Structural, Optical, and Electrical Properties of Zn-Doped CdO Thin Films Fabricated by a Simplified Spray Pyrolysis Technique

doi:10.1007/s40195-014-0168-6

Abstract

Abstract:

Thin films of zinc-doped cadmium oxide with different Zn-doping levels (0, 2, 4, 6, and 8 at%) were deposited on glass substrates by employing an inexpensive, simplified spray technique using perfume atomizer at relatively low substrate temperature (375°C) compared with the conventional spray method. The effect of Zn doping on the structural, morphological, optical, and electrical properties of the films was investigated. XRD patterns revealed that all the films are polycrystalline in nature having cubic crystal structure with a preferential orientation along the (1 1 1) plane irrespective of Zn-doping level. Zn-doping level causes a slight shift in the (1 1 1) diffraction peak toward higher angle. The crystallite size of the films was found to be in the range of 28-37 nm. The band gap value increases with Zn doping and reaches a maximum of 2.65 eV for the film coated with 6 at% Zn doping and for further higher doping concentration it decreases. Electrical studies indicate that Zn doping causes a reduction in the resistivity of the films and a minimum resistivity of 15.69 Ω cm is observed for the film coated with 6 at% Zn.

Key words: Semiconductors, Thin films, Crystal structure, Optical properties, X-ray diffraction

K. Usharani, A. R. Balu. Structural, Optical, and Electrical Properties of Zn-Doped CdO Thin Films Fabricated by a Simplified Spray Pyrolysis Technique[J]. Acta Metallurgica Sinica (English Letters), 2015, 28(1): 64-71.

Figures/Tables 11

Fig. 1 XRD patterns of Zn-doped CdO thin films fabricated by the simplified spray pyrolysis technique

Fig. 2 Variations of f(h k l) for (1 1 1) and (2 0 0) planes as a function of zinc concentration

Fig. 3 Shift in (1 1 1) peak Bragg angle of Zn-doped CdO films

Table 1 Comparison of observed and standard d-spacing values of Zn-doped CdO thin films

(h k l)	d-standard^a (10^-1 nm)	d-observed (10^-1 nm)
		Zinc concentration (at%)
		0	2	4	6	8
(1 1 1)	2.7112	2.7116	2.7061	2.7045	2.7044	2.7038
(2 0 0)	2.3480	2.3488	2.3442	2.3421	2.3424	2.3414
(2 2 0)	1.6602	1.6615	1.6580	1.6570	1.6570	1.6565
(3 1 1)	1.4158	1.4163	1.4139	1.4130	1.4131	1.4126
(2 2 2)	1.3556	1.3567	1.3546	1.3534	1.3530	1.3526

Table 2 Structural parameters of undoped and Zn-doped CdO films

Concentration of zinc (at%)	Lattice parameter, a (10^-1 nm)	Crystallite size, D (nm)	Strain, ε (10^-3)	Dislocation density, δ (10¹⁵ lines/m²)	Number of crystallites, N (10¹⁶)
0	4.696	36.02	3.387	0.771	2.33
2	4.687	30.69	4.259	1.224	3.44
4	4.684	28.58	3.968	1.062	4.68
6	4.684	36.51	3.330	0.750	4.62
8	4.683	34.53	3.523	0.838	2.79

Fig. 4 SEM images of undoped and Zn-doped CdO films: a undoped, b 2 at% Zn, c 4 at% Zn, d 6 at% Zn, e 8 at% Zn

Fig. 5 EDAX spectra of undoped and Zn-doped CdO films: a undoped, b 2 at% Zn, c 4 at% Zn, d 6 at% Zn, e 8 at% Zn

Table 3 Results of quantitative elemental analysis of Zn-doped CdO thin films

Material	Element						O/(Cd + Zn) compositional ratio (atomic)
	wt%			at%
	Cd	Zn	O	Cd	Zn	O
Undoped CdO	89.40	0	10.60	54.56	0	45.44	0.83
CdO : 2% Zn	85.78	0.92	13.30	51.68	0.87	47.44	0.9
CdO : 4% Zn	87.01	1.96	9.47	50.72	1.96	38.78	0.74
CdO : 6% Zn	86.63	2.89	10.48	52.44	3.01	44.55	0.8
CdO : 8% Zn	87.26	2.51	10.23	53.38	2.64	43.98	0.79

Fig. 6 Variations of electrical resistivity and TCR and ZCO films with different Zn doping concentrations

Fig. 7 Transmittance spectra (inset variation of maximum transmittance) of CdO films doped with different Zn concentrations

Fig. 8 Sketch of (αhγ)2 against hγ (inset variation of E g with Zn-doping concentrations) of Zn-doped CdO films

References 34

[1]	Z. Zhao, D.L. Morel, C.S. Ferekides, Thin Solid Films 413, 203 (2002)
[2]	C.H. Champness, C.H. Chan, Sol. Energy Mater.Sol.Cells 37, 72 (1995)
[3]	R. Ferro, J.A. Rodriquez, Sol. Energy Mater.Sol.Cells 64, 363 (2000)
[4]	B. Saha, R. Thapa, K.K. Chattopadhyay,Solid State Commun. 145, 33(2008)
[5]	M. Yan, M. Lane, C.R. Kannewruf,R.P.H. Changa, Appl. Phys. Lett. 78, 2342(2001)
[6]	A.A. Dakhel,Opt. Mater. 31, 691(2009)
[7]	B. Saha, S. Das, K.K. Chattopadhyay, Sol. Energy Mater.Sol.Cells 91, 1692 (2007)
[8]	R.J. Deokate, S.M. Pawar, A.V. Moholkar, V.S. Sawant, C.A. Pawar, C.H. Bhosale, K.Y. Rajpure,Appl. Surf. Sci. 254, 2187(2008)
[9]	R.R. Salunkhe, C.D. Lokhande, Sens.Actuators,B 129, 345 (2008)
[10]	C.H. Bhosale, A.V. Kambale, A.V. Kokate, K.Y. Rajpure, Mater. Sci.Eng.B 122, 67 (2005)
[11]	R.K. Gupta, K. Ghosh, R. Patel, P.K. Kahol,Appl. Surf. Sci. 255, 2414(2008)
[12]	X. Liu, C. Li, S. Han, J. Han, C. Zhou,Appl. Phys. Lett. 82, 1950(2003)
[13]	L.R. Gutierrez, J.J.C. Romero, J.M.P. Tapia, E.B. Calva, J.C.M. Flores, M.O. Lopez, Mater. Lett. 60, 3866(2006)
[14]	A.A. Dakhel, J. AlloysCompd. 539, 26(2012)
[15]	K. Usharani, A.R. Balu, G. Shanmugavel, M. Suganya, V.S. Nagarethinam,Int. J. Sci. Res. Rev. 2(3), 53(2013)
[16]	JCPDS, International Centre for diffraction data, Card No.75-0594, 1997
[17]	C. Sravani, K.T. Ramakrishna Reddy, P. Jayarama Reddy, Mater. Lett. 15, 356(1993)
[18]	K. Tanaka, A. Kunioka, Y. Sakai,Jpn. J. Appl. Phys. 8, 681(1969)
[19]	D.J. Seo, J. Korean Phys.Soc. 45, 1575(2004)
[20]	Chitra Agashe,M.G. Takwale, B.R. Marathe, V.G. Bhide, Solar Energy Mater. 17, 99(1988)
[21]	V. Bilgin, S. Kose, F. Atay, I. Akyuz,Mater. Chem. Phys. 94, 103(2005)
[22]	S. Prabahar, M. Dhanam, J. Cryst.Growth285, 41 (2005)
[23]	W. Dong, C. Zhu,Opt. Mater. 22, 227(2003)
[24]	Q. Chang, C. Chang, X. Zhang, H. Ye, G. Shi, W. Zhang, Y. Wang, X. Xin, Y. Song,Opt. Commun. 274, 201(2007)
[25]	X. Liu, C. Li, S. Han, J. Han, C. Zhou. Appl.Phys. Lett. 82, 1950(2003)
[26]	A. Tadjarodi, M. Imani,Mater. Lett. 65, 1025(2011)
[27]	A. Tadjarodi, M. Imani, H. Kerdari, J. Nanostruct.Chem. 3, 1(2013)
[28]	H.X. Ren, X.J. Huang, O. Yarimaga, Y.K. Choi, N. Gu, J. Colloid,Interface Sci. 334, 103(2009)
[29]	F. Atay, V. Bilgin, I. Akyuz, S. Kose,Mater. Sci. Semicond. Proc. 6, 197(2003)
[30]	D.M. Carbaddeda-Galicia, R. Castanedo-Perez, O. Jimenez-Sandoval, S. Jimenez-Sandoval, G. Torres-Delgado, C.I. Zuniga-Romero, Thin Solid Films 371, 105 (2000)
[31]	T. Fukano, T. Motohiro,Sol. Energy Mater. Sol. Cell. 82, 567(2004)
[32]	A. Zaoui, M. Zaoui, S. Kacimi, A. Boukortt, B. Bouhafs,Mater. Chem. Phys. 120, 98(2010)
[33]	E. Burstein,Phys. Rev. 93, 632(1954)
[34]	T.S. Moss,Proc. Phys. Soc. Lond. 367, 775(1954)