DC-electric-field effect on CdSe nanocrystal embedded in Indium tin oxide film and its second-order nonlinearity

Abstract The effect of DC-electric-field on crystal-growth and second-order nonlinearity of CdSe nanocrystals embedded in amorphous indium tin oxide (ITO) films prepared by r.f. sputtering has been investigated. The current-voltage curves of the as-deposited films exhibit common characteristics; with raising voltage the current increases following the Ohmic law, and shows an abrupt decrease at around 36 V/cm. When samples were electrically-treated by applying a DC electric field of 50 V/cm, CdSe nanocrystals grew with the initial orientation kept unchanged as indicated by the X-ray diffraction patterns. Considering the fact that temperature of the sample surface was raised up to 250°C during the treatment, the crystal-growth occurred as a result of an increase in temperature due to the Joule heat. On the other hand, when the as-deposited films were heat-treated without applying voltage, CdSe crystallites grew with random orientations, accompanied by crystallization of ITO matrix at 400°C. From the difference in crystallization bahavior between the electrically- and heat-treated films, we infer that the preferential crystal-growth of CdSe in the electrically-treated film can be attributed to the electric field as well as the Joule heat. The second-harmonic intensity for the electrically-treated films was enhanced by two orders of magnitude compared with the as-deposited films and was twice as large as that of the heat-treated samples.