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

The effect of DC-electric-field on crystal-growth and second-order nonlinea rity of CdSe nanocrystals embedded in amorphous indium till oxide (ITO) fil ms prepared by r.f. sputtering has been investigated. The current-voltage c urves of the as-deposited films exhibit common characteristics: with raisin g voltage the current increases following the Ohmic law, and shows an abrup t decrease at around 36 V/cm. When samples were electrically-treated by app lying a DC electric field of 50 V/cm, CdSe nanocrystals grew with the initi al orientation kept unchanged as indicated by the X-ray diffraction pattern s. Considering the fact that temperature of the sample surface was raised u p to 250 degreesC during the treatment, the crystal-growth occurred as a re sult 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, C dSe crystallites grew with random orientations, accompanied by crystallizat ion of ITO matrix at 400 degreesC. From the difference in crystallization b ahavior between the electrically- and heat-treated films, we infer that the preferential crystal-growth of CdSe in the electrically-treated film can b e attributed to the electric field as well as the Joule heat. The second-ha rmonic intensity for the electrically-treated films was enhanced by two ord ers of magnitude compared with the as-deposited films and was twice as larg e as that of the heat-treated samples. (C) 2001 Acta Materialia Inc. Publis hed by Elsevier Science Ltd. All rights reserved.