A novel highly efficient grating coupler with large filling factor used for optoelectronic integration

A novel highly efficient grating coupler with large filling factor and deep etching is proposed in silicon-on-insulator for near vertical coupling between the rib waveguide and optical fibre.The deep slots acting as high efficient scattering centres are analysed and optimized.As high as 60% coupling efficiency at telecom wavelength of 1550-nm and 3-dB bandwidth of 61 nm are predicted by simulation.A peak coupling efficiency of 42.1% at wavelength 1546-nm and 3-dB bandwidth of 37.6 nm are obtained experimentally.

Infrared transition properties of vanadium dioxide thin films across semiconductor-metal transition

Vanadium dioxide thin films were fabricated through annealing vanadium oxide thin films deposited by dual ion beam sputtering. X-ray diffraction (XRD), atom force microscopy (AFM), and Fourier transform infrared spectrum (FTIR) were employed to measure the crystalline structure, surface morphology, and infrared optical transmittance. The phase transition properties were characterized by transmittance. The results show that the annealed vanadium oxide thin film is composed of monoclinic VO2, with preferred orientation of (011). The maximum of transmittance change is beyond 65% as the temperature increases from 20 to 80 C. The reversible changes in optical transmittance against temperature were observed. The change rate of transmittance at short wavelength is higher than that at long wavelength at the same temperature across semiconductor-metal phase transition. This phenomenon was discussed using diffraction effect.

Pseudo-Rhombus-Shaped Subwavelength Crossed Gratings of GaAs for Broadband Antireflection

结合的 Holographic 平版印刷术到暴露的光致抗蚀剂的非线性的反应被采用制作多孔的光致抗蚀剂(PR ) 面具。常规点 PR 面具也被产生，并且两个模式被最佳的干燥蚀刻过程变成内在的 GaAs 底层获得穿过的栅栏(SWCG ) 组织模仿蛾眼睛的逐渐变细的 subwavelength。在实验和模拟的比较，源于多孔的面具的仔细包装的 pseudo-rhombus-shaped GaAs SWCG 超过来自点面具的圆锥形的对应物，并且完成一个报导最低平均数光谱 1.1% 的反射。[从作者抽象]

High-performance 4H-SiC junction barrier Schottky diodes with double resistive termination extensions

4H-SiC junction barrier Schottky (JBS) diodes with a high-temperature annealed resistive termination extension (HARTE) are designed, fabricated and characterized in this work. The differential specific on-state resistance of the device is as low as 3.64 m ·cm2 with a total active area of 2.46×10-3 cm2 . Ti is the Schottky contact metal with a Schottky barrier height of 1.08 V and a low onset voltage of 0.7V. The ideality factor is calculated to be 1.06. Al implantation annealing is performed at 1250℃ in Ar, while good reverse characteristics are achieved. The maximum breakdown voltage is 1000 V with a leakage current of 9×10-5 A on chip level. These experimental results show good consistence with the simulation results and demonstrate that high-performance 4H-SiC JBS diodes can be obtained based on the double HARTE structure.

A review of manufacturing technologies for silicon carbide superjunction devices

Superjunction technology is believed to reach the optimal specific on-resistance and breakdown voltage trade-off.It has become a mainstream technology in silicon high-voltage metal oxide semiconductor field effect transistor devices.Numerous efforts have been conducted to employ the same concept in silicon carbide devices.These works are summarized here.

A Small Signal Equivalent Circuit Model for Resonant Tunnelling Diode

我们报导一根反响的通道二极管(RTD ) 小信号等价物电路模型由量电容和量电感组成。模型通过在 InP 底层上制作的实际 InAs/In0.53Ga0.47As/AlAs RTD 被验证。模型参数被在 RTDcurrent 电压(I-V ) 特征的三个不同区域与交流测量数据适合相等的电路模型提取。电子一生，代表搬运人在伪界限仍然是的平均时间在通道过程期间说，也被计算到 be2.09 ps。

Optical absorption enhancement in slanted silicon nanocone hole arrays for solar photovoltaics

We investigate slanted silicon nanocone hole arrays as light absorbing structures for solar photovoltaics via simulation.With only 1-μm equivalent thickness, a maximum short-circuit current density of 34.9 m A/cm^2 is obtained. Moreover, by adding an Ag mirror under the whole structure, a short-circuit current density of 37.9 m A/cm^2 is attained. It is understood that the optical absorption enhancement mainly results from three aspects. First, the silicon nanocone holes provide a highly efficient antireflection effect. Second, after breaking the geometric symmetry, the slanted silicon nanocone hole supports more resonant absorption modes than vertical structures. Third, the Fabry–Perot resonance enhances the light absorption after adding an Ag mirror.

Gate-regulated transition temperatures for electron hopping behaviours in silicon junctionless nanowire transistors

We investigate gate-regulated transition temperatures for electron hopping behaviours through discrete ionized dopant atoms in silicon junctionless nanowire transistors.We demonstrate that the localization length of the wave function in the spatial distribution is able to be manipulated by the gate electric field.The transition temperatures regulated as the function of the localization length and the density of states near the Fermi energy level allow us to understand the electron hopping behaviours under the influence of thermal activation energy and Coulomb interaction energy.This is useful for future quantum information processing by single dopant atoms in silicon.

Quantitative and sensitive detection of prohibited fish drugs by surface-enhanced Raman scattering

Rapid and simple detections of two kinds of prohibited fish drugs, crystal violet(CV) and malachite green(MG),were accomplished by surface-enhanced Raman scattering(SERS). Based on the optimized Au/cicada wing, the detectable concentration of CV/MG can reach 10^(-7) M, and the linear logarithmic quantitative relationship curves between log I and log C allows for the determination of the unknown concentration of CV/MG solution. The detection of these two analytes in real environment was also achieved, demonstrating the application potential of SERS in the fast screening of the prohibited fish drugs, which is of great benefit for food safety and environmental monitoring.

A large bandwidth photonic delay line using passive cascaded silicon-on-insulator microring resonators

This paper investigated the design and the characterization of a photonic delay line based on passive cascaded silicon-on-insulator (SOI) microrings.We considered the compromise of group delay,bandwidth and insertion loss.A 3-stage double channel side-coupled integrated spaced sequence of resonator (SCISSOR) device was optimized by shifting the resonance of each microring and fabricated with electron beam lithography and dry etching.The group delay was measured to be 17 ps for non-return-to-zero signals at different bit rates and the bandwidth of 78 GHz was achieved.The experiment result agreed well with our simulation.

High efficiency and broad bandwidth grating coupler between nanophotonic waveguide and fibre

A high efficiency and broad bandwidth grating coupler between a silicon-on-insulator (SOI) nanophotonic waveguide and fibre is designed and fabricated. Coupling efficiencies of 46% and 25% at a wavelength of 1.55 μm are achieved by simulation and experiment, respectively. An optical 3 dB bandwidth of 45 nm from 1530 nm to 1575 nm is also obtained in experiment. Numerical calculation shows that a tolerance to fabrication error of 10 nm in etch depth is achievable. The measurement results indicate that the alignment error of ±2 μm results in less than 1 dB additional coupling loss.

Electric-field-dependent charge delocalization from dopant atoms in silicon junctionless nanowire transistor

We study electric-field-dependent charge delocalization from dopant atoms in a silicon junctionless nanowire transistor by low-temperature electron transport measurement. The Arrhenius plot of the temperature-dependent conductance demonstrates the transport behaviors of variable-range hopping(below 30 K) and nearest-neighbor hopping(above 30 K).The activation energy for the charge delocalization gradually decreases due to the confinement potential of the conduction channel decreasing from the threshold voltage to the flatband voltage. With the increase of the source–drain bias, the activation energy increases in a temperature range from 30 K to 100 K at a fixed gate voltage, but decreases above the temperature of 100 K.

Electronic transport properties of silicon junctionless nanowire transistors fabricated by femtosecond laser direct writing

Silicon junctionless nanowire transistor(JNT) is fabricated by femtosecond laser direct writing on a heavily n-doped SOI substrate.The performances of the transistor,i.e.,current drive,threshold voltage,subthreshold swing(SS),and electron mobility are evaluated.The device shows good gate control ability and low-temperature instability in a temperature range from 10 K to 300 K.The drain currents increasing by steps with the gate voltage are clearly observed from 10 K to50 K,which is attributed to the electron transport through one-dimensional(1D) subbands formed in the nanowire.Besides,the device exhibits a better low-field electron mobility of 290 cm^2·V^(-1)·s^(-1),implying that the silicon nanowires fabricated by femtosecond laser have good electrical properties.This approach provides a potential application for nanoscale device patterning.

Quantum transport characteristics in single and multiple N-channel junctionless nanowire transistors at low temperatures

Single and multiple n-channel junctionless nanowire transistors(JNTs) are fabricated and experimentally investigated at variable temperatures. Clear current oscillations caused by the quantum-confinement effect are observed in the curve of drain current versus gate voltage acquired at low temperatures(10 K–100 K) and variable drain bias voltages(10 mV–90 mV). Transfer characteristics exhibit current oscillation peaks below flat-band voltage(VFB) at temperatures up to 75 K,which is possibly due to Coulomb-blocking from quantum dots, which are randomly formed by ionized dopants in the just opened n-type one-dimensional(1D) channel of silicon nanowires. However, at higher voltages than VFB, regular current steps are observed in single-channel JNTs, which corresponds to the fully populated subbands in the 1D channel. The subband energy spacing extracted from transconductance peaks accords well with theoretical predication. However, in multiple-channel JNT, only tiny oscillation peaks of the drain current are observed due to the combination of the drain current from multiple channels with quantum-confinement effects.

CMOS compatible highly efficient grating couplers with a stair-step blaze profile

A novel grating coupler with a stair-step blaze profile is proposed.The coupler is a CMOS process compatible device and can be used for light coupling in optical communication.The blaze profile can be optimized to obtain a high efficiency of 66.7% for the out-of-plane coupling at the centre wavelength of 1595 nm with a 1 dB bandwidth of 41 nm.Five key parameters of the stair-step blaze grating and their effects on the coupling are discussed for the application in L band telecommunication.

Influence of dopant concentration on electrical quantum transport behaviors in junctionless nanowire transistors

We discuss the random dopant effects in long channel junctionless transistor associated with quantum confinement effects. The electrical measurement reveals the threshold voltage variability induced by the random dopant fluctuation.Quantum transport features in Hubbard systems are observed in heavily phosphorus-doped channel. We investigate the single electron transfer via donor-induced quantum dots in junctionless nanowire transistors with heavily phosphorusdoped channel, due to the formation of impurity Hubbard bands. While in the lightly doped devices, one-dimensional quantum transport is only observed at low temperature. In this sense, phonon-assisted resonant-tunneling is suppressed due to misaligned levels formed in a few isolated quantum dots at cryogenic temperature. We observe the Anderson-Mott transition from isolate electron state to impurity bands as the doping concentration is increased.

High-responsivity solar-blind photodetector based on MOCVD-grown Si-dopedβ-Ga_(2)O_(3)thin film

Si-dopedβ-Ga_(2)O_(3)films are fabricated through metal-organic chemical vapor deposition(MOCVD).Solar-blind ultraviolet(UV)photodetector(PD)based on the films is fabricated by standard photolithography,and the photodetection properties are investigated.The results show that the photocurrent increases to 11.2 mA under 200μW·cm^(-2)254 nm illumination and±20 V bias,leading to photo-responsivity as high as 788 A·W^(-1).The Si-dopedβ-Ga2O3-based PD is promised to perform solar-blind photodetection with high performance.

Self-powered solar-blind photodiodes based on EFG-grown(100)-dominant β-Ga_(2)O_(3) substrate

We report the edge-defined-film-fed(EFG)-grown β-Ga_(2)O_(3)-based Schottky photodiodes.The device has a reverse leakage current of ~nA and a rectified ratio of ~10^(4) at ±5 V.In addition,the photodiode detector shows a dark current of 0.3 pA,a photo-responsivity(R) of 2.875 mA/W,a special detectivity(D*) of 10^(10) Jones,and an external quantum efficiency(EQE) of 1.4% at zero bias,illustrating a self-powered operation.This work may advance the development of the Ga_(2)O_(3)-based Schottky diode solar-blind photodetectors.

Charge trapping in surface accumulation layer of heavily doped junctionless nanowire transistors

We investigate the conductivity characteristics in the surface accumulation layer of a junctionless nanowire transistor fabricated by the femtosecond laser lithography on a heavily n-doped silicon-on-insulator wafer. The conductivity of the accumulation region is totally suppressed when the gate voltage is more positive than the flatband voltage. The extracted low field electron mobility in the accumulation layer is estimated to be 1.25 cm2·V-1·s-1. A time-dependent drain current measured at 6 K predicts the existence of a complex trap state at the Si–Si O2 interface within the bandgap. The suppressed drain current and comparable low electron mobility of the accumulation layer can be well described by the large Coulomb scattering arising from the presence of a large density of interface charged traps. The effects of charge trapping and the scattering at interface states become the main reasons for mobility reduction for electrons in the accumulation region.