ITO film stack engineering for low-loss silicon optical modulators

The Indium Tin Oxide (ITO) platform is one of the promising solutions for state-of-the-art integrated optical modulators towards low-loss silicon photonics applications. One of the key challenges on this way is to optimize ITO-based thin films stacks for electro-optic modulators with both high extinction ratio and low insertion loss. In this paper we demonstrate the e-beam evaporation technology of 20 nm-thick ITO films with low extinction coefficient of 0.14 (N-c = 3.7 center dot 10(20) cm(-3)) at 1550 nm wavelength and wide range of carrier concentrations (from 1 to 10 x 10(20) cm(-3)). We investigate ITO films with amorphous, heterogeneously crystalline, homogeneously crystalline with hidden coarse grains and pronounced coarsely crystalline structure to achieve the desired optical and electrical parameters. Here we report the mechanism of oxygen migration in ITO film crystallization based on observed morphological features under low-energy growth conditions. Finally, we experimentally compare the current-voltage and optical characteristics of three electro-optic active elements based on ITO film stacks and reach strong ITO dielectric permittivity variation induced by charge accumulation/depletion (Delta n = 0.199, Delta k = 0.240 at lambda = 1550 nm under +/- 16 V). Our simulations and experimental results demonstrate the unique potential to create integrated GHz-range electro-optical modulators with sub-dB losses.

Automated summary

This paper investigates the optimization of Indium Tin Oxide (ITO) thin films for integrated optical modulators. The authors demonstrate the fabrication of ITO films with high extinction ratio and low insertion loss using e-beam evaporation technology. Different crystalline structures of ITO films are studied, and the mechanism of oxygen migration in film crystallization is analyzed. Experimental results show the potential of ITO films for creating electro-optical modulators with sub-dB losses.