研究目的
To develop an algorithm for solving the inverse problem of multiangular spectrophotometry for a uniform film on a plane-parallel glass substrate of finite thickness, and to investigate the dispersive properties of pure and Al-doped ZnO films, including the effects of doping on the absorption band and refractive index.
研究成果
The developed algorithm successfully determined the thickness and spectral characteristics of ZnO and ZnO:Al films. Doping with Al shifts the absorption band to shorter wavelengths, decreases the refractive index, and increases light attenuation in the short-wavelength region. Films contain air pores (4% for ZnO, 7% for ZnO:Al), affecting optical properties. The approximations for absorption coefficient have limited accuracy, with Eq. 3 being the most reliable. Band gaps were found to be 3.18 eV for ZnO and 3.46 eV for ZnO:Al, with discrepancies due to film non-uniformities.
研究不足
The algorithm assumes a uniform film and does not account for non-uniformities such as pores in the surface layer, which can affect accuracy. The approximations used (e.g., Eqs. 2-5) have applicability limits, especially near absorption edges. The spectrophotometer cannot measure at zero incidence angle, and light path length increases with angle, requiring knowledge of refractive indices for accurate calculations.
1：Experimental Design and Method Selection:
The study involved developing an algorithm for multiangular spectrophotometry using s- and p-polarized waves to solve the inverse problem for a uniform film on a substrate. Two computer programs were developed: one integrating the monochromator Gaussian instrument function with coherent reflectances and transmittances, and another summing beam orders. Least-squares methods were used for numerical determination of optical characteristics.
2：Sample Selection and Data Sources:
Glass substrates were used, treated with an ion beam before deposition. ZnO and ZnO:Al films were deposited by magnetron HF sputtering of targets (Kurt J. Lesker Co., 2% Al in ZnO) in Ar at 1 Pa pressure. Sputtering times were 15 min for ZnO and 45 min for ZnO:Al.
3：List of Experimental Equipment and Materials:
Equipment includes an IKG-1 horizontal optimeter for substrate thickness measurement, a Photon RT spectrophotometer (Essent Optics, Belarus) for reflectance and transmittance measurements, and an ES2 ellipsometer (FGUP SKB, IRE, RAN, Russia) for ellipsometric measurements. Materials include glass substrates, ZnO and ZnO:Al2O3 targets.
4：Experimental Procedures and Operational Workflow:
Substrates were treated and films deposited. Spectral measurements were taken for TE- and TM-polarized waves at incidence angles of 8° and 40° in the range 300–950 nm. Ellipsometric measurements were at 65° incidence angle in 380–950 nm range. Data were processed using developed algorithms and standard software.
5：Data Analysis Methods:
Numerical reproduction of optical characteristics using least-squares methods, interpolation with Drude-Lorentz and Sellmeier formulas, and Tauc extrapolation for band gap determination.
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