. Influence of annealing on physical properties of CdO thin films prepared by SILAR method[J]. J Mater Sci Technol, 2013, 29(1): 17.

[1]

Pasquarelli R M, Ginley D S, O'Hayre R. Solution processing of transparent conductors: from flask to film[J]. Chem Soc Rev, 2011, 40: 5406.

[2]

Burbano M, Scanlon D O, Watson G W. Sources of conductivity and doping limits in CdO from hybrid density functional theory[J]. J Am Chem Soc, 2011, 133: 15065.

[3]

Zheng Biju, Hu Wen. Influence of substrate temperature on the structural and properties of In-doped CdO films prepared by PLD[J]. Journal of Semiconductors, 2013, 34(5): 053003.

[4]

Chen Z, Li W, Li R. Fabrication of highly transparent and conductive indium-tin oxide thin films with a high figure of merit via solution processing[J]. Langmuir, 2013, 29: 13836.

[5]

Minami T. New n-type transparent conducting oxides[J]. MRS Bulletin, 2000: 38.

[6]

Gupta R K, Ghosh K, Patel R. Influence of oxygen partial pressure on optoelectrical properties of aluminum-doped CdO thin films[J]. Appl Surf Sci, 2008, 254: 5868.

[7]

Badeker K. Of the electrical conductivity and the thermoelectric power of some heavy metal compounds[J]. Ann Phys, 1907, 327(4): 749.

[8]

Yang Y, Jin S, Medvedeva J E. CdO as the archetypical transparent conducting oxide systematics of dopant ionic radius and electronic structure effects on charge transport and band structure[J]. J Am Chem Soc, 2005, 127: 8796.

[9]

Bhosale C H, Kambale A V, Kokate A V. Structural, optical and electrical properties of chemically sprayed CdO thin films[J]. Mater Sci Eng B, 2005, 122: 67.

[10]

Jin S, Yang Y, Medvedeva J E. Dopant ion size and electronic structure effects on transparent conducting oxides Sc-doped CdO thin films grown by MOCVD[J]. J Am Chem Soc, 2004, 126: 13787.

[11]

Zheng B J, Lian J S, Zhao L. Optical and electrical properties of Sn-doped CdO thin films obtained by pulse laser deposition[J]. Vacuum, 2011, 85: 861.

[12]

Khan M K R, Rahman M A, Shahjahan M. Effect of Al-doping on optical and electrical properties of spray pyrolytic nano-crystalline CdO thin films[J]. Current Applied Physics, 2010, 10: 790.

[13]

Kumaravel R, Ramamurthi K, Krishnakumar V. Effect of indium doping in CdO thin films prepared by spray pyrolysis technique[J]. J Phys Chem Solids, 2010, 71: 1545.

[14]

Calnan S, Tiwari A N. High mobility transparent conducting oxides for thin film solar cells[J]. Thin Solid Films, 2010, 518-1839.

[15]

Kul M, Zor M, Senol Aybek A. Electrical and optical properties of fluorine-doped CdO films deposited by ultrasonic spray pyrolysis[J]. Solar Energy Materials & Solar Cells, 2007, 91: 882.

[16]

Yan M, Lane M, Kannewurf C R. Highly conductive epitaxial CdO thin films prepared by pulsed laser deposition[J]. Appl Phys Lett, 2001, 78: 2342.

[17]

Ali H M, Mohamed H A, Wakkad M M. Properties of transparent conducting oxides formed from CdO alloyed with In2O3[J]. Thin Solid Films, 2007, 515: 3024.

[18]

Deokate R J, Pawar S M, Moholkar A V. Spray deposition of highly transparent fluorine doped cadmium oxide thin films[J]. Appl Surf Sci, 2008, 254: 2187.

[19]

Zheng B J, Lian J S, Zhao L. Optical and electrical properties of In-doped CdO thin films fabricated by pulse laser deposition[J]. Appl Surf Sci, 2010, 256: 2910.

[20]

Sahin B, Gulen Y, Bayansal F. Structural and optical properties of Ba-doped CdO films prepared by SILAR method[J]. Superlattices and Microstructures, 2014, 65: 56.

[21]

Saha B, Thapa R, Chattopadhyay K K. Bandgap widening in highly conducting CdO thin film by Ti incorporation through radio frequency magnetron sputtering technique[J]. Solid State Commun, 2008, 145: 33.

[22]

Zhao Z, Morel D L, Ferekides C S. Electrical and optical properties of tin-doped CdO films deposited by atmospheric metalorganic chemical vapor deposition[J]. Thin Solid Films, 2002, 413: 203.

[23]

Salunkhe R R, Dhawale D S, Gujar T P. Structural, electrical and optical studies of SILAR deposited cadmium oxide thin films: annealing effect[J]. Materials Research Bulletin, 2009, 44: 364.

[24]

Ramakrishna Reddy K T, Shanthini G M, Johnston D. Highly transparent and conducting CdO films grown by chemical spray pyrolysis[J]. Thin Solid Films, 2003, 427: 397.

[25]

Ferro R, Rodriguez J A, Vigil O. Chemical composition and electrical conduction mechanism for CdO:F thin films deposited by spray pyrolysis[J]. Mater Sci Eng B, 2001, 87: 83.

[26]

Uma Nerle, Hodlur R M, Rabinal M K. A sharp and visible range plasmonic in heavily doped metal oxide films[J]. Mater Res Express, 2014, 1: 015910.

[27]

Wang J T, Shi X L, Liu W W. Influence of preferred orientation on the electrical conductivity of fluorine-doped tin oxide films[J]. Sci Rep, 2014, 4: 3679.

[28]

Kumaravel R, Menaka S, Snega S R M. Electrical, optical and structural properties of aluminum doped cadmium oxide thin films prepared by spray pyrolysis technique[J]. Mater Chem Phys, 2010, 122: 444.

[29]

Maldonado A, Asomoza R, Canetas-Ortega J. Effect of the pH on the physical properties of ZnO:In thin films deposited by spray pyrolysis[J]. Solar Energy Materials & Solar Cells, 1999, 57: 331.

[30]

Sivakumar K, Senthil Kumar V, Muthukumarasamy N. Influence of pH on ZnO nanocrystalline thin films prepared by sol—gel dip coating method[J]. Bull Mater Sci, 2012, 35(3): 327.

[31]

Ravaro L P, Scalvi L. Influence of pH of colloidal suspension on the electrical conductivity of SnO2 thin films deposited via sol-gel-dip-coating[J]. Materials Research, 2011, 14: 113.

[32]

Rai P, Yu Y T. Potential barrier modulation in ZnO nanostructures and their CO sensing properties[J]. Anal Methods, 2013, 5: 4081.

[33]

Murthy L C S, Rao K S R K. Thickness dependent electrical properties of CdO thin films prepared by spray pyrolysis method[J]. Bull Mater Sci, 1999, 22: 953.

[34]

Gokul B, Matheswaran P, Sathyamoorthy R. Influence of annealing on physical properties of CdO thin films prepared by SILAR method[J]. J Mater Sci Technol, 2013, 29(1): 17.

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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]. J. Semicond., 2015, 36(3): 033003. doi: 10.1088/1674-4926/36/3/033003.

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Manuscript received: 20 June 2014 Manuscript revised: Online: Published: 01 March 2015

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