Franta Daniel, Nečas David, Ohlídal Ivan
Appl Opt. 2015 Nov 1;54(31):9108-19. doi: 10.1364/AO.54.009108.
A dispersion model capable of expressing the dielectric response of a broad class of optical materials in a wide spectral range from far IR to vacuum UV is described in detail. The application of this universal dispersion model to a specific material is demonstrated using the ellipsometric and spectrophotometric characterization of a hafnia film prepared by vacuum evaporation on silicon substrate. The characterization utilizes simultaneous processing of data from multiple techniques and instruments covering the wide spectral range and includes the characterization of roughness, nonuniformity, transition layer, and native oxide layer on the back of the substrate. It is shown how the combination of measurements in light reflected from both sides of the sample and transmitted light allows the separation of weak absorption in films and substrates. This approach is particularly useful in the IR region where the absorption structures in films and substrates often overlap and a prior measurement of the bare substrate may be otherwise necessary for precise separation. Individual phenomena that contribute to the dielectric response, i.e., interband electronic transitions, electronic excitations involving the localized states, and phonon absorption, are discussed in detail. A quantitative analysis of absorption on localized states, permitting the separation of transitions between localized states from transitions between localized and extended states, is utilized to obtain estimates of the density of localized states and film stoichiometry.
详细描述了一种色散模型，该模型能够在从远红外到真空紫外的宽光谱范围内表达一大类光学材料的介电响应。通过对在硅衬底上真空蒸发制备的氧化铪薄膜进行椭偏和分光光度表征，展示了这种通用色散模型在特定材料上的应用。该表征利用了来自覆盖宽光谱范围的多种技术和仪器的数据的同时处理，并且包括对衬底背面的粗糙度、不均匀性、过渡层和原生氧化层的表征。展示了如何通过对样品两侧反射光和透射光的测量相结合，实现薄膜和衬底中弱吸收的分离。这种方法在红外区域特别有用，因为在该区域薄膜和衬底中的吸收结构经常重叠，否则可能需要事先测量裸衬底才能精确分离。详细讨论了对介电响应有贡献的各个现象，即带间电子跃迁、涉及局域态的电子激发和声子吸收。利用对局域态上吸收的定量分析，将局域态之间的跃迁与局域态和扩展态之间的跃迁分离，从而获得局域态密度和薄膜化学计量比的估计值。
