Silicon V-groove Research Articles

High-quality germanium growth on (111)-faceted V-groove silicon by molecular beam epitaxy

High-quality and low-defect-density germanium (Ge) buffer layers on silicon (Si) substrates have long been developed for group IV and III–V devices by suppressing defect propagation during epitaxial growth. This is a crucial step for the development of highly efficient photonic devices on Si substrates. Patterned silicon substrates have increasingly been employed for their ability to restrict and hinder the motion of defects. In this work, we demonstrate the effectiveness of an optimised two-step growth recipe structure on a (111)-faceted V-groove silicon substrate with a 350 nm flat ridge. This strategy successfully reduces the threading dislocation (TD) density while growing a 1 μm Ge buffer layer via molecular beam epitaxy. As a result, a high-quality buffer is produced with a low TD density on the order of 107 cm−2 and a surface roughness below 1 nm.

Enhancing and confining light in hybrid plasmonic nanowire-integrated V-groove silicon waveguides

In recent years, the field of dielectric-plasmonic photonics has made remarkable strides, leading to the successful development of various technologies. The realization of sophisticated optical circuits on a single platform has become increasingly viable. Here we propose and investigate a hybrid dielectric waveguide integrated with plasmonics. This hybrid optical waveguide comprises a copper nanowire situated in close proximity to a silicon V-groove channel, separated by a nanoscale gap. This configuration is particularly advantageous, as achieving precise alignment of the nanowire within the V-groove addresses a fundamental challenge in engineering a fully functional integrated component. Additionally, a silicon nitride film coats the V-groove. Utilizing finite element analysis, we conduct numerical simulations to analyze field properties and modal propagation at a specific wavelength of 1550 nm. Our simulations reveal that meticulous optimization of the nanowire and V-groove channel’s geometrical parameters enables effective tailoring of the hybrid mode. This optimization results in strong mode coupling between the dielectric waveguide mode and the surface plasmon, leading to substantial field enhancement, confinement, and extended propagation length. These waveguides also hold promise for sensing applications, facilitating the detection of sample variations and locations due to pronounced mode characteristics. The proposed hybrid approach demonstrates potential for integration into high-level photonic circuits and on-chip optical computing systems.

Pyramidal shape four V-grooved silicon substrate for enhancing cubic phase gallium nitride growth

Strong spontaneous polarization and piezoelectric effects in hexagonal gallium nitride (h-GaN) seriously limit the efficiency of h-GaN-based devices. To overcome this issue, a pyramidal-shaped four V-grooved silicon (4PVG-Si) patterned substrate is introduced for transforming h-GaN into cubic GaN (c-GaN) at the nanoscale. The purpose of using 4PVG-Si instead of simple V-grooved Si (VG-Si) is to improve the crystal quality with the maximum cubic volume of GaN. The growth of c-GaN was verified by high-resolution x-ray diffraction and cathodoluminescence, whereas high-resolution transmission electron microscopy (HRTEM) was further used to analyze the excessive and smooth c-GaN growth. The HRTEM images revealed that optimizing the growth of an aluminum nitride layer with 10–15 nm thicknesses promotes the maximum c-GaN volume. However, exceeding this thickness tended to the reduction in c-GaN volume, resulting in the development of big voids with abnormal tip-shaped growth. In the presence of big voids and abnormal tip-shaped growth, the hexagonal growth closed very late, and the cubic volume of c-GaN is reduced. To further promote the cubic phase of GaN, the growth conditions of GaN were also optimized. Our results proved that the design of 4PVG-Si and optimized growth conditions promote the maximum cubic volume of GaN.

Broadband omnidirectional anti-reflection property of V-groove textured silicon

Omnidirectional silicon solar cells with an outstanding anti-reflection property over a broad angular range of incident light show great potential for application in the photovoltaic industry. Many studies have been carried out to investigate the omnidirectional anti-reflection properties of different silicon textured structures. However, the omnidirectional anti-reflection property of the V-groove textured silicon has not been reported, even though the V-groove structure is also one of most frequently used anti-reflective structures for silicon solar cells. In this research, ray tracing simulation is utilized to analyze and validate the omnidirectionality of a micron-sized silicon V-groove structure. In addition, in consideration of the previous complicated fabrication methods of V-groove structure, a brand new fabrication method for the V-groove texturization onto diamond-wire-sawn monocrystalline silicon wafers through copper-assisted chemical etching is presented. Consistent with the simulations, the experimental results similarly indicate that the V-groove textured silicon not only possesses light absorption ability that is comparable to the common random pyramid structure but also exhibits an unexpected excellent omnidirectional anti-reflection property over a wide range of incident angles, demonstrating the great potential for the fabrication of omnidirectional silicon solar cells.

Multiscale Modeling of the Three-Dimensional Meniscus Shape of a Wetting Liquid Film on Micro-/Nanostructured Surfaces.

The design of structured surfaces for increasing the heat flux dissipated during boiling and evaporation processes via enhanced liquid rewetting requires prediction of the liquid meniscus shape on these surfaces. In this study, a general continuum model is developed to predict the three-dimensional meniscus shape of liquid films on micro/nanostructured surfaces based on a minimization of the system free energy that includes solid-liquid van der Waals interaction energy, surface energy, and gravitational potential. The continuum model is validated at the nanoscale against molecular dynamics simulations of water films on gold surfaces with pyramidal indentations, and against experimental measurements of water films on silicon V-groove channels at the microscale. The validated model is used to investigate the effect of film thickness and surface structure depth on the meniscus shape. The meniscus is shown to become more conformal with the surface structure as the film thickness decreases and the structure depth increases. Assuming small interface slope and small variation in film thickness, the continuum model can be linearized to obtain an explicit expression for the meniscus shape. The error of this linearized model is quantitatively assessed and shown to increase with increasing structure depth and decreasing structure pitch. The model developed can be used for accurate prediction of three-dimensional meniscus shape on structured surfaces with micro/nano-scale features, which is necessary for determining the liquid delivery rate and heat flux dissipated during thin-film evaporation. The linearized model is useful for rapid prediction of meniscus shape when the structure depth is smaller than or comparable to the liquid film thickness.

Split-Wedge Antennas with Sub-5 nm Gaps for Plasmonic Nanofocusing.

We present a novel plasmonic antenna structure, a split-wedge antenna, created by splitting an ultrasharp metallic wedge with a nanogap perpendicular to its apex. The nanogap can tightly confine gap plasmons and boost the local optical field intensity in and around these opposing metallic wedge tips. This three-dimensional split-wedge antenna integrates the key features of nanogaps and sharp tips, i.e., tight field confinement and three-dimensional nanofocusing, respectively, into a single platform. We fabricate split-wedge antennas with gaps that are as small as 1 nm in width at the wafer scale by combining silicon V-grooves with template stripping and atomic layer lithography. Computer simulations show that the field enhancement and confinement are stronger at the tip–gap interface compared to what standalone tips or nanogaps produce, with electric field amplitude enhancement factors exceeding 50 when near-infrared light is focused on the tip–gap geometry. The resulting nanometric hotspot volume is on the order of λ3/106. Experimentally, Raman enhancement factors exceeding 107 are observed from a 2 nm gap split-wedge antenna, demonstrating its potential for sensing and spectroscopy applications.

Optical properties of V-groove silicon nitride trench waveguides.

We numerically investigate the mode properties of the V-groove silicon nitride trench waveguides based on the experimental results. The trench waveguides are suitable for nonlinear applications. By manipulating the waveguide thicknesses, the waveguides can achieve zero dispersion or a maximized nonlinear parameter of 0.219 W-1·m-1 at 1550 nm. Broadband four-wave mixing with a gain of 5.545 m-1 is presented as an example. The waveguides can also be applied in sensing applications with an optimized evanescent intensity ratio. By etching away the top flat slabs, wider trapezoidal trench waveguides can be utilized for plasmonic sensing thanks to their TE fundamental modes.

Growing InGaAs quasi-quantum wires inside semi-rhombic shaped planar InP nanowires on exact (001) silicon

We report InGaAs quasi-quantum wires embedded in planar InP nanowires grown on (001) silicon emitting in the 1550 nm communication band. An array of highly ordered InP nanowire with semi-rhombic cross-section was obtained in pre-defined silicon V-grooves through selective-area hetero-epitaxy. The 8% lattice mismatch between InP and Si was accommodated by an ultra-thin stacking disordered InP/GaAs nucleation layer. X-ray diffraction and transmission electron microscope characterizations suggest excellent crystalline quality of the nanowires. By exploiting the morphological evolution of the InP and a self-limiting growth process in the V-grooves, we grew embedded InGaAs quantum-wells and quasi-quantum-wires with tunable shape and position. Room temperature analysis reveals substantially improved photoluminescence in the quasi-quantum wires as compared to the quantum-well reference, due to the reduced intrusion defects and enhanced quantum confinement. These results show great promise for integration of III-V based long wavelength nanowire lasers on the well-established (001) Si platform.

Continuous V-Grooved AlGaN/GaN Surfaces for High-Temperature Ultraviolet Photodetectors

Three-dimensional heterostructured AlGaN/GaN ultraviolet (UV) photodetectors were microfabricated using V-grooved silicon(111) surfaces and metal organic chemical vapor deposition. This novel sensor platform enabled an increase in sensitivity and operation at high temperatures (up to 200°C). More specifically, texturizing the highly conductive 2-D electron gas using the V-groove sensor surfaces, resulted in higher photodetector sensitivity (57.4% increase at room temperature and 139% at 200°C) compared with conventional designs on planar substrates due to the increased absorption of incident UV light (optical trapping). In addition, a 53% reduction in electrical resistance at room temperature and 27.3% at 200°C were observed due to the increased surface area. The decay time for the non-exponential persistent photoconductivity decreased significantly from 327 to 34 sec as the temperature increased from room temperature to 200°C as a result of the accelerated electron–hole pair recombination (generation) rate. These results support the use of textured AlGaN/GaN sensor platforms for UV detection in harsh environments (e.g., downhole, combustion, and space).

High-Precision, Self-Aligned, Optical Fiber Connectivity Solution for Single-Mode Waveguides Embedded in Optical PCBs

A fully passive, optical fiber connectivity solution for polymer waveguides embedded in electro-optical printed circuit boards (EOCB) is described and its preliminary results for single-mode applications demonstrated. The connectivity solution is based on a pluggable glass-fiber connector interface and a self-alignment packaging technology using high-precision silicon V-grooves. The V-grooves provide precise positioning of the glass-fiber relative to the polymer waveguide through alignment structures on the EOCB, patterned in the same laser direct writing fabrication step as the waveguide core. We realized an EOCB module with an LC-connector pluggable adaptor interface assembled on one side of the EOCB. With this module, we were able to prove for the first time the usability of our connectivity solution for single-mode applications. Coupling losses as low as 1.2 dB between a standard LC-connector and the single-mode polymer waveguide embedded into the EOCB have been reached. This passive packaging solution provides a cost-effective optical connectivity to wave-guides in EOCBs, which will be required in future generations of optical interconnects.

10 Gbps/ch Full-Duplex Optical Link Using a Single-Fiber Channel for Signal Transmission

A 10 Gbps/ch full-duplex (simultaneous bidirectional) optical link utilizing two optical subassembly (OSA) transceiver (TRx) modules and two wavelengths, 850 and 1060 nm, for sending and receiving optical signals through a single fiber channel in a fiber array is demonstrated. Each of the OSA TRx modules consists of transmitter/receiver chips, optical fibers embedded in a V-grooved silicon substrate, two 45 ° mirrors formed in fibers, and three silicon optical benches for mounting vertical-cavity surface-emitting lasers, photodiodes (PDs), and monitoring PDs. Mirror-1 in the fiber is coated with a wavelength-filtering layer to reflect transmitted light and pass through received light. Mirror-2 deflects received light to the PD. Two OSA TRx modules were applied in an end-to-end quad small form-factor pluggable optical link for 40-Gbps operation. This optical link showed good performance with clear eye-diagrams and a BER of at <;10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> Gbps/ch with -8-dBm input power.

40 Gb/s optical subassembly module for a multi-channel bidirectional optical link

A 40 Gb/s bidirectional optical link using four-channel optical subassembly (OSA) modules and two different wavelengths for the up- and down-link is demonstrated. Widely separated wavelengths of 850 nm and 1060 nm are used to reduce the optical crosstalk between the up- and down-link signals. Due to the integration capabilities of silicon, the OSA is implemented, all based on silicon: V-grooved silicon substrates to embed fibers and silicon optical benches (SiOBs) to mount optical components. The SiOBs are separately prepared for array chips of photodiodes (PDs), vertical-cavity surface-emitting lasers (VCSELs), and monitoring PDs, which are serially configured on an optical fiber array for direct coupling to the transmission fibers. The separation of the up- and down-link wavelengths is implemented using a wavelength-filtering 45° mirror which is formed in the fiber under the VCSEL. To guide the light signal to the PD another 45° mirror is formed at the end of the fiber. The fabricated bidirectional OSA module shows good performances with a clear eye-diagram and a BER of less than 10(-12) at a data rate of 10 Gb/s for each of the channels with input powers of -8 dBm and -6.5 dBm for the up-link and the down-link, respectively. The measured inter-channel crosstalk of the bidirectional 40 Gb/s optical link is about -22.6 dB, while the full-duplex operation mode demonstrates negligible crosstalk between the up- and down-link.

Biwavelength transceiver module for parallel simultaneous bidirectional optical interconnections

The design of a biwavelength transceiver (TRx) module for parallel simultaneous bidirectional optical interconnects is described. The TRx module has been implemented using two different wavelengths, 850 and 1060 nm, to send and receive signals simultaneously through a common optical interface while optimizing cost and performance. Filtering mirrors are formed in the optical fibers which are embedded on a V-grooved silicon substrate for reflecting and filtering optical signals from/to vertical-cavity surface-emitting laser (VCSEL)/photodiode (PD). The VCSEL and PD are flip-chip bonded on individual silicon optical benches, which are attached on the silicon substrate for optical signal coupling from the VCSEL to fiber and from fiber to the PD. A high-speed and low-loss ceramic printed circuit board, which has a compact size of 0.033 cc, has been designed to carry transmitter and receiver chips for easy packaging of the TRx module. Applied for quad small form-factor pluggable applications at 40-Gbps operation, the four-channel biwavelength TRx module showed clear eye diagrams with a bit error rate (BER) of 10 −12 at input powers of −5 and −5.8 dBm for 1060 and 850 nm operation modes, respectively.

A single-walled carbon nanotube thin film solar microcell with V-groove array structure

This article reports an exploratory single-walled carbon nanotube thin film solar microcell with V-groove array structure on Si (100) substrate. Single-walled carbon nanotube thin film–Si heterojunction serves as energy conversion part in solar microcells, including electron–hole pair generation, carrier collection and transportation. V-groove was designed and prepared on silicon substrate by KOH anisotropic wet-etching for improving the performance of solar microcell. Simple solution–evaporation method was used to achieve conformal single-walled carbon nanotube thin film on V-groove silicon substrate. Under 100 mW/cm2 solar illumination, our solar microcell with V-groove arrays shows open-circuit voltage (VOC) of 195 mV, short-circuit current density (JSC) of 4.76 µA/cm2 and fill factor of 24.8%. The VOC and JSC are, respectively, enhanced by 387.5% and 217.3% compared to the microcell without V-groove arrays. It is proved that the V-groove structure can improve the performance of single-walled carbon nanotube thin film solar microcell.

Investigation on Silicon V-Grooves Measurement with Spectral Domain Optical Coherence Tomography (SDOCT)

The objective of this research was to investigate a new detection method for testing a MEMS V-shaped groove in silicon using spectral domain optical coherence tomography (SDOCT) technique with a thermal light source where the V-groove depth, width and bottom width were measured. The SD-OCT technique with non-contact operation and acquisition rate advantage made it suitable for on-line precision measurement of V-shaped grooves in silicon.

Taper-free and kinked germanium nanowires grown on silicon via purging and the two-temperature process

We investigate the growth procedures for achieving taper-free and kinked germanium nanowires epitaxially grown on silicon substrates by chemical vapor deposition. Singly and multiply kinked germanium nanowires consisting of 〈111〉 segments were formed by employing a reactant gas purging process. Unlike non-epitaxial kinked nanowires, a two-temperature process is necessary to maintain the taper-free nature of segments in our kinked germanium nanowires on silicon. As an application, nanobridges formed between (111) side walls of V-grooved (100) silicon substrates have been demonstrated.

A high-performance micro electret power generator based on microball bearings

In this paper, a high-performance micro electret power generator fabricated by simple bulk micromachining technology is presented. It has microballs as movable bearings for harvesting changing low-frequency vibration energy from the environment. The silicon V-grooves where the microballs slide have very smooth (1 1 1) planes, and so the device is sensitive to very slight vibration and almost has no resonant frequency. A plasma-enhanced chemical vapour deposition SiO2/Si3N4 double layer was used as the electret. The device was fabricated by simple micromachining technology suitable for mass production except for microball assembly. The influence of various frequencies and accelerations on the performance was studied in detail. The measurement results of this electret micro power generator show that the optimal load is proportional to the frequency, and inversely proportional to the acceleration. The peak-to-peak output charge and output power were 72 nC and 5.9 µW respectively at 20 Hz and 0.7 g with the optimal resistive load 626 kΩ. The work frequencies range from 100 Hz to a lower frequency (1 Hz). 112 nW can still be obtained in the minimum acceleration of 0.05 g at 10 Hz with the optimal resistive load, indicating that this device has high sensitivity. The possible application of our device in scavenging energy from low-frequency irregular movements, such as human motion, was proved by a primary experiment.

Coefficient of restitution for bouncing nanoparticles

We demonstrate the measurement of the coefficient of restitution, $e$, for nanoparticles, through observations of the final distribution of bismuth particles that have bounced within silicon V-grooves. The experiments, taken together with complementary molecular-dynamics simulations, show that $e$ is generally smaller for liquid than for solid nanoparticles, and that macroscopic theories underestimate the velocity dependence of $e$. Hence, while nanoparticles are harder than bulk materials, once they have begun to yield the rate of increase of the inelastic deformation is greater.

Electrically tunable bandpass filter using solid-core photonic crystal fibers filled with multiple liquid crystals

An electrically tunable bandpass filter is designed and fabricated by integrating two solid-core photonic crystal fibers filled with different liquid crystals in a double silicon v-groove assembly. By separately controlling the driving voltage of each liquid-crystal-filled section, both the short-wavelength edge and the long-wavelength edge of the bandpass filter are tuned individually or simultaneously with the response time in the millisecond range.

Measurement of Steep Surfaces Using White Light Interferometry

Abstract: Scanning white light interferometry (SWLI) is an increasingly popular method to measure the surface profile of miniature components. Although it is tolerant to step changes in profile, its capability to measure the large surface gradients that are characteristic of high-aspect-ratio surfaces is limited. This is in part due to the numerical aperture of the objective lens which restricts the spatial frequency content of both the illumination and recorded fields. More fundamentally, though, SWLI instrumentation neglects the effects of multiple scattering and assumes that the field which illuminates the object is that which would be present if the object were absent. Although this is a reasonable approximation for slowly varying surfaces, it is generally not true for those with steep gradients. In this paper the 3D theory of SWLI is presented and the approximations made by current instrumentation are discussed in this context. Using finite element methods (FEM), SWLI interferograms are calculated, for the cases of 2D Silicon V-grooves and step artefacts, and the effects of multiple scattering are illustrated. Methods to improve the capability of SWLI to measure large surface gradients, first by tilting the sample and subsequently by using an iterative FEM model to provide improved estimates of the illuminating conditions are introduced.