Novel Hetero-Integrated Photonic Devices and Flexible Optical Applications Enabled by Van der Waals Integration

Today, electronic and photonic devices are ubiquitous in smartphones, computers, light sources, sensors, and communications. To support the demand for optoelectronic applications, functional materials are essential. For example, silicon is required for logic computing and optical integrated circuits (PIC); Group III-V semiconductors (such as GaAs, InP, AlN, etc.) are used in optoelectronics, light emission and photodetection applications; and piezoelectric materials for actuators and sensors.

However, the development of multifunctional and versatile photonic and optoelectronic systems would benefit from achieving all required functionality using a single material platform. Hence, the heterogeneous integration platform has attracted tremendous interest from academic and industry circles. Our research group (led by Professor Sang Hoon Pae of Washington University in St. Louis, WUSTL) sought to address this need by utilizing advanced adhesive and layer transfer technology for novel optoelectronic applications.

Heterogeneous integration of functional materials and optical structures is essential for building high-performance integrated optoelectronic systems and an ideal platform for investigating nanoscale photonic phenomena. Traditional approaches for this rely on heterogeneous variance and require network matching and process compatibility limitations. When the lattice constant differs by more than a few percentage points between the depilation layer and the substrate, the polycrystalline phase-grown films can deteriorate or only epitaxial islands form, which greatly degrades the intrinsic performance of the optical materials.

However, van der Waals integration (vdW), which takes advantage of isolated independent building blocks, is free from the network matching limitations that apply in epitaxy. This low-energy physical aggregation method was originally applied in 2D materials due to its high flexibility in building vdW heterostructures (see figure above). Recent advances in advanced 2D material-assisted layer removal techniques have provided photonic engineers with many three-dimensional (3D) single-crystalline nanomembranes that can also be fabricated to be very thin, flexible and self-contained, like 2D materials. Thus there has been exciting progress recently in photovoltaic and optoelectronic applications through vdW photonic integration.

In our recent research paper published in Nature reviews materials, we presented a comprehensive catalog of the latest progress in vdW photonic integration from 2D materials to 3D nanomembranes, together with Professor Cheng-Wei Qiu (National University of Singapore), Professor Lan Yang (WUSTL), and Professor Jin-Wook Lee (Sungkyunkwan University), Professor Yang Yang (University of California, Los Angeles) and other international collaborators. In addition to the 2D materials, we also summarized the currently available 3D free-standing nanomembranes. Detailed guidance from thin-film formulations to device applications is also specified.

Since the library of materials available for functional 3D nanofilms is much broader than that for 2D materials, we envision emerging opportunities for van der Waals integration beyond 2D materials: high-quality 3D thin films with modular functions such as optical gain, piezoelectricity, and electrical transferability. Materials – photonics, magneto-optics, etc., to photonic structures to prototypes for new devices and applications.

In this paper, we also identify promising opportunities for mixed-dimensional vdW heterostructures, advanced high-performance photonic devices based on novel heterointegration mappings, and biocompatible and flexible optoelectronic applications based on current perspectives. We also reviewed key technological challenges such as scalable nanofilm fabrication and transfer in the field of thin-film photonics and photonic integration with vdW.

This story is part of Science Dialogue Xwhere researchers can report results from their published research articles. Visit this page For information about ScienceX Dialog and how to participate.

Dr. Yuan Meng is a Postdoctoral Research Associate in the Department of Mechanical Engineering and Materials Science, Washington University in St. Louis, USA. Dr. Sang Hoon Pae is Assistant Professor in the Department of Mechanical Engineering and Materials Science, Washington University in St. Louis, USA.