Novel Applications In Optoelectronics Research Articles

Unveiling Polymorphs and Polytypes of the 2D Layered Semiconducting Gallium Monosulfide

AbstractPolymorphism is gaining attention among van der Waals layered materials. In the case of gallium monosulfide, a hexagonal phase has predominantly been reported. Here the successful growth of rhombohedral gallium sulfide (GaS) with space group on sapphire substrates using chemical vapor deposition (CVD) is presented. Crystallographic analysis reveals that the CVD GaS has preferred 𝑐‐axis orientation, low microstrain and moderate mosaicity. A combined approach of X‐ray diffraction, Raman spectroscopy and photoluminescence measurements with first principles calculations is used to determine phononic and photonic properties of the rhombohedral GaS with direct band gap of 2.55 eV and near‐blue light emission at room temperature. These results pave the way to novel applications in optoelectronics and photonics, particularly for development of efficient light‐emitting devices such as LEDs or lasers, quantum dots, photodetectors, and integrated photonic circuits.

Dynamics of Two Distinct Exciton Populations in Methyl-Functionalized Germanane.

Methyl-substituted germanane is an emerging material that has been proposed for novel applications in optoelectronics, photoelectrocatalysis, and biosensors. It is a two-dimensional semiconductor with a strong above-gap fluorescence associated with water intercalation. Here, we use time-resolved photoluminescence spectroscopy to understand the mechanism causing this fluorescence. We show that it originates from two distinct exciton populations. Both populations recombine exponentially, accompanied by the thermally activated transfer of exciton population from the shorter- to the longer-lived type. The two exciton populations involve different electronic levels and couple to different phonons. The longer-lived type of exciton migrates within the disordered energy landscape of localized recombination centers. These outcomes shed light on the fundamental optical and electronic properties of functionalized germanane, enabling the groundwork for future applications in optoelectronics, light harvesting, and sensing.

Paraffin-Enabled Compressive Folding of Two-Dimensional Materials with Controllable Broadening of the Electronic Band Gap.

The capability to manipulate the size of the electronic band gap is of importance to semiconductor technology. Among these, a wide direct band gap is particularly helpful in optoelectronic devices due to the efficient utilization of blue and ultraviolet light. Here, we reported a paraffin-enabled compressive folding (PCF) strategy to widen the band gap of two-dimensional (2D) materials. Due to the large thermal expansion coefficient of paraffin, folded 2D materials can be achieved via thermal engineering of the paraffin-assisted transfer process. It can controllably introduce 0.2-1.3% compressive strain onto folded structures depending on the temperature differences and transfer the folding product to both rigid and soft substrates. Exemplified by MoS2, its folded multilayers demonstrated blue-shifts at direct gap transition peaks, six times stronger photoluminescence intensity, almost double mobility, and 20 times higher photoresponsivity over unfolded MoS2. This PCF strategy can attain controllable widening band gap of 2D materials, which will open up novel applications in optoelectronics.

Atomically Thin Hexagonal Boron Nitride and Its Heterostructures.

Atomically thin hexagonal boron nitride (h-BN) is an emerging star of 2D materials. It is taken as an optimal substrate for other 2D-material-based devices owing to its atomical flatness, absence of dangling bonds, and excellent stability. Specifically, h-BN is found to be a natural hyperbolic material in the mid-infrared range, as well as a piezoelectric material. All the unique properties are beneficial for novel applications in optoelectronics and electronics. Currently, most of these applications are merely based on exfoliated h-BN flakes at their proof-of-concept stages. Chemical vapor deposition (CVD) is considered as the most promising approach for producing large-scale, high-quality, atomically thin h-BN films and heterostructures. Herein, CVD synthesis of atomically thin h-BN is the focus. Also, the growth kinetics are systematically investigated to point out general strategies for controllable and scalable preparation of single-crystal h-BN film. Meanwhile, epitaxial growth of 2D materials onto h-BN and at its edge to construct heterostructures is summarized, emphasizing that the specific orientation of constituent parts in heterostructures can introduce novel properties. Finally, recent applications of atomically thin h-BN and its heterostructures in optoelectronics and electronics are summarized.

STRUCTURAL, OPTICAL AND MORPHOLOGICAL INVESTIGATIONS OF Fe-DOPED SnS THIN FILMS

SnS could have novel applications in optoelectronics including solar cell devices, sensors, batteries and also in biomedical sciences. Fe-doped SnS thin films were prepared on glass substrates using chemical spray pyrolysis (CSP) method. Pure and Fe-doped SnS thin films were deposited onto microscopic glass substrates using the spray pyrolysis technique. The precursors of SnCl2·2H2O (0.1 M) and thiourea (0.1 M) were dissolved separately in a solution containing deionised water and isopropyl alcohol in proper ratio. Equal volumes of these two solutions were mixed together and sprayed onto the microscopic glass substrates at a substrate temperature of 450⁰C. Fe was doped with SnS thin films using FeCl3 (5 at.%, 7 at.%, 9 at.%, and 11 at.%) as the dopant source. Structural, optical, vibrational, structural, morphological properties were studied.

Thermal conductivity of hexagonal Si, Ge, and Si1-xGex alloys from first-principles

Hexagonal Si and Ge with a lonsdaleite crystal structure are allotropes of silicon and germanium that have recently been synthesized. These materials as well as their alloys are promising candidates for novel applications in optoelectronics. In this paper, we systematically study the phonon transport and thermal conductivity of hexagonal Si, Ge, and their alloys by using the first-principle-based Peierls-Boltzmann transport equation approach. Both three-phonon and four-phonon scatterings are taken into account in the calculations as the phonon scattering mechanisms. The thermal conductivity anisotropy of these materials is identified. While the thermal conductivity parallel to the hexagonal plane for hexagonal Si and Ge is found to be larger than that perpendicular to the hexagonal plane, alloying effectively tunes the thermal conductivity anisotropy by suppressing the thermal conductivity contributions from the middle-frequency phonons. The importance of four-phonon scatterings is assessed by comparing the results with the calculations without including four-phonon scatterings. We find that four-phonon scatterings cannot be ignored in hexagonal Si and Ge as the thermal conductivity would be overestimated by around 10% (40%) at 300 K (900) K. In addition, the phonon mean free path distribution of hexagonal Si, Ge, and their alloys is also discussed.

Interplay of hot electrons from localized and propagating plasmons

Plasmon-induced hot-electron generation has recently received considerable interest and has been studied to develop novel applications in optoelectronics, photovoltaics and green chemistry. Such hot electrons are typically generated from either localized plasmons in metal nanoparticles or propagating plasmons in patterned metal nanostructures. Here we simultaneously generate these heterogeneous plasmon-induced hot electrons and exploit their cooperative interplay in a single metal-semiconductor device to demonstrate, as an example, wavelength-controlled polarity-switchable photoconductivity. Specifically, the dual-plasmon device produces a net photocurrent whose polarity is determined by the balance in population and directionality between the hot electrons from localized and propagating plasmons. The current responsivity and polarity-switching wavelength of the device can be varied over the entire visible spectrum by tailoring the hot-electron interplay in various ways. This phenomenon may provide flexibility to manipulate the electrical output from light-matter interaction and offer opportunities for biosensors, long-distance communications, and photoconversion applications.

Property of Zinc Oxide (Zno) Nanostructures Potential for Biomedical System and Its Common Growth Mechanism

Zinc Oxide (ZnO) nanomaterials have received broad attention thanks to their distinguished performance in electronics, optics and photonics. Due to the novel applications in optoelectronics, sensors, transducers and biomedical sciences, ZnO materials have become a leading edge in nanotechnology. Therefore, the properties of ZnO nanostructures potential for applying in biotechnology are marked along with the relevant common growth mechanism aim to provide the vital information about the growing field related to nano-ZnO in the biomedical system with environmental friendly nature and biocompatibility

Functional nanogenerators as vibration sensors enhanced by piezotronic effects

ZnO nanomaterials have been shown to have novel applications in optoelectronics, energy harvesting and piezotronics, due to their coupled semiconducting and piezoelectric properties. Here a functional nanogenerator (FNG) based on ZnO nanowire arrays has been fabricated, which can be employed to detect vibration in both self-powered (SP) and external-powered (EP) modes. In SP mode, the vibration responses of the FNG can be measured through converting mechanical energy directly into an electrical signal. The FNG shows consistent alternating current responses (relative error < 0.37%) at regular frequencies from 1 to 15 Hz. In EP mode, the current responses of FNG are significantly enhanced via the piezotronic effect. Under a forward bias of 3 V, the sensor presented a sensitivity of 3700% and an accurate measurement (relative error < 0.91%) of vibration frequencies in the range 0.05–15 Hz. The results show that this type of functional nanogenerator sensor can detect vibration in both SP and EP modes according to the demands of the applications.

Self-assembled nanoarchitectures of polar nanobelts/nanowires

This article reviews the most recent progress in the synthesis of polar-surface dominated semiconducting and piezoelectric ZnO nanostructures: including nanosprings, nanohelices, nanorings, nanobows and nanodisks. These structures were formed by self-assembly of polar nanobelts/nanowires as driven by minimizing electrostatic energy owing to spontaneous polarization. The nanostructures could have novel applications in optoelectronics, sensors, transducers and resonators.

Nanostructures of zinc oxide

Zinc oxide (ZnO) is a unique material that exhibits semiconducting, piezoelectric, and pyroelectric multiple properties. Using a solid-vapor phase thermal sublimation technique, nanocombs, nanorings, nanohelixes/nanosprings, nanobows, nanobelts, nanowires, and nanocages of ZnO have been synthesized under specific growth conditions. These unique nanostructures unambiguously demonstrate that ZnO is probably the richest family of nanostructures among all materials, both in structures and properties. The nanostructures could have novel applications in optoelectronics, sensors, transducers, and biomedical science because it is bio-safe.

Electronic properties of AlGaAs-based biperiodic superlattices via pseudopotential calculations

According to recent model studies, AlGaAs-based biperiodic superlattices (SLs), in which every second GaAs slab (`quantum-well' layer) and/or every second AlAs slab (`quantum-barrier' layer) is of a different width, exhibit superior characteristics as compared to usual SLs with simple two-layer well/barrier period. Consequently, they are found promising for novel applications in optoelectronics. However, the transferability of conclusions based on results of simplified approaches to real systems is often questionable. Therefore, we have carried out more reliable pseudopotential computations of the electronic level structure and space-charge distributions for [100]-oriented biperiodic (GaAs)k(AlAs)l(GaAs)m(AlAs)n SLs with variable layer thicknesses. More specifically, we have employed a standard supercell calculation scheme with a plane wave basis set and implemented modern empirical pseudopotentials. The SL potential resulting from the two different GaAs and/or AlAs slabs within the SL period yields miniband splittings and specific spatial redistributions of states. While our results obtained for the GaAs Γ-valley-derived minibands reproduce the characteristics predicted by simple-model approaches, the corresponding features of the AlAs X-valley-derived minibands, which are neglected in most model studies although being of a particular importance for thin-layer systems, are discussed for biperiodic SLs for the first time.

The effects of laser irradiation on InGaAs/GaAs multiple quantum wells grown by metalorganic molecular beam epitaxy

We studied the effects of Ar ion laser irradiation during the growth of InGaAs/ GaAs multiple quantum wells (MQW) structures by metalorganic molecular beam epitaxy. Structural and optical properties were characterized by Nomarski microscopy, Dektak stylus profiler, and low-temperature photoluminescence (PL) measurements. For MQW structures grown at a relatively low substrate temperature (500°C), the laser irradiation influences greatly the growth process of the In^Ga^^As well and results in a large blue shift of about 2000A in the PL peak. Such a large blue shift suggests that laser modification during growth could have some novel applications in optoelectronics. On the other hand, the laser irradiation has relatively small effects on samples grown at a higher substrate temperature (550°C).

Porous silicon pore filling by metal electroplating

Porous silicon can be used as an insulating material in Si devices and as a membrane for ion or molecule separation. Its recently demonstrated photo- and electro-luminescence properties may find novel applications in optoelectronics. Porous silicon has a large internal surface, and, with its pores filled with conducting materials, can form a capacitor with a high charge storage capacity. Recently, thin metal films have been electroplated on porous silicon substrates. These films were then detached and used as condenser microphone diaphragms. Electroplated metal films can also provide electrical contacts to an electro-luminescent porous silicon structure. In this paper, we report our TEM study of a copper electroplating process. We found that in such a process copper preferentially deposits from the bottom of the pore tips upward and fills the entire length of each pore as well as the horizontal side branches.Anodization of silicon was performed in an aqueous HF solution to form a porous layer. Silicon substrates used in this experiment were n-type, (l00)-oriented wafers with a doping concentration of 1017 cm−3 and p-type, (l00)-oriented wafers with a doping concentration of 1019 cm-3.