Mu Ku Chen

Transferring the bendable substrateless GaN LED grown on a thin C-rich SiC buffer layer to flexible dielectric and metallic plates

By growing an epitaxial GaN LED on C-rich a-SiC buffer deposited SiO2/Si substrate, the simplified transfer to versatile flexible metallic/dielectric membranes is demonstrated. Both the high growth temperature at 1000 °C and the slow deposition rate played important roles in the meticulous MOCVD growth of n-GaN along the surface normal of the a-SiC at the very beginning. High substrate temperature facilitated the refinement of C-rich SiC buffer from amorphous to partially crystalline with (0004)-orientation, which effectively reduces the lattice mismatch between n-GaN and SiC at the interface so as to gradually improve the crystalline n-GaN regrowth. The substrateless GaN LED transferred to flexible copper plates showed reduced turn-on voltage of 2.6 V, enhanced output power of 370 mW, enlarged power-to-current slope of 1.24 W A−1, increased external quantum efficiency of 45%, and reduced efficiency droop of 15% under a bias of 300 mA. The thermal conductivity of the transferred substrate affected the EL peak wavelength shift of the substrateless GaN LED on SiC buffer. Heating the GaN LED on flexible copper plate to 65 °C only reduced its power by 10% and red-shifted its wavelength by 1 nm under a bias at 100 mA; the Auger effect resulted in a degraded EQE of 39.1% and an enlarged EQE droop of 8.5%. Bending the surface diameter of the curvature of the copper plate to 1.2 cm decayed the output power by 12% and red-shifted the EL peak by 5 nm because of the lattice strain induced quantum confined Stark effect (QCSE). Such a bendable substrateless GaN LED transferred to flexible membrane with superior heat dissipation and bending tolerance is a desired lighting element for green photonics in this era.

Optical toroidal response in three-dimensional plasmonic metamaterial

Toroidal dipole moments, the third kind of fundamental dipole moment, have unusual electromagnetic properties different from the electric and magnetic multipoles. We fabricate a new type of 3D plasmonic toroidal metamaterial by using mutual coupling between dumbbell-shaped gold apertures with vertical split-ring resonators (VSRRs) at optical frequency. The radiated power of multipole moments are calculated and analyzed to improve the meta-system is dominated by the toroidal dipole moment. This result paves a way for practical application on metamaterial based devices, such as biosensor and lasing spaser.

Metalens for structure light

Here we demonstrated a GaN metalens array to project a light spots array which can be a light shape generator in the structure light applications. The advantages of this metadevice is light weight, small, ultrathin, durable and easy to compact with other device. The light spot size is a function with the distance of detector. A metalens array which arranged by the single metalens diameter is 20 μm projected a light spots array whose diameter of single light spot is 2.22 um in average at the distance is 150 cm far away and. Our design provides a new avenue for the structure light application such as distance sensing and 3D environmental construction.

Metalens for distance estimation (Conference Presentation)

Metalenses have great ability in light focusing and can be tailored to exhibit varied functionalities for ultrathin optical applications. Here, we demonstrate a GaN metalens array which can be regarded as a light shaping generator for the structured light generation. The metalens array consists of 60 x 60 metalenses which can project a 42 cm x 42 cm light spots area at the distance of 1.5 M. The distance can be estimated by identifying the deformation of light spot distribution. The advantages of this metadevice is light weight, small, ultrathin, durable and easy to compact with other devices. Our design provides a new avenue for the structured light applications such as distance sensing and 3D environmental construction.

Plasmon coupling in vertical split-ring resonator magnetic metamolecules

Vertical split-ring resonators (VSRRs) were fabricated which behave as magnetic metamolecules sensitive to both incident electric and magnetic fields with the stronger induced magnetic dipole moments upon excitation in comparison to planar SRRs. Using these metamolecules with different spacing in VSRR dimers, we investigate the hybridization of the magnetic plasmon modes associated with each constituent VSRRs. We found that plasmon coupling can be precisely controlled by varying the gap separation between VSRRs. The resulting wide tuning range of these hybrid modes offers the possibility of developing frequency selective functional devices such as sensors and filters based on plasmon coupling with high sensitivity.

Plasmonic enhanced optical disk reactor for wastewater treatment

A process of growing large-area plasmonic-nano-particles-decorated ZnO nanorods on the polycarbonate optical disk substrate was developed, while a corresponding photocatalytic rotational reactor was fabricated. Hydrothermal process was adapted to grow ZnO nanorods perpendicular to the optical disk substrate at relatively lower temperature. The optical disk substrate has advantages of durable property in fast rotation and high impact-resistance. The plasmonic nano-particles, in this case, silver nano-particles, were deposed on the ZnO nanorods by direct sputtering. The morphology of ZnO nanorods and plasmonic nano-particles was investigated by Scanning Electron Microscope (SEM). The photocatalytic activity of the sample was evaluated by the degradation of methyl orange (MO) as a model compound in aqueous solution, and the decomposition rate of MO molecules is monitored by the optical spectroscopy measurements. In the optimized condition, less than 10% of the MO remained in the aqueous solution after a 20-minute treatment in the rotational reactor with our sample.