High-Quality Graphene-Based Tunable Absorber Based on Double-Side Coupled-Cavity Effect

Graphene-based devices have important applications attributed to their superior performance and flexible tunability in practice. In this paper, a new kind of absorber with monolayer graphene sandwiched between two layers of dielectric rings is proposed. Two peaks with almost complete absorption are realized. The mechanism is that the double-layer dielectric rings added to both sides of the graphene layer are equivalent to resonators, whose double-side coupled-cavity effect can make the incident electromagnetic wave highly localized in the upper and lower surfaces of graphene layer simultaneously, leading to significant enhancement in the absorption of graphene. Furthermore, the influence of geometrical parameters on absorption performance is investigated in detail. Also, the device can be actively manipulated after fabrication through varying the chemical potential of graphene. As a result, the frequency shifts of the two absorption peaks can reach as large as 2.82 THz/eV and 3.83 THz/eV, respectively. Such a device could be used as tunable absorbers and other functional devices, such as multichannel filters, chemical/biochemical modulators and sensors.

Fabrication of Perovskite Film-Coated Hollow Capillary Fibers Using a Fast Solvent Exchange Method

Metal halide perovskites have been successfully applied in a variety of fields such as LEDs, lasers and solar cells, thanks to their excellent optoelectronic properties. Capillary fibers can further expand the range of perovskite applications and at the same time improve its stability by encapsulating the perovskite inside the capillary. However, the high-quality perovskite film-coated hollow capillary fibers have yet to be realized. Here, we introduce a fast solvent exchange method which is used for the preparation of neat and smooth perovskite films deposited on the inner surface of capillary fibers. We demonstrate that this fast solvent exchange method is superior to the commonly used spontaneous diffusion-based precipitation method. The obtained hollow capillary fibers show a narrowed spectral width of 4.9 nm under pulse excitation due to the optical cavity effect. This new fabrication method can facilitate the development of perovskites in the fields of capillary lasing, microfluidic sensing, flexible LEDs and luminous fabrics.

High Performance p-i-n Photodetectors on Ge-on-Insulator Platform

In this article, we demonstrated novel methods to improve the performance of p-i-n photodetectors (PDs) on a germanium-on-insulator (GOI). For GOI photodetectors with a mesa diameter of 10 μm, the dark current at −1 V is 2.5 nA, which is 2.6-fold lower than that of the Ge PD processed on Si substrates. This improvement in dark current is due to the careful removal of the defected Ge layer, which is formed with the initial growth of Ge on Si. The bulk leakage current density and surface leakage density of the GOI detector at −1 V are as low as 1.79 mA/cm2 and 0.34 μA/cm, respectively. GOI photodetectors with responsivity of 0.5 and 0.9 A/W at 1550 and 1310 nm wavelength are demonstrated. The optical performance of the GOI photodetector could be remarkably improved by integrating a tetraethylorthosilicate (TEOS) layer on the oxide side due to the better optical confinement and resonant cavity effect. These PDs with high performances and full compatibility with Si CMOS processes are attractive for applications in both telecommunications and monolithic optoelectronics integration on the same chip.