Indium Tin Oxide, ITO, is the industry standard for transparent conductive coatings. As such, the common metrics for characterizing ITO performance are its transmission and conductivity/resistivity (or sheet resistance). In spite of its recurrent use in a broad range of technological applications, the performance of ITO itself is highly variable, depending on the method of deposition and chamber conditions, and a single well defined set of properties does not exist. This poses particular challenges for the incorporation of ITO in complex optical multilayer stacks while trying to maintain electronic performance. Complicating matters further, ITO suffers increased absorption losses in the NIR – making the ability to incorporate ITO into anti-reflective stacks crucial to optimizing overall optical performance when ITO is used in real world applications. In this work, we discuss the use of ITO in multilayer thin film stacks for applications from the visible to the NIR. In the NIR, we discuss methods to analyze and fine tune the film properties to account for, and minimize, losses due to absorption and to optimize the overall transmission of the multilayer stacks. The ability to obtain high transmission while maintaining good electrical properties, specifically low resistivity, is demonstrated. Trade-offs between transmission and conductivity with variation of process parameters are discussed in light of optimizing the performance of the final optical stack and not just with consideration to the ITO film itself.
Silicon rich silicon oxide thin films have been fabricated by electron cyclotron resonance plasma enhanced chemical vapor deposition. Following their deposition, these films were subjected to thermal anneals at temperatures up to 1100°C for times of up to 120 minutes. Annealing of the films causes a phase separation of the material to form Si precipitates, which nucleate to form Si nanocrystals, within an amorphous SiO2 matrix. The nucleation of the nanocrystals was analyzed as a function of the composition of the films, as determined by Rutherford backscattering and elastic recoil detection analysis experiments, and the annealing conditions. The bonding structure of the films was analyzed using Fourier transform infrared spectroscopy. Surface morphology, including analysis of the size and distribution of the nanocrystals, was determined through the use of atomic force microscopy. Spectroscopic ellipsometry, in the range from 600 to 1100 nm, was used to examine the effects of the formation of nanocrystals on the optical properties, i.e., index of refraction and extinction coefficient, of the films. Photoluminescence spectra were used to show that due to quantum confinement effects the nanocrystals
exhibit luminescence, making them a potential candidate for integrated photonic emitters.