Low-loss silicon photonic electro-optic modulator based on high mobility Mo-doped In2O3 thin films

Transparent conductive oxides (TCO) have attracted considerable attention in on-chip silicon photonic devices owing to CMOS compatibility, excellent optical confinement, and modulation effect. However, the relatively high intrinsic losses limit its application in large-scale integration. In this work, molybdenum-doped and tin-doped indium oxide (IMO and ITO) were prepared and their electro-optic modulation performance was investigated. Compared with ITO, IMO offers significant advantages in the near-infrared region: the extinction coefficient at 1.55 μm is dramatically reduced from 0.85 to 0.15, corresponding to higher transmittance. Furthermore, the mobility reaches 54 cm 2 /(V·s), more than twice that of ITO, which is attributed to the reduced electron effective mass in IMO. Finite-element simulations of an IMO-based hybrid plasmonic modulator (HPM) at 1.55 μm reveal an insertion loss as low as 2.8 dB, a modulation depth of 2 dB, and a figure of merit V πL of 0.24 V mm. A bandwidth of 72 GHz is projected based on RC-limited analysis with further structural optimization. These results demonstrate that high-mobility IMO enables low-loss, compact phase shifters, offering a promising route toward on-chip silicon photonic integration with both low propagation loss and high modulation efficiency.