Nanomaterials and High-Contrast Metastructures for Integrated Optoelectronics
Integrated optoelectronics has demonstrated its great potential in numerous fields. In the past decade, its applications have rapidly expanded from the conventional long-haul optical communication to emerging areas such as data center, consumer electronics, energy harnessing, environmental sensing, and biological imaging. This revolutionary progress benefits from the advancement in light generation, manipulation, detection and its interaction with other systems. Device innovation is the key in this advancement. My dissertation discusses this innovation from two aspects: the integration of nanomaterials and the incorporation of metastructures in optoelectronic devices.
The first topic focuses on material integration to facilitate on-chip optoelectronic devices. As microprocessors become progressively faster, chip-scale data transport has turned progressively more challenging. Optical interconnects for inter- and intra-chip communications are required to reduce power consumption and increase bandwidth. Integrating III-V compound semiconductors with superior optical proficiencies onto the silicon-based microelectronic backbone can pave the way towards a highly compact optoelectronic platform, combing the strengths of both materials. The direct growth of III-V micropillars on silicon substrate in the unique growth mode and under CMOS-compatible condition can yield single-crystal structures in sizes exceeding lattice-mismatched critical dimensions. These micropillars overcome the drawbacks of conventional nanowires, thus are endued with superior optical characteristics for on-chip lasers, photodetectors, and cost-effective solar cells. I will discuss the optical characterization of InP micropillars directly grown on silicon, and the optimization of their optical properties. The excellent material quality and device performance of these InP micropillars show promise for a variety of integrated optoelectronic devices.
The second topic centers at the function integration enabled by high-contrast subwavelength grating (HCG), on the platform of vertical-cavity surface-emitting lasers (VCSELs). VCSELs are key light sources in integrated optoelectronics, with the advantages of low power consumption, low packaging cost, and ease of fabrication into arrays for wafer-scale testing. Mode-hop-free, fast and widely tunable VCSELs are also an ideal candidate for the emerging swept-source optical coherence tomography (SS-OCT) as well as light detection and ranging (LiDAR) applications. I will investigate how HCG, an ultrathin monolithic layer of sub-wavelength metastructure, can function as a highly reflective broadband mirror to facilitate lasing of VCSEL. Widely tunable HCG-VCSELs emitting at 1060-nm are demonstrated, a prevalent light source in SS-OCT for 3D eye imaging. Besides functioning as a tunable mirror, the HCG can also be designed as an integrated beam-shaping element at the same time. The rich properties and the large design space of HCG enable direct tailoring of the output beam features of VCSELs, such as transverse-mode control and far-field emission patterning with angular and spatial modulations by HCG. This opens new avenues for direct laser beam shaping with a monolithic optical element for integrated optoelectronics.