Optimization of Hybrid Silicon Lasers for High-Speed Direct Modulation

We report the optimization of hybrid silicon lasers for high-speed direct modulations by studying the small- and large-signal modulation responses based on the simple carrier transport model in this paper. The theoretical model matches well with published experimental data as the same structure parameters are used. To investigate the strong heating effect in hybrid lasers, we apply all of the carrier diffusion/capture and thermionic escape lifetimes to be temperature dependent in simulations. The frequency response of the small-signal analysis shows that the modulation bandwidth is much more sensitive to the temperature and the separate confinement heterostructure (SCH) thickness compared with the other limiting factors, such as the confinement factor, the interlayer thickness, etc. The largest modulation bandwidth decreases from 6.2 to 2.2 GHz under an injection current of 100 mA and an SCH thickness of 80 nm when the temperature rises from 300 to 350 K. The modulation speed will be greatly improved with a thinner SCH layer, particularly the p-type SCH layer, which helps shorten the diffusion lifetime. Furthermore, eye diagrams are also calculated under different bit rates, SCH thicknesses, and temperatures, respectively. With the increase of the temperature or SCH thickness, the quality of eye diagrams becomes worse. It shows that the modulation frequency can reach 10 Gb/s. We believe that this paper can serve as a guideline for the optimization of next-generation high-speed modulated hybrid silicon lasers.