ZnO薄膜光学常数测量

利用Kramers-Kronig方法(K-K方法)测量了ZnO薄膜的复介电常数和复折射率(折射率和消光系数)。为了满足K-K方法所要求的条件，光源发出的光束通过一个特殊设计的中间带孔的反射镜垂直投射到ZnO薄膜表面，在ZnO薄膜表面产生的反射光穿过反射镜中间的小孔进入单色仪，从而测量出正入射情况下ZnO薄膜的反射光谱。对有限波段下测量的数据经合理的外推后，得出全波段的薄膜反射谱，然后利用K-K方法计算出ZnO薄膜的复介电常数和复折射率。实验结果表明，氧化锌薄膜在可见光范围内的折射率近似为一常数3．5；在430nm附近出现折射率最大值，而在短波长范围所对应的折射率大大降低，其值在0．5—2．5之间起伏波动。

Optical Constants of ZnO Thin Films

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 ir- radiated the surface of the sample. Through the hole in center of the mirror, the reflection light from the sample sur- face 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 con- stant 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 experi- ment.