GaP Substrates Research Articles

Enhancing the performance of graphene and LCP 1x2 rectangular microstrip antenna arrays for terahertz applications using photonic band gap structures

The terahertz (THz) frequency band (0.1–10 THz) has drawn a lot of attention due to the growing demand for greater resolutions, lower latency, faster data rates, and wider bandwidth in 6 G technologies. This range provides data speeds exceeding tens of gigabits per second, large bandwidth, great spectral resolution, and non-ionizing characteristics. THz signals have potential; however they are affected by attenuation, route losses, and atmospheric conditions, necessitating the use of specialised antenna designs. This work presents a 300 GHz rectangular microstrip patch antenna with Graphene as the patch material and Liquid Crystal Polymer (LCP) as the substrate. Photonic band gap (PBG) substrates are used to incorporate cuboid and cylindrical air gaps in square and triangular lattices, hence improving performance. The highest performance is found with cylindrical air gaps in a triangular lattice PBG substrate, which has a bandwidth of 29.56 GHz, a return loss of –48.12 dB, a gain of 10.4 dBi, a directivity of 10.8 dBi, and a radiation efficiency of 91 %. These results establish the proposed antennas as highly effective for broadband and high-speed THz applications, particularly in 6 G systems like advanced sensing applications, ultra-fast device-to-device (D2D) communications, potential beam steering applications, and non-invasive imaging solutions.

Photoluminescence of GaPNAs/GaP(N) superlattices and bulk GaPN layers on GaP substrates

The addition of a few percent of nitrogen to GaP or GaPAs allows obtaining GaPNAs solid solutions that are lattice-matched to the silicon substrate over a wide range of band gaps, which makes it possible to obtain optoelectronic silicon integrated circuits. However, materials with a small fraction of nitrogen are understudied due to the difficulty in epitaxial growth of quaternary solid solutions with three materials of group V. The purpose of the study was the investigation of the influence of the substrate temperature during the epitaxial growth of dilute nitride materials (GaPN solid solution and GaPNAs/GaP(N) superlattices) on their optical properties, as well as the influence of the growth temperature and superlattice design on the bandgap of the resulting material. It was shown that there is an optimal growth temperature for samples: at temperatures below the optimal, non-radiative recombination at defects predominates, and at a temperature higher than the optimal one, the solid solution of the GaPN layer material decomposes into components with a larger and smaller fraction of nitrogen. Studies were also carried out on the decay of photoluminescence intensity over time in the studied structures at room temperature, which allowed us to evaluate the influence of growth parameters and structure design on the lifetime of nonequilibrium charge carriers. The best lifetime for structures with superlattices was obtained for the GaPNAs/GaPN superlattice and amounted to ~0.2 ns. As a result, the optimal growth temperatures were determined for bulk GaPN layers and for GaPNAs/GaP(N) superlattices, which leads to an increase in the PL intensity and lifetime of the carrier

Van der Waals epitaxial growth of few layers WSe2 on GaP(111)B

2D material epitaxy offers the promise of new 2D/2D and 2D/3D heterostructures with their own specific electronic and optical properties. In this work, we demonstrate the epitaxial growth of few layers WSe2 on GaP(111)B by molecular beam epitaxy. Using a combination of experimental techniques, we emphasize the role of the growth temperature and of a subsequent annealing of the grown layers under a selenium flux on the polytype formed and on its structural and morphological properties. We show that a low growth temperature promotes the formation of the 1T′ and 3R phases depending on the layer thickness whereas a higher growth temperature favours the stable 2H phase. The resulting layers exhibit clear epitaxial relationships with the GaP(111)B substrate with an optimum grain disorientation and mean size of 1.1° and around 30 nm respectively for the 2H phase. Bilayer 2H WSe2/GaP(111)B heterostructures exhibit a staggered type II band alignment and p-doped character of the epi-layer on both p and n-type GaP substrates. This first realisation of stable p-type WSe2 epi-layer on a large-area GaP(111)B substrate paves the way to new 2D/3D heterostructures with great interests in nanoelectronic and optoelectronic applications, especially in the development of new 2D-material p-n junctions.

Design of a High-Gain and Tri-Band Terahertz Microstrip Antenna Using a Polyimide Rectangular Dielectric Column Photonic Band Gap Substrate

A high-gain and tri-band terahertz microstrip antenna with a photonic band gap (PBG) substrate is presented in this paper for terahertz communications. Polyimide dielectric columns are inserted into the silicon substrate to form the PBG substrate to improve the gain of the antenna. The PBG substrate and polyimide substrate constituted a multilayer substrate structure and enabled the multi-band operation of the antenna. The PBG substrate antenna achieves gains of 6.28 dB, 4.84 dB, and 7.66 dB at resonant frequencies of 0.360 THz, 0.580 THz, and 0.692 THz, respectively, outperforming the homogeneous substrate THz microstrip antenna (H antenna) by 1.18 dB, 1.74 dB, and 1.82 dB, respectively. The radiation efficiencies at three operating bands are over 93%, 92%, and 88%, respectively, which are slightly higher than that of the H antenna and greater than that of the standard multi-band antenna.

Survey of Activated Cleaning Chemistries for Low-Stress Post-Chemical Mechanical Planarization Cleaning of Silicon Carbide

Integrated Circuit (IC) technologies have begun transitioning to wide band gap (WBG) substrates (i.e., Silicon carbide (SiC)) due to the intrinsic properties (i.e., high capacitance, thermal stability, and wear resistance) of these semiconducting materials. This has led to the development of Chemical Mechanical Planarization (CMP) processes that use aggressive chemical conditions and increasing mechanical forces to reach optimal material removal rates (MRR). The harsh CMP process parameters often result in contamination/defectivity (i.e., organic residue, abrasive particles, etc.) left on post-polish substrate surfaces and thus posing difficulty within the post-CMP cleaning process. Traditionally, post-CMP cleaning utilizes a polyvinyl alcohol (PVA) brush scrubbing method on the substrate surface. This has been shown to cause secondary defects (i.e., scratches, particle agglomerations, etc.) that inevitably lead to overall device failure. Alternative post-CMP methods utilize non-contact cleaning via megasonic energy to target removing defects (i.e., organic residue, pad debris, particle agglomerations, etc.) and avoid secondary defect generation. This research surveys post-CMP cleaning processes (contact and non-contact) on SiC substrates with various cleaning chemistries (i.e., supramolecular surfactants, catalytic complexes for generating reactive oxygen species (ROS), non-metal catalyst). Initial results show that supramolecular surfactants can produce high particle removal efficiency (PRE) due to their ability to be broken down into their monomeric units and encapsulate any removed residue under both brush and megasonic conditions Additionally, increased ROS generation disrupts the non-covalently adsorbed defects to the SiC surface and leads to an increased cleaning efficiency while decreasing the overall variability of particle removal results. Combining the ROS systems' disruptive power with surfactants' encapsulation mode, a highly efficient clean with low variability can be achieved under low-stress conditions.

Growth of nanotextured thin films of GaInAsP and GaInAsSbBi solid solutions on GaP substrates by pulsed laser deposition

Growth of nanotextured thin films of GaInAsP and GaInAsSbBi solid solutions on GaP substrates by pulsed laser deposition

A simple and efficient process for the synthesis of 2D carbon nitrides and related materials

We describe here a new process for the synthesis of very high quality 2D Covalent Organic Frameworks (COFs), such a C2N and CN carbon nitrides. This process relies on the use of a metallic surface as both a reagent and a support for the coupling of small halogenated building blocks. The conditions of the assembly reaction are chosen so as to leave the inorganic salts by-products on the surface, to further confine the assembly reaction on the surface and increase the quality of the 2D layers. We found that under these conditions, the process directly returns few layers material. The structure/quality of these materials is demonstrated by extensive cross-characterizations at different scales, combining optical microscopy, Scanning Electron Microscopy (SEM)/Transmission Electron Microscopy (TEM) and Energy Dispersive Spectroscopy (EDS). The availability of such very large, high-quality layers of these materials opens interesting perspectives, for example in photochemistry and electronics (intrinsic transport properties, high gap substrate for graphene, etc...).

Modified bow-tie antenna array with efficient electric near-field enhancement for terahertz band

Antenna arrays can induce strong electric near-field enhancement to improve the performance of biological imaging resolution, macromolecule detection sensitivity, and sensing accuracy. However, the use of antenna arrays to regulate both the electric near-field enhancement factor and area has rarely been reported. In this paper, a novel modified bow-tie (MBT) antenna array is proposed for better near-field enhancement performance in terahertz (THz) regime. Using commercially available high frequency structure simulator (HFSS), the dimensions of the MBT antenna array, including gap width, arm length, array period, and substrate thickness, are optimized to improve electric near-field enhancement performance in terms of higher factor, larger area, more controllable peak frequency, and wider 1-dB bandwidth. The as-optimized MBT and bow-tie (BT) THz antenna arrays are fabricated on quartz substrate via lithography and lift-off process. The normalized transmittances of the MBT and BT antenna arrays are characterized by THz time-domain spectroscopy (THz-TDS) and compared with the corresponding simulated near-field enhancement factor and normalized transmittance. The results indicate that the MBT antenna array outperforms the BT antenna array with a three-fold increase in near-field enhancement area and a 66.7% wider 1-dB bandwidth, and therefore can be used to enhance detection sensitivity and sensing accuracy in weak terahertz environment.

Effects of ground plane on a square graphene ribbon patch antenna designed on a high-permittivity substrate with PBG structures

Abstract In this paper, a wide bandwidth (20 GHz) and small sized (200 × 200 × 50 µm3) terahertz (THz) square graphene ribbon antenna using Photonic Band Gap (PBG) substrate are investigated in the 0.6–0.8 THz band. The proposed antenna consists of graphene as radiating patch mounted on four types of ground plane. The important aim of this work is to eliminate the second resonance frequency by utilize a several types of ground plane and keep a single frequency by improving the performance of the proposed antenna. The effect of change ground plane on the performance of antenna is compared, in terms of reflection coefficient, bandwidth, directivity and radiation pattern. The antenna has achieved good gain (7.62 dB) and good directivity (6.38 dB) in comparison to work reported in the literature.

Particle Swarm Optimization Based Design of a Terahertz Antenna with a Modified Photonic Band Gap Substrate for 6G Future Wireless Communications

In this study, an antenna is proposed that operates at THz spectrum for sixth generation (6G) short-range future wireless communications. A modified photonic band gap (MPBG) substrate is employed to design an octagonal ring shaped microstrip patch antenna with wideband and high gain properties. Unlike the conventional photonic band gap (PBG) form, the proposed MPBG substrate structure is created by variable sized cylindrical air holes. The radii of each air cylinder in the row is determined with the help of particle swarm optimization (PSO) algorithm, where the goal is set to achieve the highest gain and impedance bandwidth (S_11≤-10 dB) possible. The simulation results of the antennas that are built on 1) non-PBG, 2) conventional PBG and 3) the proposed MPBG substrate structures are compared. It is observed that the radiation performance is most enhanced by implementing MPBG structure. In comparison to the antenna without PBG, the reported MPBG structure offers almost 300% gain and 11% bandwidth improvement. To summarize, the designed antenna with its proposed MPBG substrate structure achieves an excellent radiation performance within a wide operating bandwidth.

Discrete element analysis for effects of recoating blade and surface morphology of substrate on powder spreading quality

A discrete element method model was established to simulate 316L stainless steel powder spreading process in selective laser melting. The effects of recoating blade speed, assigned gap width and substrate surface morphology on the powder spreading quality was studied. The results showed that lower recoating speed and larger gap width benefited the quality of powder layer. When the angle between the moving direction of recoater and laser scanning direction was greater than 45 °, the density level of the powder layer on the SLM processing surface was higher than that of the flat substrate and more uniform. The quality of the powder layer on the milled surface varied with position obviously, and the maximum density was between the other two types of surfaces, while uniformity of the powder layer was worse than the other two surfaces. This study shows that the quality of powder layer can be controlled by adjusting the setting parameters of the recoater and the surface morphology of the substrate.

Structural Properties and Energy Spectrum of Novel GaSb/AlP Self-Assembled Quantum Dots.

In this work, the formation, structural properties, and energy spectrum of novel self-assembled GaSb/AlP quantum dots (SAQDs) were studied by experimental methods. The growth conditions for the SAQDs' formation by molecular beam epitaxy on both matched GaP and artificial GaP/Si substrates were determined. An almost complete plastic relaxation of the elastic strain in SAQDs was reached. The strain relaxation in the SAQDs on the GaP/Si substrates does not lead to a reduction in the SAQDs luminescence efficiency, while the introduction of dislocations into SAQDs on the GaP substrates induced a strong quenching of SAQDs luminescence. Probably, this difference is caused by the introduction of Lomer 90°-dislocations without uncompensated atomic bonds in GaP/Si-based SAQDs, while threading 60°-dislocations are introduced into GaP-based SAQDs. It was shown that GaP/Si-based SAQDs have an energy spectrum of type II with an indirect bandgap and the ground electronic state belonging to the X-valley of the AlP conduction band. The hole localization energy in these SAQDs was estimated equal to 1.65-1.70 eV. This fact allows us to predict the charge storage time in the SAQDs to be as long as >>10 years, and it makes GaSb/AlP SAQDs promising objects for creating universal memory cells.

Stretchable and Bendable Polydimethylsiloxane- Silver Composite Antenna on PDMS/Air Gap Substrate for 5G Wearable Applications

Stretchable and Bendable Polydimethylsiloxane- Silver Composite Antenna on PDMS/Air Gap Substrate for 5G Wearable Applications

Processes of Current Transport in p-Si-n-(Si<sub>2</sub>)<sub>1−</sub><i><sub>y</sub></i><sub>−</sub><i><sub>z</sub></i>(GaP)<i><sub>y</sub></i>(ZnSe)<i><sub>z</sub></i> Heterostructure Produced by Liquid Phase Epitaxy

The possibility of growing multicomponent epitaxial films of a semiconductor solid solution of molecular substitution (Si2)1−y−z(GaP)y(ZnSe)z on Si and GaP substrates by liquid-phase epitaxy is shown. The distribution profiles of the atoms of the solid solution components Ga, P, Zn, Se, and Si over the thickness of the epitaxial film have been determined. The current-voltage (I−V) characteristics of p-Si-n-(Si2)1−y−z(GaP)y(ZnSe)z heterostructures have been studied. A temperature-independent I−V characteristic has been found, the existence of which is explained on the basis of a theory considering the possibility of "blurring" of the impurity level. By comparing the theoretical and experimental results, the half-width of the blurring band for the energy levels of atoms of Si2 and GaP molecules was determined, which had values equal to 0.146 and 0.34 eV, respectively.

A Conceptual Framework for the Design of Energy-Efficient Vertical Green Façades

This research aims to develop a conceptual framework for a design support model for energy-efficient vertical green façade systems with a focus on their thermal and shading performance. The model applies forecasting and backcasting methods based on an extensive literature review and analysis by the authors, with a particular focus on the energy efficiency parameters of vertical green façades. The key parameters are related to the location (climate, surroundings, orientation of the façade), system type (air gap dimensions, irrigation, structure, and substrate type) and plant characteristics (leaf area index, leaf absorptivity, foliage thickness, stomatal resistance, typical leaf dimensions, leaf emissivity, transmission coefficient, radiation attenuation) determined from actual data collected from buildings. This holistic approach changes the perception of a user and an architect while facilitating the design process. The method’s limitations result from the scarcity of comparative experimental studies. However, the proposed model can be customised for specific conditions, with an increasing number of studies testing energy efficiency parameters comparatively. The article emphasises the vital importance of vertical green façades for built environment decarbonisation and links it to a new conceptual framework to encourage designers to make greater use of vertical green systems that are fully integrated into building energy strategies.

Epitaxial ZnGeP2 Thin Films on Si and GaP by Reactive Combinatorial Sputtering in Phosphine

Modern optoelectronic devices are constrained to a fixed collection of band gap and lattice parameter combinations by the limited number of semiconductors that can be epitaxially integrated with high crystal quality. II–IV–V2 compounds are promising materials to break this paradigm as changes to the cation lattice site disorder can modify the band gap without a substantial change to the lattice parameter. ZnGeP2 is a particularly interesting member of this group as it is lattice-matched to Si and GaP, but substantial work is needed to understand and improve the epitaxial growth of ZnGeP2. In this paper, we report on the growth of epitaxial ZnGeP2 on Si and GaP substrates via reactive combinatorial sputtering in phosphine gas. Reciprocal space maps revealed that films on both GaP and Si have high crystalline quality, matching that of the substrate. The out-of-plane lattice parameter was found to increase with increasing Ge content, displaying an alloy-like behavior. Films deposited on Si displayed a much larger range for the (004) peak full width at half maximum (FWHM) than those deposited on GaP. Due to the growth of a lower-symmetry material, ZnGeP2, on a higher-symmetry substrate, Si, it is likely that the films grown on Si have antiphase domains and larger threading dislocation densities than those on GaP. Electron channeling contrast imaging revealed the films on GaP to be largely dislocation-free. In the films deposited on Si, the optical absorption onset energies trended toward lower energies with larger (004) FWHM values. These results suggest that the defects in the films on Si that result in a broadened (004) FWHM cause sub-band gap absorption. This work provides the first combinatorial study of epitaxial ZnGeP2 on Si and GaP and demonstrates the strong potential for the growth of high-quality epitaxial ZnGeP2 with future work optimizing synthesis conditions and substrate preparation.

Manganese phosphide nanoclusters embedded in epitaxial gallium phosphide grown from the vapor phase: Non-negligible role of Mn diffusion in growth kinetics

Orthorhombic MnP nanoclusters are formed in GaP epitaxial films grown by metalorganic vapor phase epitaxy on GaP(001) substrates, which are labeled as GaP:MnP/GaP(001). Polycrystalline MnP films have also been grown from the vapor phase on GaP substrates and are labeled as (p-c)MnP/GaP(001). Both GaP:MnP/GaP(001) epilayers and (p-c)MnP/GaP (001) films show a very rich texture, which has been previously characterized by three dimensional x-ray diffraction reciprocal space maps combined with transmission electron microscopy measurements. Heterostructures (HSs) containing multiple layers of (p-c)MnP/GaP and of GaP:MnP/GaP have been designed and grown with the same process. These HSs add new elements to our understanding of the growth mechanisms involved in these complex systems. In particular, it is shown that Mn diffusion during growth is strongly enhanced leading to a picture of MnP cluster coalescence, which explains some of their properties, such as the variation of their spatial distribution within the GaP matrix with the epilayer thickness. We report an Mn atomic diffusion coefficient of (1.5 ± 0.2) × 10−15 cm2/s in these films at 650 °C. The data are compatible with the superdiffusion of Mn, where the square of the diffusion length as a function of time (t) obeys λD2∝t1+α with an estimated value of α≈0.52.

Enhanced Optical Biosensing by Aerotaxy Ga(As)P Nanowire Platforms Suitable for Scalable Production.

Sensitive detection of low-abundance biomolecules is central for diagnostic applications. Semiconductor nanowires can be designed to enhance the fluorescence signal from surface-bound molecules, prospectively improving the limit of optical detection. However, to achieve the desired control of physical dimensions and material properties, one currently uses relatively expensive substrates and slow epitaxy techniques. An alternative approach is aerotaxy, a high-throughput and substrate-free production technique for high-quality semiconductor nanowires. Here, we compare the optical sensing performance of custom-grown aerotaxy-produced Ga(As)P nanowires vertically aligned on a polymer substrate to GaP nanowires batch-produced by epitaxy on GaP substrates. We find that signal enhancement by individual aerotaxy nanowires is comparable to that from epitaxy nanowires and present evidence of single-molecule detection. Platforms based on both types of nanowires show substantially higher normalized-to-blank signal intensity than planar glass surfaces, with the epitaxy platforms performing somewhat better, owing to a higher density of nanowires. With further optimization, aerotaxy nanowires thus offer a pathway to scalable, low-cost production of highly sensitive nanowire-based platforms for optical biosensing applications.

Investigation of a nanostructured GaP/MoS2 p-n heterojunction photodiode

We report on the properties of a GaP/MoS2 heterojunction prepared on a nanocone (NC)-structured GaP substrate and a planar GaP substrate. The nanocone-structured GaP substrate was prepared by the growth of GaP NCs at gold seeds on a ⟨111⟩B GaP substrate at 650 °C by metal organic vapor phase epitaxy. At this growth temperature, most NCs exhibited a hexagonal symmetry with six heavily facetted sides that contained numerous facets, ledges, and edges with a large surface area. A thin Mo layer was deposited on both types of GaP substrates by direct current magnetron sputtering. The Mo layer was then sulfurated at 700 °C and turned into a MoS2 layer. Electrical and optical characterization gave evidence that a PN heterojunction formed between GaP and MoS2 during the sulfuration process. The spectral response measurement showed two separate regions between 400 and 550 nm linked with the generation of carriers in GaP and between 550 and 1100 nm associated with the generation of carriers in the MoS2 layer. The planar GaP/MoS2 heterojunction generated a lower photocurrent compared with the GaP/MoS2 heterojunction that formed on the nanocone-structured GaP substrate. The results support theoretical assumptions that edge rich substrates can help to increase the quality of deposited 2D materials.

Selective-Area Epitaxy of InGaAsP Buffer Multilayer for In-Plane InAs Nanowire Integration.

In order to use III–V compound semiconductors as active channel materials in advanced electronic and quantum devices, it is important to achieve a good epitaxial growth on silicon substrates. As a first step toward this, we report on the selective-area growth of GaP/InGaP/InP/InAsP buffer layer nanotemplates on GaP substrates which are closely lattice-matched to silicon, suitable for the integration of in-plane InAs nanowires. Scanning electron microscopy reveals a perfect surface selectivity and uniform layer growth inside 150 and 200 nm large SiO2 mask openings. Compositional and structural characterization of the optimized structure performed by transmission electron microscopy shows the evolution of the major facet planes and allows a strain distribution analysis. Chemically uniform layers with well-defined heterointerfaces are obtained, and the topmost InAs layer is free from any dislocation. Our study demonstrates that a growth sequence of thin layers with progressively increasing lattice parameters is effective to efficiently relax the strain and eventually obtain high quality in-plane InAs nanowires on large lattice-mismatched substrates.