Gongli Xiao

Tunable band-stop plasmonic waveguide filter with symmetrical multiple-teeth-shaped structure.

A nanometeric plasmonic filter with a symmetrical multiple-teeth-shaped structure is investigated theoretically and numerically. A tunable wide bandgap is achievable by adjusting the depth and number of teeth. This phenomenon can be attributed to the interference superposition of the reflected and transmitted waves from each tooth. Moreover, the effects of varying the number of identical teeth are also discussed. It is found that the bandgap width increases continuously with the increasing number of teeth. The finite difference time domain method is used to simulate and compute the coupling of surface plasmon polariton waves with different structures in this Letter. The plasmonic waveguide filter that we propose here may have meaningful applications in ultra-fine spectrum analysis and high-density nanoplasmonic integration circuits.

Improving breakdown voltage performance of SOI power device with folded drift region

A novel silicon-on-insulator (SOI) high breakdown voltage (BV) power device with interlaced dielectric trenches (IDT) and N/P pillars is proposed. In the studied structure, the drift region is folded by IDT embedded in the active layer, which results in an increase of length of ionization integral remarkably. The crowding phenomenon of electric field in the corner of IDT is relieved by the N/P pillars. Both traits improve two key factors of BV, the ionization integral length and electric field magnitude, and thus BV is significantly enhanced. The electric field in the dielectric layer is enhanced and a major portion of bias is borne by the oxide layer due to the accumulation of inverse charges (holes) at the corner of IDT. The average value of the lateral electric field of the proposed device reaches 60 V/μm with a 10 μm drift length, which increases by 200% in comparison to the conventional SOI LDMOS, resulting in a breakdown voltage of 607 V.

Significantly increased surface plasmon polariton mode excitation using a multilayer insulation structure in a metal-insulator-metal plasmonic waveguide.

In this paper, we propose a novel multilayer insulation structure in a metal-insulator-metal (MIM) plasmonic waveguide to explore the possibility of increasing surface plasmon polariton (SPP) mode excitation. Numerical investigations show that the effective refractive index of the multilayer insulation structure affects symmetric SPP mode excitation. The significant enhancement of electric field intensity in horizontal and vertical profiles with a dipole in SiO2 compared with in Al2O3 is observed in the proposed MIM plasmonic waveguides due to a combination of the improved optical density and dipole radiation intensities under a low refractive index. The Au/SiO2/Al2O3/SiO2/Au geometry shows the best enhancement performances, which can serve as an excellent guideline for designing and optimizing a high-performance SPP source using a multilayer insulation structure.

Transmission enhancement properties of double-layered metallic hole arrays

We report experimental results on enhanced light transmission through double-layered (Ag/Au) metallic hole arrays within a skin-depth. Zero-order transmission spectrums are characterized as a function of Ag films thickness, which extends from \delta/15, \delta/6 to approximately \delta, where \delta is a skin-depth. In contrast with other reported results (Refs.[11-13]) in single-layered metallic hole arrays, our experimental results show much more dramatic properties of transmission process dependent on sub- thickness. It is shown that there is no negligible transmission enhancement at \delta/16. At \delta/6, much higher transmission efficiency can be achieved. With films thickness being close to \delta, the transmission efficiency declines contrarily. Simultaneously, the corresponding resonant peak also slightly moves toward the shorter wavelength. It is proposed that the coupling of surface plasmon polaritons (SPPs) at Ag/Au interface within is involved in the process.

A highly efficient surface plasmon polaritons excitation achieved with a metal- coupled metal-insulator-metal waveguide

We propose a novel metal-coupled metal-insulator-metal (MC-MIM) waveguide which can achieve a highly efficient surface plasmon polaritons (SPPs) excitation. The MC-MIM waveguide is formed by inserting a thin metal film in the insulator of an MIM. The introduction of the metal film, functioning as an SPPs coupler, provides a space for the interaction between SPPs and a confined electromagnetic field of the intermediate metal surface, which makes energy change and phase transfer in the metal-dielectric interface, due to the joint action of incomplete electrostatic shielding effect and SPPs coupling. Impacts of the metal film with different materials and various thickness on SPPs excitation are investigated. It is shown that the highest efficient SPPs excitation is obtained when the gold film thickness is 60 nm. The effect of refractive index of upper and lower symmetric dielectric layer on SPPs excitation is also discussed. The result shows that the decay value of refractive index is 0.3. Our results indicate that this proposed MC-MIM waveguide may offer great potential in designing a new SPPs source.

The Transmission Characteristics of Asymmetrical Multi-Teeth-Shaped Plasmonic Waveguide Structure

The transmission characteristics of asymmetrical multi-teeth-shaped plasmonic waveguide structure are investigated theoretically and numerically. The tunable dual flat bandgaps are achieved in our proposed structure. This feature can provide a promising application for plasmonic bandstop filter. In addition, according to the hybrid effects of the first order resonance and high order resonance of N identical asymmetrical teeth, a sharp transmission peak can be obtained. This peak, which is within two bandgaps, possesses a relative small full-width at half-maximum, about 11.5 nm. Moreover, the resonant wavelength of this sharp peak can be regulated by adjusting the relative depths of N asymmetrical teeth. These results that we acquire may have important application potential on high-density nanoplasmonic integration circuits.

Effect of the ratio of hole radius to lattice spacing on transmission characteristics for metal/dielectric photonic crystal

In this work, the effect of the ratio of hole radius to lattice spacing (r/a0) on transmission characteristics for the metal/dielectric photonic crystal (MDPC) is investigated. The relationship between the photonic band gap (PBG) dependent on r/a0 is discussed. This is because the characteristics of the PBG dependent on r/a0 affect transmission characteristics for MDPC. The plane wave method (PWM) is used to simulate the PBG by changing r/a0 from 0.2 to 0.3. For hexagonal arrays, we find that with r/a0 being 0.25, the desired PBG structure is achieved. The experimental study for hexagonal air holes arrays residing in the Au@SiO2@Si structure by changing r/a0 from 0.2 to 0.3 is presented. The result shows that with r/a0 being 0.25, a narrow bandwidth and high efficiency transmission is achieved. It is demonstrated that the distinct effect of r/a0 on transmission characteristics for MDPC structure.

Dual-band perfect absorbers based on the magnetic resonance and the cavity resonance

An infrared (IR) absorber based on the metamaterial structure is proposed theoretically and numerically. The near-unity absorption can be achieved at a certain wavelength by optimizing geometrical parameters of the structure. Moreover, we can switch a single-band absorber to dual-band absorber by decreasing the thickness of top metallic layer which is perforated by an air-filled ribbon. At the same time, we confirm that the mechanism of this two absorption bands is completely different. The simultaneous effects of the magnetic resonance and the cavity resonance occur at our proposed structure. Besides according to the control of polarization direction, the absorption peaks occur at the two constant wavelengths, and the superposed value of this two absorption peaks is always close to a constant. Based on this phenomenon, a simple dual-band absorber is designed when the thickness of top shaped metallic film is relatively large. The cavity response is not the existence in this condition. These results that we obtain may provide some promising applications such as sensors, thermal imagers, and IR detectors.

The effect of nitridation and sulfur passivation for In0.53Ga0.47As surfaces on their Al/Al2O3/InGaAs MOS capacitors properties*

The impact of nitridation and sulfur passivation for In0 53Ga0 47As surfaces on the Al/Al2O3/InGaAs MOS capacitors properties was investigated by comparing the characteristics of frequency dispersion and hysteresis, calculating the Dit and ΔNbt values, and analyzing the interface traps and the leakage current. The results showed that both of the methods could form a passivation-layer on the InGaAs surface. The samples treated by N2 plasma could obtain good interface properties with the smallest frequency dispersion in the accumulation region, and the best hysteresis characteristics and good I–V properties were presented. Also the samples with (NH4/2Sx treatment showed the smallest frequency dispersion near the flat-band region and a minimum Dit value of 2.6 × 1011 cm−2 eV−1.

Enhanced middle-infrared light transmission through Au/SiO x N y /Au aperture arrays

The enhanced middle-infrared light transmission through Au/SiO x N y /Au aperture arrays by changing the refractive index and the thickness of a dielectric layer was studied experimentally. The results indicated that the transmission spectrum was highly dependent on the refractive index and the thickness of SiO x N y . We found that the transmission peaks redshifted regularly along with the refractive index from 1.6 to 1.8, owing to the role of surface plasmon polaritons (SPP) coupling in the Au/SiO x N y /Au cascaded structure. Simultaneously, a higher transmission efficiency and narrower transmission peak was obtained in Au/SiO 2.1 N 0.3 /Au cascaded structure with small refractive index (1.6) than in Au/ SiO 0.6 N1/Au cascaded structure with large refractive index (1.8). When the thickness of SiO x N y changes from 0.2 to 0.4 µm, the shape of transmission spectrum exhibits a large change. It was found that a higher transmission efficiency and narrower transmission peak was obtained in Au/SiO x N y /Au cascaded structure with a thin dielectric film (0.2 µm), with the increase of SiO x N y films thickness, the transmission peak gradually widened and disappeared finally. This effect is useful in applications of biochemical sensing and tunable integrated plasmonic devices in the middle-infrared region.