A planar chiral nanostructure with asymmetric transmission of linearly polarized wave and huge optical activity in near-infrared band

Just like an electronic diode that allows the electrical current to flow in one direction only, a kind of chiral metamaterial structure with a similar functionality for the electromagnetic wave is proposed. The designed nanostructure that consists of twisted metallic split-ring resonators on both sides of a dielectric substrate achieves asymmetric transmission for a forward and backward propagating linearly polarized wave by numerical simulation in near-infrared band. Difference in transmission efficiency of the optimized structure between the same polarized waves incident from opposite directions can reach a maximum at the communication wavelength （1.55 μm）. Moreover, the simulation results of this structure also exhibit strong optical activity and circular dichroism.

Assessing high-energy x-ray and proton irradiation effects on electrical properties of P-GaN and N-GaN thin films

The effects of ionizing and displacement irradiation of high-energy x-ray and 2-MeV proton on GaN thin films were investigated and compared in this study.The electrical properties of both P-GaN and N-GaN,separated from power devices,were gauged for fundamental analysis.It was found that the electrical properties of P-GaN were improved as a consequence of the disruption of the Mg-H bond induced by high-dose x-ray irradiation,as indicated by the Hall and circular transmission line model.Specifically,under a 100-Mrad(Si)x-ray dose,the specific contact resistance pc of P-GaN decreased by 30%,and the hole carrier concentration increased significantly.Additionally,the atom displacement damage effect of a 2-MeV proton of 1×10^(13)p/cm^(2)led to a significant degradation of the electrical properties of P-GaN,while those of N-GaN remained unchanged.P-GaN was found to be more sensitive to irradiation than N-GaN thin film.The effectiveness of x-ray irradiation in enhancing the electrical properties of P-GaN thin films was demonstrated in this study.

Optimization of ohmic contact for InP-based transferred electronic devices

The effect of the annealing time and annealing temperature on Ni/Ge/Au electrode contacts deposited on the n-type InP contact layer has been studied using a circular transmission line model. The minimum specific contact resistance of 3.210 7 cm2was achieved on the low-doped n-type InP contact layer with a 40 s anneal at 425 ℃. In order to improve the ohmic contact and reduce the difficulty in the fabrication of the high doped InP epi-layer, the doping concentration in the InP contact layer was chosen to be 51018cm 3in the fabrication of transferred electronic devices. Excellent differential negative resistance properties were obtained by an electron beam evaporating the Ni/Ge/Au/Ge/Ni/Au composite electrode on an InP epi-layer with a 60 s anneal at 380 ℃.