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Optics Express

Optics Express

  • Editor: Micha
  • Vol. 13, Iss. 23 — Nov. 14, 2005
  • pp: 9211–9216
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Optical nonlinearity of ZnO microcrystallite enhanced by interfacial state

Y. B. Han, J. B. Han, S. Ding, D. J. Chen, and Q. Q. Wang  »View Author Affiliations


Optics Express, Vol. 13, Issue 23, pp. 9211-9216 (2005)
http://dx.doi.org/10.1364/OPEX.13.009211


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Abstract

A series of ZnO microcrystallite films deposited on quartz substrates were annealed at the temperature of 600~1050 °C. A well c-axis grown wurtzite ZnO film was obtained at the annealing temperature of 850 °C. For the samples annealed above this temperature, the empirical parameter E0 increased calculated from transmittance spectra, which indicated the changes of the interface of ZnO microcrystallite. Measured by Z-scans, the nonlinear absorption coefficient βeff increased from 1.2×102 cm/GW to 1.1×103 cm/GW when the annealing temperature rose from 950 °C to 1050 °C, mainly due to the interfacial state enhancement.

© 2005 Optical Society of America

1. Introduction

ZnO as a compound semi-conductor has draw considerable attention for its excellent piezoelectric and optical properties. It can be made for integrated acousto-optic devices and ultraviolet photonic devices [1

1 . W. D. Hunt , “ Isomorphic surface acoustic waves on multilayer structures ,” J. Appl. Phys. 89 , 3245 – 3249 ( 2001 ). [CrossRef]

, 2

2 . H. Cao , Y. G. Zhao , S. T. Ho , E. W. Seelig , Q. H. Wang , and R. P. H. Chang , “ Random Laser Action in Semiconductor Powder ,” Phys. Rev. Lett. 82 , 2278 – 2281 ( 1999 ). [CrossRef]

]. ZnO films grown on silicon [3

3 . J. G. Ma , Y. C. Liu , R. Mu , J. Y. Zhang , Y. M. Lu , D. Z. Shen , and X. W. Fan , “ Method of control of nitrogencontent in ZnO films: Structure and photoluminescence properties ,” J. Vac. Sci. Technol. B 22 , 94 – 98 ( 2004 ). [CrossRef]

, 4

4 . V. Srikant and D. R. Clarke , “ Optical absorption edge of ZnO thin films: the effect of substrate ,” J. Appl. Phys. 81 , 6357 – 6364 ( 1997 ). [CrossRef]

], sapphire [4–7

4 . V. Srikant and D. R. Clarke , “ Optical absorption edge of ZnO thin films: the effect of substrate ,” J. Appl. Phys. 81 , 6357 – 6364 ( 1997 ). [CrossRef]

], LiNbO3 [8

8 . C. L. Jia , K. M. Wang , X. L. Wang , X. J. Zhang , and F. Lu , “ Formation of c -axis oriented ZnO opticalwaveguides by radio-frequency magnetron sputtering ,” Opt. Express 13 , 5093 – 5099 ( 2005 ), http://www.opticsexpress.org/abstract. cfm?URI=OPEX-13-13-5093 . [CrossRef] [PubMed]

], GaAs [9

9 . M. K. Ryu , S. H. Lee , M. S. Jang , G. N. Panin , and T. W. Kang , “ Postgrowth annealing effect on structureand optical properties of ZnO films grown on GaAs substrates by the radio frequency magnetron sputtering technique ,” J. Appl. Phys. 92 , 154 – 158 ( 2002 ). [CrossRef]

] and quartz [10–12

10 . R. J. Hong , J. B. Huang , H. B. He , Z. X. Fan , and J. D. Shao , “ Influence of different post-treatments on the structure and optical properties of zinc oxide thin films ,” Appl. Surf. Sci. 242 , 346 – 352 ( 2005 ). [CrossRef]

] substrates have been studied and the electrics [13

13 . Y. W. Hong and J. H. Kim , “ The electrical properties of Mn3O4-doped ZnO ,” Ceram. Int. 30 , 1301 – 1306 ( 2004 ). [CrossRef]

], photoluminescence [3

3 . J. G. Ma , Y. C. Liu , R. Mu , J. Y. Zhang , Y. M. Lu , D. Z. Shen , and X. W. Fan , “ Method of control of nitrogencontent in ZnO films: Structure and photoluminescence properties ,” J. Vac. Sci. Technol. B 22 , 94 – 98 ( 2004 ). [CrossRef]

, 14

14 . Zhang , Q. P. Wang , and Z. Y. Xue , “ Photoluminescence of ZnO films excited with light of different wavelength ,” Appl. Surf. Sci. 207 , 20 – 25 ( 2003 ). [CrossRef]

], optical absorption [4

4 . V. Srikant and D. R. Clarke , “ Optical absorption edge of ZnO thin films: the effect of substrate ,” J. Appl. Phys. 81 , 6357 – 6364 ( 1997 ). [CrossRef]

, 7

7 . N. R. Aghamalyan , I. A. Gambaryan , E. K. Goulanian , R. K. Hovsepyan , R. B. Kostanyan , S. I. Petrosyam , E.S. Vardanyan , and A. F. Zerrouk , “ Influence of thermal annealing on optical and electrical properties of ZnO films prepared by electron beam evaporation ,” Semicond. Sci. Technol. 18 , 525 – 529 ( 2003 ). [CrossRef]

, 10

10 . R. J. Hong , J. B. Huang , H. B. He , Z. X. Fan , and J. D. Shao , “ Influence of different post-treatments on the structure and optical properties of zinc oxide thin films ,” Appl. Surf. Sci. 242 , 346 – 352 ( 2005 ). [CrossRef]

, 12

12 . V. Gupta and A. Mansingh , “ Influence of post-deposition annealing on the structural and optical properties of sputtered zinc oxide film ,” J. Appl. Phys. 80 , 1063 – 1073 ( 1996 ). [CrossRef]

] and optical nonlinearities [6

6 . W. L. Zhang , H. Wang , K. S. Wong , Z. K. Tang , G. K. L. Wong , and R. Jain , “ Third-order optical nonlinearityin ZnO microcrystallite thin films ,” Appl. Phys. Lett. 75 , 3321 – 3323 ( 1999 ). [CrossRef]

, 11

11 . J. H. Lin , Y. J. Chen , H. Y. Lin , and W. F. Hsieh , “ Two-photon resonance assisted huge nonlinear refraction and absorption in ZnO thin films ,” J. Appl. Phys. 97 , 033526 (1–6) ( 2005 ). [CrossRef]

, 15–17

15 . G. M. Jia , G. Z. Zhang , W. H. Xiang , and J. B. Ketterson , “ Measurement of the Third-order Nonlinear Optical Coefficient of ZnO Crystals by Using ICCD-Z-Scan ,” Chin. Phys. Lett. 21 , 1356 – 1358 ( 2004 ). [CrossRef]

] have been investigated. Laser ablation [4

4 . V. Srikant and D. R. Clarke , “ Optical absorption edge of ZnO thin films: the effect of substrate ,” J. Appl. Phys. 81 , 6357 – 6364 ( 1997 ). [CrossRef]

], laser deposition [11

11 . J. H. Lin , Y. J. Chen , H. Y. Lin , and W. F. Hsieh , “ Two-photon resonance assisted huge nonlinear refraction and absorption in ZnO thin films ,” J. Appl. Phys. 97 , 033526 (1–6) ( 2005 ). [CrossRef]

], electron beam evaporation [7

7 . N. R. Aghamalyan , I. A. Gambaryan , E. K. Goulanian , R. K. Hovsepyan , R. B. Kostanyan , S. I. Petrosyam , E.S. Vardanyan , and A. F. Zerrouk , “ Influence of thermal annealing on optical and electrical properties of ZnO films prepared by electron beam evaporation ,” Semicond. Sci. Technol. 18 , 525 – 529 ( 2003 ). [CrossRef]

], molecular-beam epitaxy [6

6 . W. L. Zhang , H. Wang , K. S. Wong , Z. K. Tang , G. K. L. Wong , and R. Jain , “ Third-order optical nonlinearityin ZnO microcrystallite thin films ,” Appl. Phys. Lett. 75 , 3321 – 3323 ( 1999 ). [CrossRef]

] and sputtering technique [3

3 . J. G. Ma , Y. C. Liu , R. Mu , J. Y. Zhang , Y. M. Lu , D. Z. Shen , and X. W. Fan , “ Method of control of nitrogencontent in ZnO films: Structure and photoluminescence properties ,” J. Vac. Sci. Technol. B 22 , 94 – 98 ( 2004 ). [CrossRef]

, 5

5 . I. Sayago , M. Aleixandre , A. Martinez , M. J. Fernandez , J. P. Santos , J. Gutierrez , I. Gracia , and M. C. Horrillo , “ Structure studies of Zinc oxide films grown by RF magnetron sputtering ,” Synth. Met. 148 , 37 – 41 ( 2005 ). [CrossRef]

, 9

9 . M. K. Ryu , S. H. Lee , M. S. Jang , G. N. Panin , and T. W. Kang , “ Postgrowth annealing effect on structureand optical properties of ZnO films grown on GaAs substrates by the radio frequency magnetron sputtering technique ,” J. Appl. Phys. 92 , 154 – 158 ( 2002 ). [CrossRef]

, 10

10 . R. J. Hong , J. B. Huang , H. B. He , Z. X. Fan , and J. D. Shao , “ Influence of different post-treatments on the structure and optical properties of zinc oxide thin films ,” Appl. Surf. Sci. 242 , 346 – 352 ( 2005 ). [CrossRef]

, 12

12 . V. Gupta and A. Mansingh , “ Influence of post-deposition annealing on the structural and optical properties of sputtered zinc oxide film ,” J. Appl. Phys. 80 , 1063 – 1073 ( 1996 ). [CrossRef]

] have been applied to prepare ZnO films. For sputtering technique, the substrate temperature [18

18 . S. S. Lin , J. L. Huang , and D. F. Lii , “ Effect of substrate temperature on the properties of Ti-doped ZnO films by simultaneous rf and dc magnetron sputtering ,” Mater. Chem. Phys. 90 , 22 – 30 ( 2005 ). [CrossRef]

], sputtering power [5

5 . I. Sayago , M. Aleixandre , A. Martinez , M. J. Fernandez , J. P. Santos , J. Gutierrez , I. Gracia , and M. C. Horrillo , “ Structure studies of Zinc oxide films grown by RF magnetron sputtering ,” Synth. Met. 148 , 37 – 41 ( 2005 ). [CrossRef]

, 19

19 . X. H. Yu , J. Ma , F. Ji , Y. H. Wang , X. J. Zhang , C. F. Cheng , and H. L. Ma , “ Effects of sputtering power on the properties of ZnO:Ga films deposited by r. f magnetron-sputtering at low temperature ,” J. Cryst. Growth 274 , 474 – 479 ( 2005 ). [CrossRef]

], oxygen partial pressure [5

5 . I. Sayago , M. Aleixandre , A. Martinez , M. J. Fernandez , J. P. Santos , J. Gutierrez , I. Gracia , and M. C. Horrillo , “ Structure studies of Zinc oxide films grown by RF magnetron sputtering ,” Synth. Met. 148 , 37 – 41 ( 2005 ). [CrossRef]

, 20

20 . R. J. Hong , H. J. Qi , J. B. Huang , H. B. He , Z. X. Fan , and J. D. Shao , “ Influence of oxygen partial pressure on the structure and photoluminescence of direct current reactive magnetron sputtering ZnO thin films ,” Thin Solid Films 473 , 58 – 62 ( 2005 ). [CrossRef]

] and post-treatments [10

10 . R. J. Hong , J. B. Huang , H. B. He , Z. X. Fan , and J. D. Shao , “ Influence of different post-treatments on the structure and optical properties of zinc oxide thin films ,” Appl. Surf. Sci. 242 , 346 – 352 ( 2005 ). [CrossRef]

, 12

12 . V. Gupta and A. Mansingh , “ Influence of post-deposition annealing on the structural and optical properties of sputtered zinc oxide film ,” J. Appl. Phys. 80 , 1063 – 1073 ( 1996 ). [CrossRef]

, 21

21 . Z. B. Fang , Z. J. Yan , Y. S. Tan , X. Q. Liu , and Y. Y. Wang , “ Influence of post-annealing treatment on the structure properties of ZnO films ,” Appl. Surf. Sci. 241 , 303 – 308 ( 2005 ). [CrossRef]

] may significantly influence the structure and optical properties of the films, however, the interfacial state effect of ZnO microcrystallite was seldom reported, since the electrical and the optical properties are strongly affected by the interface and the microstructure of the films. In this letter, we investigated the influences of the microcrystallite structure and interfacial state effect on the linear and nonlinear optical properties of the ZnO films on quartz substrates annealed at the temperature of 600~1050 °C.

2. Experimental

The ZnO microcrystallite films were deposited at room temperature by using radio frequency (r.f.) reactive sputtering technique with a zinc target (purity: 99.99%, radius: 50mm), the target-substrate distance was about 60 mm. The sputtering gas was the mixture of Ar and O2 with the partial pressure ratio of 5:1 and the sputtering pressure was about 3.5×10-2 Torr. The sputtering power was 150W. After deposition, the series of samples were annealed at the temperatures of 600 °C, 750 °C, 850 °C, 950 °C and 1050 °C, respectively. The samples were held at each temperature for an hour in air atmosphere and then cooled to room temperature slowly. The structure and the microcrystallite size of the films were investigated by X-ray diffraction (XRD), the transmittance spectra measurements were carried out using a UV-VIS-NIR spectrophotometer (Varian, Cary 5000), and the nonlinear absorption and refraction were investigated by using Z-scan technique at the wavelength of 790 nm, in which a femtosecond (fs) Ti: Sapphire laser (Mira 900, Coherent) with pulse duration of 150 fs and repetition rate of 76 MHz was employed.

3. Results and discussion

Figure 1 is the XRD patterns of the films annealed at the temperatures of A: 600 °C, B: 750 °C, C: 850 °C, D: 950 °C and E: 1050 °C, respectively. The highest peaks corresponding to (002) plane of wurtzite ZnO locate at the diffraction angle (2θ) of 34.37°~ 34.76° in each curve. For samples A, B, D and E, peaks of (100), (002), (101), (102), (103) and (110) planes of wurtzite ZnO are found, but for sample C, only peak of (002) plane at 34.46° is found, which indicates that the highest c-axis oriented wurtzite ZnO films is obtained. For samples D and E, peaks of (107) and (228) planes of tridymite are found, this can be explained that ZnO films turned to be thinner at some areas and silicon oxide turned from normal amorphous body to tridymite above the annealing temperature of 870 °C [22

22 . T. Hashimoto , H. Fujita , and H. Hase , “ Effects of atomic hydrogen and annealing temperatures on some radiation-induced phenomena in differently originated quartz ,” Radiat. Meas. 33 , 431 – 437 ( 2001 ). [CrossRef]

]. It also can be seen that the (002) peak of wurtzite ZnO does not rise but fall with the rise of annealed temperature above 850 °C, which indicates a structure change of the films, this will be discussed in the following text. The ZnO microcrystallite size increases from about 20nm to 50nm with the rise of the annealing temperature from 600 °C to 1050 °C calculated by using the Debye–Scherrer formula.

Fig. 1. XRD patterns of the samples annealed at different temperatures: A: 600°C, B: 750°C, C: 850°C, D: 950°C and E: 1050°C.

Figure 2(a) is the optical transmittance spectra of the as-deposited and annealed films. The samples annealed below 850°C exhibit a high transmittance (>75%) in visible region and show a sharp fundamental absorption edge at the wavelength about 380nm, but for samples annealed at 950 °C and 1050 °C, the transmittance gradually falls with the decreasing of the wavelength in the visible region and show relatively smaller gradient absorption edges.

The linear absorption coefficient α 0 near the band edge in the energy region of hν<Eg empirically follows the exponential law [4

4 . V. Srikant and D. R. Clarke , “ Optical absorption edge of ZnO thin films: the effect of substrate ,” J. Appl. Phys. 81 , 6357 – 6364 ( 1997 ). [CrossRef]

]:

α0(hν)=AE032exp(E0),
(1)

where E 0 is an empirical parameter, describing the width of the localized states in the band gap [4

4 . V. Srikant and D. R. Clarke , “ Optical absorption edge of ZnO thin films: the effect of substrate ,” J. Appl. Phys. 81 , 6357 – 6364 ( 1997 ). [CrossRef]

,7

7 . N. R. Aghamalyan , I. A. Gambaryan , E. K. Goulanian , R. K. Hovsepyan , R. B. Kostanyan , S. I. Petrosyam , E.S. Vardanyan , and A. F. Zerrouk , “ Influence of thermal annealing on optical and electrical properties of ZnO films prepared by electron beam evaporation ,” Semicond. Sci. Technol. 18 , 525 – 529 ( 2003 ). [CrossRef]

], the value of E 0 can be calculated by [23

23 . F. Yakuphanoglu , M. Sekerci , and O. F. Ozturk , “ The determination of the optical constant of Cu(ll) compound having 1-chloro-2, 3- o -cyclohexylidinepropane thin film ,” Opt. Commun. 239 , 275 – 280 ( 2004 ). [CrossRef]

]:

E0=[dln(α0)dln(hν)]1
(2)

The interference fringes caused by the multi-reflection between two interfaces of the monolayer ZnO film with high refractive index are found in the visible region for the samples as-grown and 750 °C annealed. When the annealing temperature is above 950 °C, the interference fringes become weaker and disappear since the ZnO microcrystallites are melted into the quartz substrate. This also can be deduced from the XRD patterns of the samples annealed at 950 °C and 1050 °C, the peaks of tridymite appear and the intensity of wurtzite ZnO (002) peak decreases, which indicates the disorder orientation of ZnO microcrystallites and the crystallization of silicon oxide, these induce the fusing of ZnO film and the tridymite substrate at the interface. Similar phenomenon has been discovered for ZnO films grown on GaAs [9

9 . M. K. Ryu , S. H. Lee , M. S. Jang , G. N. Panin , and T. W. Kang , “ Postgrowth annealing effect on structureand optical properties of ZnO films grown on GaAs substrates by the radio frequency magnetron sputtering technique ,” J. Appl. Phys. 92 , 154 – 158 ( 2002 ). [CrossRef]

] and silicon substrate [24

24 . X. L. Xu , C. X. Guo , Z. M. Qi , H. T. Liu , J. Xu , C. S. Shi , C. Chong , W. H. Huang , Y. J. Zhou , and C. M. Xu , “ Annealing effect for surface morphology and luminescence of ZnO film on silicon ,” Chem. Phys. Lett. 364 , 57 – 63 ( 2002 ). [CrossRef]

].

The band gap energy (Eg) can be calculated from Fig. 2(b), which are the plot of (α 0 E phot)2 versus E phot for direct transition [4

4 . V. Srikant and D. R. Clarke , “ Optical absorption edge of ZnO thin films: the effect of substrate ,” J. Appl. Phys. 81 , 6357 – 6364 ( 1997 ). [CrossRef]

, 7

7 . N. R. Aghamalyan , I. A. Gambaryan , E. K. Goulanian , R. K. Hovsepyan , R. B. Kostanyan , S. I. Petrosyam , E.S. Vardanyan , and A. F. Zerrouk , “ Influence of thermal annealing on optical and electrical properties of ZnO films prepared by electron beam evaporation ,” Semicond. Sci. Technol. 18 , 525 – 529 ( 2003 ). [CrossRef]

], the values of Eg are obtained by extrapolating the linear parts of the curve to the energy axis (at α 0=0) [25

25 . K. M. Reddy , S. V. Manorama , and A. R. Reddy , “ Bandgap studies on anatase titanium dioxide nanoparticles ,” Mater. Chem. Phys. 78 , 239 – 245 ( 2002 ). [CrossRef]

]. For the as-grown film, the band gap energy is 3.42 eV, a little larger than that of the reported films prepared with other methods [4

4 . V. Srikant and D. R. Clarke , “ Optical absorption edge of ZnO thin films: the effect of substrate ,” J. Appl. Phys. 81 , 6357 – 6364 ( 1997 ). [CrossRef]

, 7

7 . N. R. Aghamalyan , I. A. Gambaryan , E. K. Goulanian , R. K. Hovsepyan , R. B. Kostanyan , S. I. Petrosyam , E.S. Vardanyan , and A. F. Zerrouk , “ Influence of thermal annealing on optical and electrical properties of ZnO films prepared by electron beam evaporation ,” Semicond. Sci. Technol. 18 , 525 – 529 ( 2003 ). [CrossRef]

], mainly results from the lack of oxygen in the deposition process. For the annealed films, a red-shift of the absorption edge compared to that of the as-grown one is found, which is mainly due to a weaker quantum confinement effect of the ZnO mircocrystalline induced by the increasing of the ZnO grain size. As shown in Fig. 2(c), the band gap energy decreases with the increase of ZnO microcrystallite size, similar curves have been simulated in ref [26

26 . M. Chakrabarti , S. Dutta , S. Chattapadhyay , A. Sarkar , D. Sanyal , and A. Chakrabarti , “ Grain size dependence of optical properties and positron annihilation parameters in Bi 2 O 3 powder ,” Nanotechnology 15 , 1792 – 1796 ( 2004 ). [CrossRef]

]. With the decrease of the band gap, the two-photon absorption (TPA) becomes possible [11

11 . J. H. Lin , Y. J. Chen , H. Y. Lin , and W. F. Hsieh , “ Two-photon resonance assisted huge nonlinear refraction and absorption in ZnO thin films ,” J. Appl. Phys. 97 , 033526 (1–6) ( 2005 ). [CrossRef]

].

Fig. 2. (a) Optical transmittance spectra of the series of samples. (b) Plot of (α 0 E phot)2 versus E phot for direct transition, band gap energy Eg are obtained by extrapolation to α 0=0. (c) Band gap energy Eg versus particle size. (d) The variation of E 0 with annealing temperature.

The E 0 value of the samples versus the annealing temperatures is shown in Fig. 2(d). The sharpest absorption edge corresponding to the minimum of E0 is observed for the samples annealed at 850 °C, which indicates a best stoichiometry of ZnO films [7

7 . N. R. Aghamalyan , I. A. Gambaryan , E. K. Goulanian , R. K. Hovsepyan , R. B. Kostanyan , S. I. Petrosyam , E.S. Vardanyan , and A. F. Zerrouk , “ Influence of thermal annealing on optical and electrical properties of ZnO films prepared by electron beam evaporation ,” Semicond. Sci. Technol. 18 , 525 – 529 ( 2003 ). [CrossRef]

], for samples annealed at 950 °C and 1050 °C, the E 0 value is larger than that of sample annealed at 850 °C. This is mainly due to the interdiffusion of zinc oxide microcrystallite and tridymite substrates. Zn diffuses into SiO2 crystal and Si into ZnO films, which enhance the effect of defect, thus the E 0 value increases.

The nonlinear absorption in the sample can be accounted for by an effective nonlinear absorption coefficient as β eff, which includes all nonlinear absorption such as saturated and reversed saturated absorption [27

27 . S. Couris , E. Koudoumas , A. A. Rutht , and S. Leach , “ Concentration and wavelength dependence of the effective third-order susceptibility and optical limiting of C 60 in toluene solution ,” J. Phys. B: At. Mol. Opt. Phys. 28 , 4537 – 4554 ( 1995 ). [CrossRef]

]. The nonlinear absorption is expressed by α=α 0+β eff I, where α 0 is the linear absorption coefficient of the film and I is the intensity of the laser. The third-order nonlinear absorption and refraction are investigated by Z-scan techniques. The open-and closed-aperture Z-scan curves are theoretical fitted by [28

28 . M. Sheik-Bahae , D. J. Hagan , and E. W. Ban Stryland , “ Dispersion and band-gap scaling of the electronic Kerr effect in solids associated with two-photon absorption ,” Phys. Rev. Lett., 65 , 96 – 99 ( 1990 ). [CrossRef]

]:

T=m=0(q0)m(1+z2z02)m(1+m)32(m0)
(3)
T=1+4Δϕ0(zz0)[(zz0)2+9][(zz0)2+1]
(4)

where T is the normalized transmittance and z is the distance along the lens axis in the far field. The nonlinear absorption coefficient β eff can be obtained by q 0=β eff I 0 L eff, where I 0 is the intensity of the laser beam at the focus (z=0), and L eff is the effective thickness of the film, which can be calculated from the thickness L≈690nm of the sample and the absorption coefficient α by L eff = [1-exp(-α 0 L)]/α 0. The nonlinear refractive index Δn/I 0 is calculated by ΔΦ 0=kΔnL eff, where k (k = 2πλ) is the wave vector of the incident laser.

Figure 3(a) is the open-aperture Z-scan trace of the sample annealed at 1050 °C. The valley configuration indicates a positive nonlinear absorption. The β eff value is calculated to be 1.1×103 cm/GW by fitting the experiment data with equation (3

3 . J. G. Ma , Y. C. Liu , R. Mu , J. Y. Zhang , Y. M. Lu , D. Z. Shen , and X. W. Fan , “ Method of control of nitrogencontent in ZnO films: Structure and photoluminescence properties ,” J. Vac. Sci. Technol. B 22 , 94 – 98 ( 2004 ). [CrossRef]

).

Figure 3(b) shows the value of β eff and α 0 as a function of annealing temperatures. For the samples annealed below 950 °C, the absolute value of β eff does not change significantly, but for ones annealed above 950 °C, the β eff value increases rapidly with the increase of the annealing temperature. A negative β eff value due to the saturated absorption of the defect states is measured in ref [11

11 . J. H. Lin , Y. J. Chen , H. Y. Lin , and W. F. Hsieh , “ Two-photon resonance assisted huge nonlinear refraction and absorption in ZnO thin films ,” J. Appl. Phys. 97 , 033526 (1–6) ( 2005 ). [CrossRef]

], which is similar to that of ours annealed at 750 °C. For samples annealed at 850 °C, there is a better stoichiometry of ZnO films from the above discussions, so the influence of the defect states is weaker and the β eff value changes to be positive due to reversed saturated absorption that induced by TPA [11

11 . J. H. Lin , Y. J. Chen , H. Y. Lin , and W. F. Hsieh , “ Two-photon resonance assisted huge nonlinear refraction and absorption in ZnO thin films ,” J. Appl. Phys. 97 , 033526 (1–6) ( 2005 ). [CrossRef]

]. For samples annealed at higher temperatures, the positive β eff value increases rapidly. The E 0 value increases because of the interdiffusion of the SiO2 substrates and ZnO films, which indicates a broadening of width of the localized states, so the transitions increase which enhance the β eff value. For samples annealed at 1050 °C, the β eff value is one order of magnitude larger than that at 950 °C due to the interfacial state enhancement. It can be seen in transmittance spectra that at 1050 °C no fringe is observed and the transmittance is the lowest among the five samples, which indicates more diffusion of ZnO microcrystallite into the silicon oxide and the increases of interface area of the microcrystallite. The decrease of transmittance with the increase of the annealing temperature (higher than 850 °C) in the visible and IR region is ascribed to the unusual interfacial state transition [29

29 . N. A. Dhas , A. Zaban , and A. Gedanken , “ Surface synthesis of zinc sulfide nanoparticles on silica microspheres: Sonochemical preparation, characterization, and optical properties ,” Chem. Mater. 11 , 806 – 813 ( 1999 ). [CrossRef]

].

It can be seen in XRD patterns that the Tridymite peaks in sample annealed at 1050 °C is higher than that in sample annealed at 950 °C, which indicates a better crystalline state of silicon oxide, and a wider area of thinner parts of ZnO layer, more ZnO microcrystallites disperse in tridymite lattice and the surfaces of ZnO microcrystallites are coated with silicon oxide, so the interface proportion of the ZnO microcrystallites with tridymite increases significantly. It is well known that the discontinuity of periodicity at the interface results in the difference between the energy band at the surface and that within the bulk. The electronic state limited in the interface area is usually located in the band gap of the bulk. In the nanoscale particles, the specific surface area is much larger than that in the bulk; therefore, the surface effect should be much stronger than that in the bulk [30

30 . G. T. Fei1 , S. H. Ma , Z. F. Ying , and L. D. Zhang , “ Third-order nonlinear optical properties and the influence of surface state of nanoscale Ag particles dispersed in silicon oil ,” Mater. Res. Bull. 34 , 217 – 224 ( 1999 ). [CrossRef]

]. Furthermore, as the ZnO microcrystallites are melted into the SiO2 substrate, the local field effect and the interband transition of electrons from the interfacial state to the unoccupied state near the Fermi level will greatly enhance the nonlinear absorption [30

30 . G. T. Fei1 , S. H. Ma , Z. F. Ying , and L. D. Zhang , “ Third-order nonlinear optical properties and the influence of surface state of nanoscale Ag particles dispersed in silicon oil ,” Mater. Res. Bull. 34 , 217 – 224 ( 1999 ). [CrossRef]

, 31

31 . R. G. Xie , J. Q. Zhuang , L. L. Wang , W. S. Yang , D. J. Wang , T. J. Li , and J. N. Yao , “ A WO 3 /ZnO nanoparticle composite system with high photochromic performance ,” Chem. J. Chinese U. 24 , 2086 – 2088 ( 2003 ).

]. Also for samples annealed at the temperature from 950 °C to 1050 °C, the nonlinear refractive index increase from 3.0×10-3 cm2/GW to 1.9×10-2 cm2/GW by fitting the experiment data with equation (4).

Fig. 3. (a) Open-aperture z-scan traces of the samples annealed at 1050°C, the solid line is the theoretical fit. (b) β eff and α 0 values versus annealing temperatures.

4. Conclusion

In summary, ZnO microcrystallite films were prepared on quartz substrates by r. f sputtering technique and annealed at different temperatures. XRD patterns and optical transmittance spectra demonstrated that the Tridymite and wurtzite ZnO fused together resulted from the interdiffusion of SiO2 substrates and ZnO microcrystallites at the interfaces for samples annealed at the temperatures above 950 °C. Measured by Z-scan technique, the nonlinear absorption coefficient increased from 1.2×102 cm/GW to 1.1×103 cm/GW with the increase of the annealing temperature from 950 °C to 1050 °C due to the interfacial state enhancement.

Acknowledgments

The authors express their thanks to Prof. Z. G. Zhou, J. Ding and W. Zhou for preparing the films and to X. Wang, H. M. Gong, S. D. Liu and S. Xiao for modification. This work was partially supported by National Natural Science Foundation of China (Grant No. 10474075).

References and links

1 .

W. D. Hunt , “ Isomorphic surface acoustic waves on multilayer structures ,” J. Appl. Phys. 89 , 3245 – 3249 ( 2001 ). [CrossRef]

2 .

H. Cao , Y. G. Zhao , S. T. Ho , E. W. Seelig , Q. H. Wang , and R. P. H. Chang , “ Random Laser Action in Semiconductor Powder ,” Phys. Rev. Lett. 82 , 2278 – 2281 ( 1999 ). [CrossRef]

3 .

J. G. Ma , Y. C. Liu , R. Mu , J. Y. Zhang , Y. M. Lu , D. Z. Shen , and X. W. Fan , “ Method of control of nitrogencontent in ZnO films: Structure and photoluminescence properties ,” J. Vac. Sci. Technol. B 22 , 94 – 98 ( 2004 ). [CrossRef]

4 .

V. Srikant and D. R. Clarke , “ Optical absorption edge of ZnO thin films: the effect of substrate ,” J. Appl. Phys. 81 , 6357 – 6364 ( 1997 ). [CrossRef]

5 .

I. Sayago , M. Aleixandre , A. Martinez , M. J. Fernandez , J. P. Santos , J. Gutierrez , I. Gracia , and M. C. Horrillo , “ Structure studies of Zinc oxide films grown by RF magnetron sputtering ,” Synth. Met. 148 , 37 – 41 ( 2005 ). [CrossRef]

6 .

W. L. Zhang , H. Wang , K. S. Wong , Z. K. Tang , G. K. L. Wong , and R. Jain , “ Third-order optical nonlinearityin ZnO microcrystallite thin films ,” Appl. Phys. Lett. 75 , 3321 – 3323 ( 1999 ). [CrossRef]

7 .

N. R. Aghamalyan , I. A. Gambaryan , E. K. Goulanian , R. K. Hovsepyan , R. B. Kostanyan , S. I. Petrosyam , E.S. Vardanyan , and A. F. Zerrouk , “ Influence of thermal annealing on optical and electrical properties of ZnO films prepared by electron beam evaporation ,” Semicond. Sci. Technol. 18 , 525 – 529 ( 2003 ). [CrossRef]

8 .

C. L. Jia , K. M. Wang , X. L. Wang , X. J. Zhang , and F. Lu , “ Formation of c -axis oriented ZnO opticalwaveguides by radio-frequency magnetron sputtering ,” Opt. Express 13 , 5093 – 5099 ( 2005 ), http://www.opticsexpress.org/abstract. cfm?URI=OPEX-13-13-5093 . [CrossRef] [PubMed]

9 .

M. K. Ryu , S. H. Lee , M. S. Jang , G. N. Panin , and T. W. Kang , “ Postgrowth annealing effect on structureand optical properties of ZnO films grown on GaAs substrates by the radio frequency magnetron sputtering technique ,” J. Appl. Phys. 92 , 154 – 158 ( 2002 ). [CrossRef]

10 .

R. J. Hong , J. B. Huang , H. B. He , Z. X. Fan , and J. D. Shao , “ Influence of different post-treatments on the structure and optical properties of zinc oxide thin films ,” Appl. Surf. Sci. 242 , 346 – 352 ( 2005 ). [CrossRef]

11 .

J. H. Lin , Y. J. Chen , H. Y. Lin , and W. F. Hsieh , “ Two-photon resonance assisted huge nonlinear refraction and absorption in ZnO thin films ,” J. Appl. Phys. 97 , 033526 (1–6) ( 2005 ). [CrossRef]

12 .

V. Gupta and A. Mansingh , “ Influence of post-deposition annealing on the structural and optical properties of sputtered zinc oxide film ,” J. Appl. Phys. 80 , 1063 – 1073 ( 1996 ). [CrossRef]

13 .

Y. W. Hong and J. H. Kim , “ The electrical properties of Mn3O4-doped ZnO ,” Ceram. Int. 30 , 1301 – 1306 ( 2004 ). [CrossRef]

14 .

Zhang , Q. P. Wang , and Z. Y. Xue , “ Photoluminescence of ZnO films excited with light of different wavelength ,” Appl. Surf. Sci. 207 , 20 – 25 ( 2003 ). [CrossRef]

15 .

G. M. Jia , G. Z. Zhang , W. H. Xiang , and J. B. Ketterson , “ Measurement of the Third-order Nonlinear Optical Coefficient of ZnO Crystals by Using ICCD-Z-Scan ,” Chin. Phys. Lett. 21 , 1356 – 1358 ( 2004 ). [CrossRef]

16 .

X. J. Zhang , W. Ji , and S. H. Tang , “ Determination of optical nonlinearities and carrier lifetime in ZnO ,” J. Opt. Soc. Am. B 14 , 1951 – 1955 ( 1997 ). [CrossRef]

17 .

X. Zhang , H. Fang , S. Tang , and W. Ji , “ Determination of two-photon-generated free-carrier lifetime in semiconductors by a single-beam Z-scan technique ,” Appl. Phys. B 65 , 549 – 554 ( 1997 ). [CrossRef]

18 .

S. S. Lin , J. L. Huang , and D. F. Lii , “ Effect of substrate temperature on the properties of Ti-doped ZnO films by simultaneous rf and dc magnetron sputtering ,” Mater. Chem. Phys. 90 , 22 – 30 ( 2005 ). [CrossRef]

19 .

X. H. Yu , J. Ma , F. Ji , Y. H. Wang , X. J. Zhang , C. F. Cheng , and H. L. Ma , “ Effects of sputtering power on the properties of ZnO:Ga films deposited by r. f magnetron-sputtering at low temperature ,” J. Cryst. Growth 274 , 474 – 479 ( 2005 ). [CrossRef]

20 .

R. J. Hong , H. J. Qi , J. B. Huang , H. B. He , Z. X. Fan , and J. D. Shao , “ Influence of oxygen partial pressure on the structure and photoluminescence of direct current reactive magnetron sputtering ZnO thin films ,” Thin Solid Films 473 , 58 – 62 ( 2005 ). [CrossRef]

21 .

Z. B. Fang , Z. J. Yan , Y. S. Tan , X. Q. Liu , and Y. Y. Wang , “ Influence of post-annealing treatment on the structure properties of ZnO films ,” Appl. Surf. Sci. 241 , 303 – 308 ( 2005 ). [CrossRef]

22 .

T. Hashimoto , H. Fujita , and H. Hase , “ Effects of atomic hydrogen and annealing temperatures on some radiation-induced phenomena in differently originated quartz ,” Radiat. Meas. 33 , 431 – 437 ( 2001 ). [CrossRef]

23 .

F. Yakuphanoglu , M. Sekerci , and O. F. Ozturk , “ The determination of the optical constant of Cu(ll) compound having 1-chloro-2, 3- o -cyclohexylidinepropane thin film ,” Opt. Commun. 239 , 275 – 280 ( 2004 ). [CrossRef]

24 .

X. L. Xu , C. X. Guo , Z. M. Qi , H. T. Liu , J. Xu , C. S. Shi , C. Chong , W. H. Huang , Y. J. Zhou , and C. M. Xu , “ Annealing effect for surface morphology and luminescence of ZnO film on silicon ,” Chem. Phys. Lett. 364 , 57 – 63 ( 2002 ). [CrossRef]

25 .

K. M. Reddy , S. V. Manorama , and A. R. Reddy , “ Bandgap studies on anatase titanium dioxide nanoparticles ,” Mater. Chem. Phys. 78 , 239 – 245 ( 2002 ). [CrossRef]

26 .

M. Chakrabarti , S. Dutta , S. Chattapadhyay , A. Sarkar , D. Sanyal , and A. Chakrabarti , “ Grain size dependence of optical properties and positron annihilation parameters in Bi 2 O 3 powder ,” Nanotechnology 15 , 1792 – 1796 ( 2004 ). [CrossRef]

27 .

S. Couris , E. Koudoumas , A. A. Rutht , and S. Leach , “ Concentration and wavelength dependence of the effective third-order susceptibility and optical limiting of C 60 in toluene solution ,” J. Phys. B: At. Mol. Opt. Phys. 28 , 4537 – 4554 ( 1995 ). [CrossRef]

28 .

M. Sheik-Bahae , D. J. Hagan , and E. W. Ban Stryland , “ Dispersion and band-gap scaling of the electronic Kerr effect in solids associated with two-photon absorption ,” Phys. Rev. Lett., 65 , 96 – 99 ( 1990 ). [CrossRef]

29 .

N. A. Dhas , A. Zaban , and A. Gedanken , “ Surface synthesis of zinc sulfide nanoparticles on silica microspheres: Sonochemical preparation, characterization, and optical properties ,” Chem. Mater. 11 , 806 – 813 ( 1999 ). [CrossRef]

30 .

G. T. Fei1 , S. H. Ma , Z. F. Ying , and L. D. Zhang , “ Third-order nonlinear optical properties and the influence of surface state of nanoscale Ag particles dispersed in silicon oil ,” Mater. Res. Bull. 34 , 217 – 224 ( 1999 ). [CrossRef]

31 .

R. G. Xie , J. Q. Zhuang , L. L. Wang , W. S. Yang , D. J. Wang , T. J. Li , and J. N. Yao , “ A WO 3 /ZnO nanoparticle composite system with high photochromic performance ,” Chem. J. Chinese U. 24 , 2086 – 2088 ( 2003 ).

OCIS Codes
(160.4330) Materials : Nonlinear optical materials
(190.3970) Nonlinear optics : Microparticle nonlinear optics
(240.4350) Optics at surfaces : Nonlinear optics at surfaces

ToC Category:
Research Papers

History
Original Manuscript: September 20, 2005
Revised Manuscript: October 27, 2005
Published: November 14, 2005

Citation
Y. B. Han, J. Han, S. Ding, D. Chen, and Q. Wang, "Optical nonlinearity of ZnO microcrystallite enhanced by interfacial state," Opt. Express 13, 9211-9216 (2005)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-13-23-9211


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References

  1. W. D. Hunt, �??Isomorphic surface acoustic waves on multilayer structures,�?? J. Appl. Phys. 89, 3245-3249 (2001). [CrossRef]
  2. H. Cao, Y. G. Zhao, S. T. Ho, E. W. Seelig, Q. H. Wang, and R. P. H. Chang, �??Random Laser Action in Semiconductor Powder,�?? Phys. Rev. Lett. 82, 2278-2281 (1999). [CrossRef]
  3. J. G. Ma, Y. C. Liu, R. Mu, J. Y. Zhang, Y. M. Lu, D. Z. Shen, and X. W. Fan, �??Method of control of nitrogen content in ZnO films: Structure and photoluminescence properties,�?? J. Vac. Sci. Technol. B 22, 94-98 (2004). [CrossRef]
  4. V. Srikant and D. R. Clarke, �??Optical absorption edge of ZnO thin films: the effect of substrate,�?? J. Appl. Phys. 81, 6357-6364 (1997). [CrossRef]
  5. I. Sayago, M. Aleixandre, A. Martinez, M. J. Fernandez, J. P. Santos, J. Gutierrez, I. Gracia and M. C. Horrillo, �??Structure studies of Zinc oxide films grown by RF magnetron sputtering,�?? Synth. Met. 148, 37-41 (2005). [CrossRef]
  6. W. L. Zhang, H. Wang, K. S. Wong, Z. K. Tang, G. K. L. Wong and R. Jain, �??Third-order optical nonlinearity in ZnO microcrystallite thin films,�?? Appl. Phys. Lett. 75, 3321-3323 (1999). [CrossRef]
  7. N. R. Aghamalyan, I. A. Gambaryan, E. K. Goulanian, R. K. Hovsepyan, R. B. Kostanyan, S. I. Petrosyam, E. S. Vardanyan and A. F. Zerrouk, �??Influence of thermal annealing on optical and electrical properties of ZnO films prepared by electron beam evaporation,�?? Semicond. Sci. Technol. 18, 525-529 (2003). [CrossRef]
  8. C. L. Jia, K. M. Wang, X. L. Wang, X. J. Zhang and F. Lu, �??Formation of c-axis oriented ZnO optical waveguides by radio-frequency magnetron sputtering,�?? Opt. Express 13, 5093-5099 (2005), <a href="http://www.opticsexpress.org/abstract.cfm?URI=OPEX-13-13-5093">http://www.opticsexpress.org/abstract.cfm?URI=OPEX-13-13-5093</a> [CrossRef] [PubMed]
  9. M. K. Ryu, S. H. Lee, and M. S. Jang, G. N. Panin and T. W. Kang, �??Postgrowth annealing effect on structure and optical properties of ZnO films grown on GaAs substrates by the radio frequency magnetron sputtering technique,�?? J. Appl. Phys. 92, 154-158 (2002). [CrossRef]
  10. R. J. Hong, J. B. Huang, H. B. He, Z. X. Fan, and J. D. Shao, �??Influence of different post-treatments on the structure and optical properties of zinc oxide thin films,�?? Appl. Surf. Sci. 242, 346-352 (2005). [CrossRef]
  11. J. H. Lin, Y. J. Chen, H. Y. Lin, and W. F. Hsieh, �??Two-photon resonance assisted huge nonlinear refraction and absorption in ZnO thin films,�?? J. Appl. Phys. 97, 033526(1-6) (2005). [CrossRef]
  12. V. Gupta and A. Mansingh, �??Influence of post-deposition annealing on the structural and optical properties of sputtered zinc oxide film,�?? J. Appl. Phys. 80, 1063-1073 (1996). [CrossRef]
  13. Y. W. Hong and J. H. Kim, �??The electrical properties of Mn3O4-doped ZnO,�?? Ceram. Int. 30, 1301-1306 (2004). [CrossRef]
  14. D. H. Zhang, Q. P. Wang and Z. Y. Xue, �??Photoluminescence of ZnO films excited with light of different wavelength,�?? Appl. Surf. Sci. 207, 20-25 (2003). [CrossRef]
  15. G. M. Jia, G. Z. Zhang, W. H. Xiang, J. B. Ketterson, �??Measurement of the Third-order Nonlinear Optical Coefficient of ZnO Crystals by Using ICCD-Z-Scan,�?? Chin. Phys. Lett. 21, 1356-1358 (2004). [CrossRef]
  16. X. J. Zhang, W. Ji and S. H. Tang, �??Determination of optical nonlinearities and carrier lifetime in ZnO,�?? J. Opt. Soc. Am. B 14, 1951-1955 (1997). [CrossRef]
  17. X. Zhang, H. Fang and S. Tang, W. Ji, �??Determination of two-photon-generated free-carrier lifetime in semiconductors by a single-beam Z-scan technique,�?? Appl. Phys. B 65, 549-554 (1997). [CrossRef]
  18. S. S. Lin, J. L. Huang and D. F. Lii, �??Effect of substrate temperature on the properties of Ti-doped ZnO films by simultaneous rf and dc magnetron sputtering,�?? Mater. Chem. Phys. 90, 22-30 (2005). [CrossRef]
  19. X. H. Yu, J. Ma, F. Ji, Y. H. Wang, X. J. Zhang, C. F. Cheng and H. L. Ma, �??Effects of sputtering power on the properties of ZnO:Ga films deposited by r. f. magnetron-sputtering at low temperature,�?? J. Cryst. Growth 274, 474-479 (2005). [CrossRef]
  20. R. J. Hong, H. J. Qi, J. B. Huang, H. B. He, Z. X. Fan, and J. D. Shao, �??Influence of oxygen partial pressure on the structure and photoluminescence of direct current reactive magnetron sputtering ZnO thin films,�?? Thin Solid Films 473, 58-62 (2005). [CrossRef]
  21. Z. B. Fang, Z. J. Yan, Y. S. Tan, X. Q. Liu, and Y. Y. Wang, �??Influence of post-annealing treatment on the structure properties of ZnO films,�?? Appl. Surf. Sci. 241, 303-308 (2005). [CrossRef]
  22. T. Hashimoto, H. Fujita, and H. Hase, �??Effects of atomic hydrogen and annealing temperatures on some radiation-induced phenomena in differently originated quartz,�?? Radiat. Meas. 33, 431-437 (2001). [CrossRef]
  23. F. Yakuphanoglu, M. Sekerci, and O. F. Ozturk, �??The determination of the optical constant of Cu(ll ) compound having 1-chloro-2, 3-o-cyclohexylidinepropane thin film,�?? Opt. Commun. 239, 275-280 (2004). [CrossRef]
  24. X. L. Xu, C. X. Guo, Z. M. Qi, H. T. Liu, J. Xu, C. S. Shi, C. Chong, W. H. Huang, Y. J. Zhou and C. M. Xu, �??Annealing effect for surface morphology and luminescence of ZnO film on silicon,�?? Chem. Phys. Lett. 364, 57-63 (2002). [CrossRef]
  25. K. M. Reddy, S. V. Manorama, A. R. Reddy, �??Bandgap studies on anatase titanium dioxide nanoparticles,�?? Mater. Chem. Phys. 78, 239-245 (2002). [CrossRef]
  26. M. Chakrabarti, S. Dutta, S. Chattapadhyay, A. Sarkar, D. Sanyal and A. Chakrabarti, �??Grain size dependence of optical properties and positron annihilation parameters in Bi2O3 powder,�?? Nanotechnology 15, 1792-1796 (2004). [CrossRef]
  27. S. Couris, E. Koudoumas, A. A. Rutht and S. Leach, �??Concentration and wavelength dependence of the effective third-order susceptibility and optical limiting of C60 in toluene solution,�?? J. Phys. B: At. Mol. Opt. Phys. 28, 4537-4554 (1995). [CrossRef]
  28. M. Sheik-Bahae, D. J. Hagan, and E. W. Ban Stryland, �??Dispersion and band-gap scaling of the electronic Kerr effect in solids associated with two-photon absorption,�?? Phys. Rev. Lett., 65, 96-99 (1990). [CrossRef]
  29. N. A. Dhas, A. Zaban, and A. Gedanken, �??Surface synthesis of zinc sulfide nanoparticles on silica microspheres: Sonochemical preparation, characterization, and optical properties,�?? Chem. Mater. 11, 806-813 (1999). [CrossRef]
  30. G. T. Fei1, S. H. Ma, Z. F. Ying and L. D. Zhang, �??Third-order nonlinear optical properties and the influence of surface state of nanoscale Ag particles dispersed in silicon oil,�?? Mater. Res. Bull. 34, 217-224 (1999). [CrossRef]
  31. R. G. Xie, J. Q. Zhuang, L. L. Wang, W. S. Yang, D. J. Wang, T. J. Li and J. N. Yao, �??A WO3/ZnO nanoparticle composite system with high photochromic performance,�?? Chem. J. Chinese U. 24, 2086-2088 (2003).

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