Second-Harmonic Generation in Oriented CdSe-Nanocrystal-Doped Indium Tin Oxide Film and its Application to an Infrared D
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ABSTRACT Second-harmonic generation in CdSe nanocrystals doped in indium tin oxide ( ITO films has been examined. The thin film samples were prepared by r.f. magnetron sputtering with ITO target on which CdSe chips were placed. The X-ray diffraction patterns of asdeposited films indicate that CdSe crystallites are precipitated in an amorphous ITO matrix, and they are preferentially oriented in the direction of (111) plane of zinc blende structure or (002) plane of wurtzite structure. The mean diameter of CdSe crystallite was estimated to be 3-5 nm using Scherrer's equation. Moreover, the CdSe crystallites grew with keeping its initial orientation when a dc voltage of 50 V/cm was applied in the direction parallel to the film surface. The application of the electric field effectively enhanced the secondharmonic intensity by two orders of magnitude compared to that of the as-deposited films. The second-order nonlinear coefficient d(2 ) for the electrically-treated specimen calculated on a basis of a modified Maker fringe theory is d 31 = 3.0 x 10 pm/V at the wavelength of 1064 nm, which is comparable to d values reported for CdSe single crystal , d31 = 25 pm/V at 1054 nm and d3 3 = 76 pm/V at 1064 nm.
INTRODUCTION II-VI semiconductors have large second-order nonlinearity in infrared spectral region [1] and therefore high potential to infrared applications such as an infrared detector and a generator of visible second-harmonic light [2]. CdSe is one of the II-VI semiconductors investigated most extensively and also possesses a large second-order nonlinearity [3], although a low transmittance in visible spectral range restricts its optical application. Thus, CdSe-doped transparent materials are attractive because of simultaneous realization of large second-order nonlinearity and relatively high transmittance. In this work, second-harmonic generation (SHG) from CdSe-nanocrystal-doped ITO thin films has been examined. In order to enhance the second-harmonic generation, electrical treatment in which a dc voltage was applied in the direction parallel to the film surface was performed in addition to heat treatment. X-ray photoelectron ( XPS ) and X-ray diffraction (XRD) measurements were also carried out to characterize the composition and the crystallization behavior of the films thus obtained. The effect of the electrical treatment on the crystallization of CdSe and second-harmonic generation was investigated by comparing the electrically-treated film to the heat-treated one. The second-order nonlinear coefficient, d('), which stands for the ability to generate second-harmonic wave was obtained using a modified Maker fringe theory.
421 Mat. Res. Soc. Symp. Proc. Vol. 607 © 2000 Materials Research Society
EXPERIMENTAL PROCEDURE Film Preparation CdSe-embedded ITO films were prepared by a r.f. magnetron sputtering system (ULVAC, RFS-200) using an oxidized target with In 2 0 3 and Sn0 2 in a weight proportion of 9:1 on which CdSe chips with a diameter of 13 mm were placed. In order to study the effect of CdSe concentration
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