Epitaxial growth of III-V micro-ring lasers for integrated Silicon photonics

Fig. 1 Schematic and actual SEM photo of a III-V micro-ring and bus waveguide structures.

Over the last decades, Si photonics has emerged as a promising technology that offers on-chip optical information processing capability. Despite previous successes in fabricating many Si-based on-chip photonic components, the inefficient radiative carrier recombination in Si due to its indirect bandgap makes Si-based on-chip light sources extremely difficult to fabricate.

III-V semiconductor materials, on the other hand, have been widely studied and fabricated into solid-state lasers due to their excellent optical properties, resulting from efficient radiative carrier recombination across their direct energy bandgap. Therefore, integrating III-V semiconductor lasers as on-chip light sources on Si platform offers a solution that can provide
superior optical performance and CMOS-compatibility at the same time.

Micro-ring lasers are micro-structures which do not require feedback mirrors because the resonator cavity is based on whispering gallery modes travelling within the ring cavity, as illustrated in Figure 1. Light output from the micro-ring laser can then be evanescently coupled out to a bus waveguide on the Si substrate.

However, the major complication in the epitaxial growth of III-V materials on Si substrate revolves around the signicant lattice mismatch. Lattice mismatch at the heteroepitaxial interface is known to introduce crystal lattice defects such as misfit dislocations and threading dislocations, which will act as non-radiative recombination centers for carriers and deteriorate the optical properties of grown structures.

In this project, indium phosphide (InP)-based micro-ring lasers will be epitaxially grown on Si substrate using the selective area metal-organic chemical vapour deposition (SA-MOCVD) method and defect trapping techniques such as Epitaxial Lateral Overgrowth (ELOG) and Aspect Ratio Trapping (ART). The aim of this project is to demonstrate a CMOS-compatible fabrication process to integrate III-V micro-ring lasers on to Si substrate, and to study in detail the morphology, crystal structural properties, and optical properties of the fabricated micro-ring lasers. Successful demonstration of functional laser device from this project will mark a signicant milestone towards the realisation of nano-scale Si photonics technology.