The Effect of Carrier Distribution on Performance of ENZ-Based Electro-Absorption Modulator Behrang Hadian Siahkal-Mahalle 1 & Kambiz Abedi 1 Received: 26 January 2020 /Accepted: 5 May 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020 Abstract Recently, epsilon-near-zero (ENZ) has been emerging as an important field of research which is the study of light-matter interactions in the presence of materials with zero permittivity. Since in many scientific works the uniform model of carrier distribution of Indium tin oxide (ITO) has been utilized, we want to investigate ENZ effect in ITO material and the effect of accurate carrier distribution on the performance of a modulator. For this reason, an electro-absorption (EA) modulators with a new configuration based on silicon slot modulator with indium thin oxide material is proposed. To study the effect of ENZ effect in ITO, the semiconductor model (realistic model) is utilized to model the carrier distribution in the ITO material. In this model, there is not any assumption. As a result, by applying the gate voltage, the insertion loss is increased 1.61 dB/μm in comparison with unbiased conditions. Also, the uniform model is used. Compared with the realistic model, the extinction ratio and figure-of- merit significantly enhance based on the uniform model, but the trends of results like insertion loss are so far from the realistic model. It can be found that the realistic model is reliable and the results are closer to reality. Keywords Indium tin oxide . Optical modulator . Electro-absorption . Epsilon-near-zero . Optical waveguides . Optical absorption Introduction In recent years, due to exponentially growing data traffic and cloud-based computing, the telecommunication capacity and wide bandwidth are urgently required [ 1]. This ever- increasing bandwidth demand leads to upgrade the electronic communication system to the optical interconnect system [2]. Silicon photonics has tremendous potential to reduce energy consumption and enhance the bandwidth by using a comple- mentary metal-oxide-semiconductor (CMOS) compatible ap- proach [3, 4]. An optical communication system consists of some essential segments, such as switches and modulators [5, 6]. Among them, the optical modulators attract the huge at- tention of researchers because it can reduce the cost and ener- gy consumption of optical devices [7]. The role of the optical modulator is controlling characteristics of light, such as am- plitude, phase, and polarization. Generally, modulators with a small footprint and large bandwidth are required [8, 9]. Electro-optical (EO) and electro-absorption (EA) are two main effects as modulation techniques which are used in op- tical modulators [10, 11]. As regards the centrosymmetric crystal structure of silicon (Si), the linear EO effect is not observed in Si [12]. On the other hand, the conventional Si electro-optic modulators work with variations of the free car- rier concentration, which is known as the plasma dispersion effect [13]. It is categorized as an EA mechanism. Different types of silicon-based optical modulators have been presented which act based on carrier concentration altering, namely ring resonators, Mach–Zehnder interferometer (MZI), and metal- oxide-semiconductor capacitors [14–16]. Ring resonator modulators are limited by narrow optical bandwidth and tem- perature sensitivity [17]. In spite of ring resonators, MZI mod- ulators have higher bandwidth. Although they have a large footprint in the range of millimeters because of the weak plas- ma dispersion effect in Si [18]. To overcome these limitations and improve the efficiency of modulation, various materials and designs have been suggested to integrate with Si. However, some reported modulators are confined due to the short-range of carrier lifetime and incompatibility with CMOS technology, but also are remarkably efficient in comparison with previous types [1]. Recently, the electro-optic modulators revolutionized by emerging active materials such as graphene * Kambiz Abedi k_abedi@sbu.ac.ir 1 Faculty of Electrical Engineering, Shahid Beheshti University, Tehran, Iran Plasmonics https://doi.org/10.1007/s11468-020-01187-7