In the experiment

reflection spectra of ZnO films

which deposited on Si substrate

were measured.Then

the reflection spectra were used to determine the complex dielectric constant and complex refraction index of ZnO films according to Kramers-Kronig(K-K)relationship.There are two conditions for using K-K method.One is the reflection light from the sample must be perpendicular to the sample surface.Another one is that the reflection spectrum must be over full range of wavelength.Therefore

we designed a special mirror with a small hole in center of the mirror.The radiation beam emitted from the light source was reflected by this mirror

and perpendicularly irradiated the surface of the sample.Through the hole in center of the mirror

the reflection light from the sample surface was detected by a monochromator.The reflection spectrum measured in the experiment was limited in a certain wavelength range.In order to calculate the optical constants by using K-K relationship

we choose an appropriate extrapolation to get the reflectivity for all wavelength.Finally

we calculated the complex dielectric constant and complex reflected index of ZnO films.From the result

it can be seen that the index of ZnO films is almost a constant of 3.5 in the range of visible range

and a peak value(maximum)appears at the wavelength of 430 nm.In the short wavelength

the index of ZnO film decreases and fluctuates between 0.5 and 2.5.These data remain to be conformed

because we suggest that there is not any absorption peak in the short wavelength of the reflection spectra when we use the extrapolation to get full reflection spectra.This supposition must be evidenced by a further experiment.