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In this paper, we present the design, fabrication, and measurement of an evanescently coupled waveguide photodetector operating at 1.55 μm, which mainly comprises a diluted waveguide, a single-mode rib waveguide and a p—i—n photodiode with an extended optical matching layer. The optical characteristics of this structure are studied by using a three-dimensional finite-difference time-domain (3D FDTD) method. The photodetector exhibits a high 3-dB bandwidth of more than 35 GHz and a responsivity of 0.291 A/W at 1550 nm directly coupled with a cleaved fiber. Moreover, a linear response of more than 72-mW optical power is achieved, where a photocurrent of more than 21 mA is obtained at a reverse bias voltage of 3 V. [ABSTRACT FROM AUTHOR]

With first-principles virtual-crystal approximation calculations, we systematically investigate the geometric and electronic structures as well as the phase transition of lead zirconate titanate (PbZr1-xTixO3 or PZT) as a function of Ti content for the whole range of 0 ⩽ xTi ⩽ 1. It can be found that, with the increase of the Ti content, the PbZr1-xTixO3 solid solutions undergo a rhombohedral-to-tetragonal phase transition, which is consistent with the experimental results. In addition, we also show the evolution in geometric and electronic structures of rhombohedral and tetragonal PbZr1-xTixO3 with the increasing content of Ti. [ABSTRACT FROM AUTHOR]

The P+ a-SiC:H/N+ poly-Si solar cell is simulated by an AMPS-1D device simulator to characterize the new thin film polycrystalline-silicon solar cell. In order to analyze the characteristics of the device, the thickness, working temperature, and impurity concentration for the N+ polysilicon layer are considered. The results show that the performance of the cells shows little change when the thickness of N+ polysilicon varies from 10 to 30 μm. It is concluded that the P+ a-SiC:H/N+ poly-Si solar cell has the highest performance with high open circuit voltages (Voc) of 1.31 V, high conversion efficiency of 17.363% and high fill factor of 0.884. Therefore, the P+ a-SiC:H/N+ poly-Si solar cell has promising future applications [ABSTRACT FROM AUTHOR]

The differences in structural change between Au225 and Au369 clusters with their (111) facets supported on MgO(100) surfaces at 5 K are studied by using molecular-dynamics simulations with the atomic interchange potentials of the Au/MgO interface. The parameters are obtained from the ab initio energies using the Chen-Möbius inversion method. Analyses of the pair distribution functions show that the two Au clusters use different deformation processes to adjust the distances between the interface atoms, owing to the misfit between the atom distances among the clusters and the substrates. The local structural changes are identified by atomic density profiles. [ABSTRACT FROM AUTHOR]

Tunable metamorphic InGaAs partially depleted absorber photodiodes with resonant cavity enhanced structure are fabricated on GaAs substrate. Dark-current densities of 7.2 × 10-7 A/cm2 at 0V and 3.6 × 10-4 A/cm2 at -5 V, a high quantum efficiency of 74.4 % at 1546 nm, and a 3-dB bandwidth up to 12 GHz are achieved. The full width at half maximum of the detector is about 16 nm. Furthermore, through thermal tuning, the peak wavelength red shifts from 1527nm to 1544 nm, and a tuning range of 17nm is realized without fabricating extra tuning electrodes. [ABSTRACT FROM AUTHOR]

The good quality of 200 pairs of highly strained Ino.24GaAs/GaAs multi-quantum-well (MQW) structure is demonstrated by the x-ray diffraction and photoluminescence curves. Large-area modulators based on the pseudomorphic Ino.24GaAs/GaAs MQW are designed and fabricated successfully, where the diameters are not less than 3mm and the working wavelength is extended to 1064nm. The single pass modulation depth is demonstrated to be 0.34 at 1064 nm at a reverse voltage of 80 V . [ABSTRACT FROM AUTHOR]

A hydrogen-plasma-etching-based plasma-enhanced chemical vapor deposition (PECVD) synthesis route without metal catalyst for preparing the graphene films on flexible glass is developed. The quality of the prepared graphene films is evaluated by scanning electron microscopy, x-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, ultraviolet-visible spectroscopy, and electrochemical measurements. In a radio frequency (RF) power range of 50 W–300 W, the graphene growth rate increases with RF power increasing, while the intensity ratio of D- to G-Raman peak (ID/IG) decreases. When the RF power is higher than 300 W, the ID/IG rises again. By optimizing experimental parameters of hydrogen plasma etching and RF power, the properties of as-prepared flexible graphene on glass are modulated to be able to achieve the graphene's transparency, good electrical conductivity, and better macroscopic uniformity. Direct growth of graphene film without any metal catalyst on flexible glass can be a promising candidate for applications in flexible transparent optoelectronics. [ABSTRACT FROM AUTHOR]

Starting from the Davey–Stewartson equation, a Boussinesq-type coupled equation system is obtained by using a variable separation approach. For the Boussinesq-type coupled equation system, its consistent Riccati expansion (CRE) solvability is studied with the help of a Riccati equation. It is significant that the soliton–cnoidal wave interaction solution, expressed explicitly by Jacobi elliptic functions and the third type of incomplete elliptic integral, of the system is also given. [ABSTRACT FROM AUTHOR]

In vapour deposition, single atoms (adatoms) on the substrate surface are the main source of growth. The change in its density plays a decisive role in the growth of thin films and quantum size islands. In the nucleation and cluster coalescence stages of vapour deposition, the growth of stable clusters occurs on the substrate surface covered by stable clusters. Nucleation occurs in the non-covered part, while the total area covered by stable clusters on the substrate surface will gradually increase. Carefully taking into account the coverage effect, a revised single atom density rate equation is given for the famous and widely used thin-film rate equation theory, but the work of solving the revised equation has not been done. In this paper, we solve the equation and obtain the single-atom density and capture number by using a uniform depletion approximation. We determine that the single atom density is much lower than that evaluated from the single atom density rate equation in the traditional rate equation theory when the stable cluster coverage fraction is large, and it goes down very fast with an increase in the coverage fraction. The revised equation gives a higher value for the 'average' capture number than the present equation. It also increases with increasing coverage. That makes the preparation of single crystalline thin film materials difficult and the size control of quantum size islands complicated. We also discuss the effect of the revision on coalescence and the number of stable clusters in vapour deposition. [ABSTRACT FROM AUTHOR]

Introducing deep traps by grafting functional groups on molecular chains of polymeric dielectric materials has been proved as an effective way to improve their electrical properties, especially suppressing the space charge injection and accumulation. However, the underlying physical mechanism of the origins and effects of deep traps on the electrical properties of polymeric dielectrics has not been fully understood. In order to explore the origins and effects of deep traps in grafted polymers, both simulations of electronic band structures as well as 3D electric potential distributions at molecular level and experiments on the macroscopic trap level distributions are carried out. The simulation and experiment results reveal that the deep traps in grafted polymers originate from the different electronic band structures of the grafted polymer compared with the pristine polymer. The deep traps would capture charge carriers and inhibit the charge transport, which leads to decreased conduction current and suppressed space charge injection and accumulation. This work provides a deep understanding of the origins of deep traps in grafted polymers and their effects on the electrical properties, which may guide the rational design of high-performance polymeric dielectric and insulation materials. [ABSTRACT FROM AUTHOR]

The prospect of α-Ga2O3 in optical and electrical devices application is fascinating. In order to obtain better performance, Ge and F elements with similar electronegativity and atomic size are selected as dopants. Based on density functional theory (DFT), we systematically research the electronic structure and optical properties of doped α-Ga2O3 by GGA+U calculation method. The results show that Ge atoms and F atoms are effective n-type dopants. For Ge-doped α-Ga2O3, it is probably obtained under O-poor conditions. However, for F-doped α-Ga2O3, it is probably obtained under O-rich conditions. The doping system of F element is more stable due to the lower formation energy. In this investigation, it is found that two kinds of doping can reduce the α-Ga2O3 band gap and improve the conductivity. What is more, it is observed that the absorption edge after doping has a blue shift and causes certain absorption effect on the visible region. Through the whole scale of comparison, Ge doping is more suitable for the application of transmittance materials, yet F doping is more appropriate for the application of deep ultraviolet devices. We expect that our research can provide guidance and reference for preparation of α-Ga2O3 thin films and photoelectric devices. [ABSTRACT FROM AUTHOR]

Reducing the contact resistance without degrading the mobility property is crucial to achieve high-performance graphene field effect transistors. Also, the idea of modifying the graphene surface by etching away the deposited metal provides a new angle to achieve this goal. We exploit this idea by providing a new process method which reduces the contact resistance from 597 Ω·μm to sub 200 Ω·μm while no degradation of mobility is observed in the devices. This simple process method avoids the drawbacks of uncontrollability, ineffectiveness, and trade-off with mobility which often exist in the previously proposed methods. [ABSTRACT FROM AUTHOR]

Grain boundary activity in nanocrystalline Al under an indenter is studied by using a multiscale method. It is found that grain boundaries and twin boundaries can be transformed into each other by emitting and absorbing dislocations. The transition processes might result in grain coarsening and refinement events. Dislocation reflection generated by a piece of stable grain boundary is also observed, because of the complex local atomic structure within the nanocrystalline Al. This implies that nanocrystalline metals might improve their internal structural stability with the help of some special local grain boundaries. [ABSTRACT FROM AUTHOR]

A separate absorption, grading, charge and multiplication InGaAs/InP avalanche photodiode with ultra low dark current and high responsivity is demonstrated. It has a thin multiplication layer and a planar structure. Through the use of a well and a single floating guard ring to suppress edge breakdown, the device can easily be fabricated by one step epitaxial growth and one step diffusion. The dark current of a 30 μm diameter device is as low as 0.028 nA at punch-through and 0.1 nA at 90% of the breakdown voltage. The responsivity at 1.55 μm is 0.93A/W at unity gain and the multiplication layer is estimated to be less than 300 nm. [ABSTRACT FROM AUTHOR]

We demonstrate a simple scheme of 6.835 GHz microwave source based on the sub-sampling phase lock loop (PLL). A dielectric resonant oscillator of 6.8 GHz is directly phase locked to an ultra-low phase noise 100 MHz oven controlled crystal oscillator (OCXO) utilizing the sub-sampling PLL. Then the 6.8 GHz is mixed with 35 MHz from an direct digital synthesizer (DDS) which is also referenced to the 100 MHZ OCXO to generate the final 6.835 GHz signal. Benefiting from the sub-sampling PLL, the processes of frequency multiplication, which are usually necessary in the development of a microwave source, are greatly simplified. The architecture of the microwave source is pretty simple. Correspondingly, its power consumption and cost are low. The absolute phase noises of the 6.835 GHz output signal are −47 dBc/Hz, −77 dBc/Hz, −104 dBc/Hz and −121 dBc/Hz at 1 Hz, 10 Hz, 100 Hz and 1 kHz offset frequencies, respectively. The frequency stability limited by the phase noise through the Dick effect is theoretically estimated to be better than 5.0 × 10−14τ1/2 when it is used as the local oscillator of the Rb atomic clocks. This low phase noise microwave source can also be used in other experiments of precision measurement physics. [ABSTRACT FROM AUTHOR]