High-speed optical modulation by III-V/Si hybrid MOS optical modulator with low parasitic capacitance

摘要

A high-speed Si optical modulatorwith low energy consumption is central to cloud datacenters. Si metal-oxide-semiconductor (MOS) opticalmodulators are attractive in terms of the balancebetween modulation efficiency and modulationbandwidth. In our previous study, a high-efficiencyⅢ-Ⅴ/Si hybrid MOS optical modulator, enabled bybonding a thin n-type InGaAsP membrane on a p-typewaveguide, was reported . Compared with its Sicounterparts, the modulation efficiency was enhancedby a factor of 5–8 with only one tenth opticalabsorption.To achieve a high-speed optical modulation, a lowresistance-capacitance (RC) constant is crucial. Asshown in Fig. 1(a), in the previous demonstration, a 1-μm-wide Si rib waveguide was used for largefabrication tolerance. As a result, the RC constant wasincreased without benefiting the modulationefficiency. Moreover, a Ⅲ-Ⅴ membrane had to lay onSi terraces on the both sides of the Si waveguide toachieve robust wafer bonding, leading to largeparasitic capacitances between the Ⅲ-Ⅴ membraneand Si terraces. In addition, an electrode was directlycontacted with a moderately doped n-type InGaAsPlayer, making it difficult to achieve a low contactresistivity. Similarly, the doping density of the Si layerwas not high enough to enable a low-resistivitycontact.