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Precision prediction of machined surface roughness is challenging facing the robotic belt grinding of complex blade, since this process is accompanied by significant elastic deformation. The resulting poor prediction accuracy, to a great extent, is attributed to the existing prediction model which less considers the dynamics. In this paper, an improved scallop height model is developed to predict and assess the machined surface roughness by taking into account the elastic deformation and the varying curvature of blade, then robotic belt grinding experiments are carried out to evaluate the proposed model from the perspective of surface roughness. Finally factors that influence the scallop height are analyzed, and the suitable empirical equation of surface roughness is proposed to assess and predict the surface quality from the aspect of blade concave and convex surface by adopting the constant scallop height machining.

In recent decades, dual-band photodetectors have received widespread attention due to better target identification, which are considered as the development trend of next generation photodetectors. However, the traditional dual-band photodetectors based on heteroepitaxial growth, superlattice and multiple quantum well structures are limited by complex fabrication process and low integration. Herein, we report a UV/IR dual-band photodetector by integrating ultra-wide gap β-Ga2O3 and narrow-gap black phosphorous(BP) nanoflakes. A vertical van der Waals (vdW) heterostructure is formed between BP and β-Ga2O3 by mechanically exfoliated method integrated without the requirement of lattice match. The heterostructure devices show excellent rectification characteristics with high rectifying ratio of ca. 106 and low reverse current around pA. Moreover, the device displays obvious photoresponse under UV and IR irradiations with responsivities of 0.87 and 2.15 mA/W, respectively. We also explore the band alignment transit within the heterostructure photodetector at different bias voltages. This work paves the way for fabricating novel dual-band photodetectors by utilizing 2D materials.

The elastic state at contact wheel–workpiece interface is a critical issue during robotic belt grinding process that significantly influences the finishing profile accuracy. Establishing a reasonable undeformed chip-thickness (UCT) model that suits to this operation is considered a feasible approach to clarify the cutting mechanisms. In the present paper, an elastic state–driven robotic belt grinding chip-thickness model is established to predict the workpiece surface roughness. In this new model, the combined modulus of elasticity of the contact wheel is calculated according to the formula of Young’s modulus, and the exponent with respect to the effects of linear and nonlinear deflection is further determined based on the energy balance hypothesis. Experiments are conducted to verify the reasonability of the improved chip-thickness model from the perspective of surface roughness, and the findings are likely to clarify the differences in material removal mechanism between wheel grinding and robotic belt grinding essentially.

A tentative study from the perspective of abrasive grain geometry in this paper is conducted to investigate the specific energy and energy efficiency for clarifying the robotic belt grinding mechanisms. The energy efficiency model is established based on the friction coefficient model of the single spherical grain, then the experiments and simulation are implemented to energetically evaluate the microscale material removal mechanisms from the specific energy contributions. It has been demonstrated that the specific plowing energy is more predominant than both the specific cutting and sliding energy in robotic belt grinding, resulting in the energy efficiency ranges between 17 and 41 %. Both the large grain size and normal contact force can be taken as optimization strategies to maximize the energy efficiency for material removal.

We demonstrate a structure design of electrically pumped 1.3 μm InAs/InGaAs quantum dot microdisk lasers on silicon with an output waveguide . Three-dimensional finite-difference time-domain method is used to numerically analyze the mode characteristics of the microdisk lasers. The effects of the diameter of microdisk cavity, the thickness of cladding layer, the etching depth and the waveguide width on the quality factor (Q-factor) are studied in detail. The results show that when the microdisk laser with a diameter of 7 μm, a thickness of cladding layer of 1.75 μm, an etching depth of 4.53 μm and a waveguide width of 0.5 μm, the Q-factor is maximized. The mode wavelength and the mode quality factor are 1304.45 nm and 19133, respectively. The photoelectric properties of InAs/InGaAs quantum dot microdisk lasers are simulated by rate equations.

We propose and numerically analyze a broadband and high extinction ratio mode converter to achieve the mode conversion between the fundamental transverse electric mode (TE0) and the first-order transverse magnetic mode (TM1). The mode converter is achieved by using the tapered hybrid plasmonic waveguide which the metal is directly covered on the Si waveguide without a thin low-index layer. After optimizing the structure of the tapered hybrid plasmonic waveguide, a wide operation bandwidth of 100 nm is obtained with the extinction ratio of the TM1 mode and TE0 mode larger than 20 dB in the output Si waveguide for the forward propagation. And for the back propagation, the operation bandwidth over 65 nm is obtained with the extinction ratio larger than 20 dB in the output Si waveguide. The whole footprint of the mode converter is only 0.8 × 11 μm2. Fabrication tolerance analysis is also demonstrated.

We report a structure design of 1.55 μm square microcavity lasers monolithically integrated on GaAs substrates. The mode characteristics of the microcavity lasers are numerically investigated by three-dimensional finite-difference time-domain method. The dependences of the high-quality factor modes on the side length of the microcavity, the width of the output waveguide and the etching depth are investigated in detail. The results demonstrate, for the microcavity structure with the side length of 12 μm, the output waveguide width of 1.0 μm and the etching depth of 3.55 μm, it is optimal to excite high-quality factor modes around wavelength of 1.55 μm. The mode wavelength and the mode quality factor are 1547.46 nm and 2416.28, respectively. The quality factor degrades rapidly with the waveguide width increasing, and increases with increasing etching depth.

Epitaxial lateral overgrowth (ELO) of 1.8-μm InP films was performed on nanopatterned GaAs (001) substrates via metal–organic chemical vapor deposition. Parallel SiO2 trenches with a nano-scale width (∼ 170 nm) and various seed line orientations of [110], [410], [010] and [4–10] were first adopted to optimize the growth in our work. Scanning electron microscopy, atomic force microscopy and double-crystal x-ray diffraction were used to characterize the as-grown InP/GaAs heterostructures. The results reveal that the surface morphology and crystalline quality are strongly affected by the seed line orientations, and both of these parameters are optimized under the orientation of the [4–10] direction. A low average full width at half maximum of 285.1 arcsec and a root mean square surface roughness of 2.95 nm are obtained for the 1.8-μm InP film. To clearly observe the initial coalescence stage during the growth processes, thinner (500 nm) ELO InP films were also grown. We found that the seed line orientation has a significant effect on the lateral growth rate and affects the quality of the final InP/GaAs epilayer.

We, first, demonstrate an optimized structure design and analyze the optical mode properties of 1.3 μm wavelength square microcavity lasers on silicon with InAs/InGaAs quantum-dot active region and mid-point output waveguides. Si-based square microcavities with whispering-gallery-like modes have been proposed for optimizing their quality factors (Q factors). Three-dimensional finite-difference time-domain method is used to numerically analyze the optical mode characteristics. The influences of the side-length of the microcavity, the output waveguide width, and the etching depth on the optical modes of the microcavity are investigated in detail. It indicates that the Q factor increases with increasing etching depth, and decreases rapidly as the waveguide width increases. The results show that with the side length of 18 μm, the waveguide width of 1.0 μm, and the etching depth of 3.5 μm, the Q factor is the highest, and the mode distribution is optimal. The mode wavelength and Q factor are 1305.9 nm and 4694.8, respectively. Advantages of more stable and evenly distributed mode profiles for Si-based square microcavity lasers have been demonstrated, and compared with the Si-based disk microcavity (microdisk) lasers. It promises a potential alternative laser structure for Si-based optoelectronic integration.

Comprehensive study of the microscopic material removal mechanism remains an open challenge facing the robotic belt grinding of complex geometries. In the present paper, a new material removal rate (MRR) model is developed underlying the motion trajectory of single spherical abrasive grain by taking into consideration the elastic deformation of the heterogeneous contact wheel. In this model, the contact pressure distribution at the contact wheel–workpiece interface is determined by converting the three-dimensional contact problem into a one-dimensional linear spring model with respect to the large deformation of the contact wheel. In addition, the combined modulus and Poisson's ratio of the heterogeneous contact wheel are further considered based on the geometric relation of the Young's modulus and Poisson's ratio. Compared with the existing MRR model, the proposed MRR model can significantly reduce both the root mean square error (RMSE) and mean absolute percentage error (MAPE) values from 2.401 to 1.725, and 18.426% to 14.942%, respectively. Particularly, an optimization strategy from the perspective of process parameters is implemented to balance the grinding quality and efficiency.

We investigate the thermal stresses for GaAs layers grown on V-groove patterned Si substrates by the finite-element method. The results show that the thermal stress distribution near the interface in a patterned substrate is nonuniform, which is far different from that in a planar substrate. Comparing with the planar substrate, the thermal stress is significantly reduced for the GaAs layer on the patterned substrate. The effects of the width of the V-groove, the thickness, and the width of the SiO2 mask on the thermal stress are studied. It is found that the SiO2 mask and V-groove play a crucial role in the stress of the GaAs layer on Si substrate. The results indicate that when the width of V-groove is 50 nm, the width and the thickness of the SiO2 mask are both 100 nm, the GaAs layer is subjected to the minimum stress. Furthermore, Comparing with the planar substrate, the average stress of the GaAs epitaxial layer in the growth window region of the patterned substrate is reduced by 90%. These findings are useful in the optimal designing of growing high-quality GaAs films on patterned Si substrates.

Black phosphorous (BP), an excellent two-dimensional (2D) monoelemental layered p-type semiconductor material with high carrier mobility and thickness-dependent tunable direct bandgap structure, has been widely applied in various devices. As the essential building blocks for modern electronic and optoelectronic devices, high quality PN junctions based on semiconductors have attracted widespread attention. Herein, we report a junction field-effect transistor (JFET) by integrating narrow-gap p-type BP and ultra-wide gap n-type β-Ga2O3 nanoflakes for the first time. BP and β-Ga2O3 form a vertical van der Waals (vdW) heterostructure by mechanically exfoliated method. The BP/β-Ga2O3 vdW heterostructure exhibits remarkable PN diode rectifying characteristics with a high rectifying ratio about 107 and a low reverse current around pA. More interestingly, by using the BP as the gate and β-Ga2O3 as the channel, the BP/β-Ga2O3 JFET devices demonstrate excellent n-channel JFET characteristics with the on/off ratio as high as 107, gate leakage current around as low as pA, maximum transconductance (g m) up to 25.3 µS and saturation drain current (I DSS) of 16.5 µA/µm. Moreover, it has a pinch-off voltage of –20 V and a minimum subthreshold swing of 260 mV/dec. These excellent n-channel JFET characteristics will expand the application of BP in future nanoelectronic devices.

We design two types of output waveguide structures based on bus waveguide: waveguide overlapping with microdisk cavity and single-ended output bus waveguide. This is the first time that these two output structures have been designed for microdisk lasers on silicon. Three-dimensional finite-difference time-domain method is used to numerically analyze the optical mode characteristics of the microdisk lasers. The quality factor (Q-factor) and optical mode distribution of microdisk lasers are calculated in detail. The photoelectric properties of microdisk lasers with different output structures are simulated by rate equations, which provide evidence for lasing. For the first time, by comparing the differences between the two output structures, we identify the respective characteristics of these two structures: microdisk lasers with the waveguide overlaps with the microdisk cavity are suitable for vertical coupling devices when the notch width is 3.5 μm and the waveguide width is 1.5 μm. And the single-ended bus waveguide output structure changes the bus waveguide structure from two-ended to single-ended, which meets the requirement of laser directional output.

A polarization beam splitter is proposed using silicon-nitride-assisted three-waveguide couplers. With 7 μm coupling length, the extinction ratios are more than 30 dB and insertion losses are less than 0.15 dB at 1.55 μm wavelength.

In this work, a technique for the growth of GaAs epilayers on Si, combining an ultrathin amorphous Si buffer layer and a three-step growth method, has been developed to achieve high crystalline quality for monolithic integration. The influences of the combined technique for the crystalline quality of GaAs on Si are researched in this article. The crystalline quality of GaAs epilayer on Si with the combined technique is investigated by scanning electron microscopy, double crystal X-ray diffraction (DCXRD), photoluminescence, and transmission electron microscopy measurements. By means of this technique, a 1.8-µm-thick high-quality GaAs/Si epilayer was grown by metal–organic chemical vapor deposition. The full-width at half-maximum of the DCXRD rocking curve in the (400) reflection obtained from the GaAs/Si epilayers is about 163 arcsec. Compared with only using three-step growth method, the current technique reduces etch pit density from 3 × 106 cm−2 to 1.5 × 105 cm−2. The results demonstrate that the combined technique is an effective approach for reducing dislocation density in GaAs epilayers on Si.

The GaAsP/Si dual-junction solar cells have been systematically investigated in our paper by using AMPS (Analysis of Microelectronic and Photonic Structures). Based on the optimized results of single-junction solar cells, we propose a promising method to improve the properties of the dual-junction solar cell. And the monolithic GaAs x P 1−x /Si dual-junction solar cells with various As compositions (x=0.65, 0.75, 0.85) and base thicknesses (t b =0.05∼2.5um) were analyzed. The remarkable conversion efficiency of 35.8% has been obtained for the GaAs 0.75 P 0.25 /Si dual-junction solar cells, which is higher than previously reported results. Our method and results will provide a significant guidance for the design and manufacture of Si-based dual-junction solar cells.

We report a 1.55μΜ square microcavity laser monolithically integrated on GaAs substrates. The mode characteristics of the microcavity laser are numerically investigated by three-dimensional finite difference time domain method. The dependences of the whispering-gallery modes on the width of the output waveguide and the etching depth are discussed. For the cavity with the side length of 12μm and the output waveguide of 1μm, it is easy to excite whispering-gallery modes around 1.55μm. The mode wavelength is 1542.88nm and the mode Q factor is 2389.23. The Q factor degrades rapidly with the waveguide width increasing and increases with the increasing of the etching depth.

We demonstrate firstly an optimized InAs/InGaAs quantum-dot microdisk laser structure on silicon. The simulations indicate that Q-factor can exceed 106 at wavelength of with the diameter and the cladding layer thickness of 7μm and 1.75μm.

We have designed three mode order converters using the sub-wavelength grating on the silicon-on-insulator substrate. The proposed mode order converters can separately realize the mode order conversion from the fundamental transverse electric mode to the first-order transverse electric mode (TE0-to-TE1), the second-order transverse electric mode (TE0-to-TE2) and the third-order transverse electric mode (TE0-to-TE3) with compact device sizes and good performances. The simulation results show that the mode order conversion efficiencies of TE0-to-TE1, TE0-to-TE2 and TE0-to-TE3 are larger than 94.4%, 95.7% and 83.7% in the wavelength ranging from 1.5 µm to 1.6 µm, the corresponding device length are 8.72 µm, 4.98 µm and 14.54 µm. In addition, the mode order converter can be fabricated with only once etching which will be advantage to the device fabrication.

A black arsenic-phosphorus saturable absorber (SA) was fabricated and experimentally applied for a passively Q-switched Er-doped fiber laser for the first time to the best of our knowledge. The high-quality black arsenic-phosphorus crystals were synthesized by the mineralizer-assisted chemical vapor transport (CVT) method, and the fewer-layer black arsenic-phosphorus thin film nanosheet SA was performed by a unique electrochemical delamination exfoliation procedure. Meanwhile, a stable passively Q-switched pulse was proposed based on the SA modified Er-doped ring fiber cavity, which had the repetition rate of 38.47 kHz, corresponding to a minimum pulse width of 5.26 µs, and a corresponding output power as high as 3.68 mW was obtained. The results suggest that black arsenic-phosphorus is a good choice to make practical two-dimensional saturable absorbers for potential ultrafast photonic applications due to its designable bandgap value and excellent optical characteristics.

In this article, anti-reflection coatings (ARCs) with double-layer metal nanoparticles for Cu(In, Ga)Se2 (CIGS) solar cells were proposed. A study of three ARCs nanostructures (Ag-SiO2-Ag, Au-SiO2-Au and Au-SiO2-Ag structures) on CIGS solar cells was presented using the finite-difference time-domain method. Various ARC nanostructures with different metals (Au and Ag), metal nanoparticle radius, spacing layer (SiO2) thickness, and period (corresponding to the particle density) on CIGS solar cells were optimized in detail. The Au-SiO2-Ag structure was demonstrated to have a better anti-reflection ability when the thickness of the SiO2 layer is 45 nm, the radius of the metal particle is 14 nm, and the side length of the period is 41 nm. The results demonstrated that the reflectivity of the CIGS solar cells with the optimal ARCs structure was reduce by 83% compared with the case of no ARCs. And compared with the MgF2 anti-reflection film, the reflectivity was reduced by 37%.

The thermal stress due to the thermal expansion mismatch could induce crystallographic defects such as buckling and cracking and degrade device performance. In this paper, the thermal stress distribution in a laser array structure selectively grown on V-groove-patterned Si substrates was investigated by two-dimension finite-element method. Surprisingly, unexpected results are observed that the top of the InGaAs active layer and the most region of the InP cap layer are in compression, which is far different from the thermal stress distribution in planar structures. Two mechanisms have been proposed and modeled to explain the difference—(i) the width of uncoalesced layers is smaller than that of the Si substrate, which causes thermal stress to change in epitaxial layers, and (ii) thermal stress in the InGaAs and InP layers is affected by the V-groove structure. The results show that whether or not the epitaxial layers are coalesced has significant effect on the thermal stress distribution. The effect of the height of the V-groove, the height and the width of the SiO2 mask on the thermal stress distribution was also studied. It is found that the height of V-groove and the height of SiO2 mask play a critical role in the stress distribution. These findings are useful for the optimal designs for the laser array and provide an important step towards the realization of photonic integration circuits on silicon.The thermal stress due to the thermal expansion mismatch could induce crystallographic defects such as buckling and cracking and degrade device performance. In this paper, the thermal stress distribution in a laser array structure selectively grown on V-groove-patterned Si substrates was investigated by two-dimension finite-element method. Surprisingly, unexpected results are observed that the top of the InGaAs active layer and the most region of the InP cap layer are in compression, which is far different from the thermal stress distribution in planar structures. Two mechanisms have been proposed and modeled to explain the difference—(i) the width of uncoalesced layers is smaller than that of the Si substrate, which causes thermal stress to change in epitaxial layers, and (ii) thermal stress in the InGaAs and InP layers is affected by the V-groove structure. The results show that whether or not the epitaxial layers are coalesced has significant effect on the thermal stress distribution. The effect of the...

A 1.55 µm nanoscale laser array is proposed and designed on v-groove patterned Si (0 0 1) substrates. The laser array is designed by taking full advantage of the periodic groove structures of the patterned substrates. The periodic groove structures separated by a SiO2 mask can effectively reduce threading dislocation density in the active region and provide a strong lateral optical confinement for the laser array structure. The optical mode distributions of the single laser are investigated in detail, and the optical confinement factor is calculated to optimize the structure parameters of the laser array. An optimal value of 9.3% for the optical confinement factor is obtained. The analysis of threshold conditions shows that the laser array can achieve lasing with a cavity length of about 1 mm for an internal loss of 40 cm−1.