Phase Change Metasurfaces by Continuous or Quasi-Continuous Atoms for Active Optoelectronic Integration

In recent decades, metasurfaces have emerged as an exotic and appealing group of nanophotonic devices for versatile wave regulation with deep subwavelength thickness facilitating compact integration. However, the ability to dynamically control the wave–matter interaction with external stimulus is highly desirable especially in such scenarios as integrated photonics and optoelectronics, since their performance in amplitude and phase control settle down once manufactured. Currently, available routes to construct active photonic devices include micro-electromechanical system (MEMS), semiconductors, liquid crystal, and phase change materials (PCMs)-integrated hybrid devices, etc. For the sake of compact integration and good compatibility with the mainstream complementary metal oxide semiconductor (CMOS) process for nanofabrication and device integration, the PCMs-based scheme stands out as a viable and promising candidate. Therefore, this review focuses on recent progresses on phase change metasurfaces with dynamic wave control (amplitude and phase or wavefront), and especially outlines those with continuous or quasi-continuous atoms in favor of optoelectronic integration.

Study on Carrier Mobility Model for PD-Ge Monolithic Optoelectronic Integration Chips

Based on the difference of thermal expansion coefficient between Si and Ge, low-intensity tensile stress can be introduced into Ge epitaxial layer on Si substrate. S-Ge/Si semiconductor (as known as low tensile strained Ge grown on Si substrate) has a higher carrier mobility when compared with unstrained-Ge or Si material, so that s-Ge/Si is appropriate for the production of high-speed circuit. At the same time, transformation from indirect bandgap semiconductor Ge into Pseudo-Direct bandgap semiconductor (which is also called PD-Ge) will be happen after s-Ge/Si is heavy doped, which makes LED produced of PD-Ge material perform a higher luminous efficiency because the radiative recombining probability of carriers in PD-Ge material is greatly improved compared with unstrained one. Taking the advantages referred of s-Ge/Si into account, s-Ge/Si has the potential to PD-Ge monolithic optoelectronic integration. Carrier mobility of the semiconductor is one of the key physical parameters during the design and simulation of PD-Ge monolithic optoelectronic integrated system. While as far as the authors are aware, carrier mobility model of s-Ge/Si is still rarely reported to date. In view of that all above, based on the E-k relation in both conduction band and valence band of s-Ge/Si material, the analytical models of physical parameters in energy band are established, and the models are verified by experiments. Then the s-Ge/Si carrier models are further established based on our band structure model, and the Monte Carlo method is used to verify our s-Ge/Si carrier mobility model. The quantificational results of our paper will help understand s-Ge/Si material physics and provide an important theoretical basis for the design of PD-Ge monolithic optoelectronic integration.