All-Optic Logical Operations Based on the Visible-Near Infrared Bipolar Optical Response.

The burgeoning need for extensive data processing has sparked enthusiasm for the development of a novel optical logic gate platform. In this study, junction field-effect phototransistors based on molybdenum disulfide/Germanium (MoS/Ge) heterojunctions are constructed as optical logic units. This device demonstrates a positive photoresponse that is attributed to the photoconductivity effect occurring upon irradiation with visible (Vis) light.

Near-infrared detection based on the excitation of hot electrons in Au/Si microcone array.

Although the photoresponse cut-off wavelength of Si is about 1100 nm due to the Si bandgap energy, the internal photoemission effect (IPE) of the Au/Si junction in Schottky detector can extend the absorption wavelength, which makes it a promising candidate for the Si-based infrared detector. However, due to low light absorption, low photon-electron interaction, and poor electron injection efficiency, the near-infrared light detection efficiency of the Schottky detector is still insufficient. The synergistic effect of Si nano/microstructures with a strong light trapping effect and nanoscale Au films with surface plasmon enhanced absorption may provide an effective solution for improving the detection efficiency.

Hexagonal-Ge Nanostructures with Direct-Bandgap Emissions in a Si-Based Light-Emitting Metasurface.

Si-based emitters have been of great interest as an ideal light source for monolithic optical-electronic integrated circuits (MOEICs) on Si substrates. However, the general Si-based material is a diamond structure of cubic lattice with an indirect band gap, which cannot emit light efficiently. Here, hexagonal-Ge (H-Ge) nanostructures within a light-emitting metasurface consisting of a cubic-SiGe nanodisk array are reported.

Unique Enhancement of the Whispering Gallery Mode in Hexagonal Microdisk Resonator Array with Embedded Ge Quantum Dots on Si.

The coupling between the quantum dots (QDs) and silicon-based microdisk resonator facilitates enhancing the light-matter interaction for the novel silicon-based light source. However, the typical circular microdisks embedded with Ge QDs still have several issues, such as wide spectral bandwidth, difficult mode selection, and low waveguide coupling efficiency. Here, by a promising structural modification based on the mature nanosphere lithography (NSL), we fabricate a large area hexagonal microdisk array embedded with Ge QDs in order to enhance the near-infrared light emissions by a desired whispering gallery modes (WGMs).

Competitive Growth of Ge Quantum Dots on a Si Micropillar with Pits for a Precisely Site-Controlled QDs/Microdisk System.

Semiconductor quantum dots (QDs)/microdisks promise a unique system for comprehensive studies on cavity quantum electrodynamics and great potential for on-chip integrated light sources. Here, we report on a strategy for precisely site-controlled Ge QDs in SiGe microdisks via self-assembly growth of QDs on a micropillar with deterministic pits and subsequent etching. The competitive growth of QDs in pits and at the periphery of the micropillar is disclosed.

Diverse field-effect characteristics and negative differential transconductance in a graphene/WS/Au phototransistor with a Ge back gate.

We propose an infrared-sensitive negative differential transconductance (NDT) phototransistor based on a graphene/WS/Au double junction with a SiO/Ge gate. By changing the drain bias, diverse field-effect characteristics can be achieved. Typical p-type and n-type behavior is obtained under negative and positive drain bias, respectively.

Self-Powered Bidirectional Photoresponse in High-Detectivity WSe Phototransistor with Asymmetrical van der Waals Stacking for Retinal Neurons Emulation.

An artificial retina system shows a promising potential to achieve fast response, low power consumption, and high integration density for vision sensing systems. Optoelectronic sensors, which can emulate the neurobiological functionalities of retinal neurons, are crucial in the artificial retina systems. Here, we propose a WSe phototransistor with asymmetrical van der Waals (vdWs) stacking that can be used as an optoelectronic sensor in artificial retina systems.

Extensive Broadband Near-Infrared Emissions from GeSi Alloys on Micro-Hole Patterned Si(001) Substrates.

Broadband near-infrared (NIR) luminescent materials have been continuously pursued as promising candidates for optoelectronic devices crucial for wide applications in night vision, environment monitoring, biological imaging, etc. Here, graded GeSi (x = 0.1-0.

Artificial Graphene on Si Substrates: Fabrication and Transport Characteristics.

Artificial graphene (AG) based on a honeycomb lattice of semiconductor quantum dots (QDs) has been of great interest for exploration and applications of massless Dirac Fermions in semiconductors thanks to the tunable interplay between the carrier interactions and the honeycomb topology. Here, an innovative strategy to realize AG on Si substrates is developed by fabricating a honeycomb lattice of Au nanodisks on a Si/GeSi quantum well. The lateral potential modulation induced by the nanoscale Au/Si Schottky junction results in the formation of quantum dots arranged in a honeycomb lattice to form AG.

Infrared broadband enhancement of responsivity in Ge photodetectors decorated with Au nanoparticles.

A broadband, high-performance infrared Ge photodetector decorated with Au nanoparticles (NPs) is proposed. Photoelectronic characterization demonstrated that the responsivity of devices decorated with Au NPs is as high as 3.95 A/W at a wavelength of 1550 nm.

Photoelectrical Properties Investigated on Individual Si Nanowires and Their Size Dependence.

Periodically ordered arrays of vertically aligned Si nanowires (Si NWs) are successfully fabricated with controllable diameters and lengths. Their photoconductive properties are investigated by photoconductive atomic force microscopy (PCAFM) on individual nanowires. The results show that the photocurrent of Si NWs increases significantly with the laser intensity, indicating that Si NWs have good photoconductance and photoresponse capability.

Nanoscale growth of a Sn-guided SiGeSn alloy on Si (111) substrates by molecular beam epitaxy.

Here, SiGeSn nanostructures were grown molecular beam epitaxy on a Si (111) substrate with the assistance of Sn droplets. Owing to the thermal effect and the compressive strain induced by a lattice mismatch, Si and Sn atoms were successfully incorporated into the Ge matrix during the Sn-guided Ge deposition process. A low growth temperature of 350 °C produced a variety of SiGeSn nanostructures of different sizes, attributed to the variation of the initial Sn droplet size.

Promising modulation of self-assembled Ge-rich QDs by ultra-heavy phosphorus doping.

Self-assembled Ge-rich quantum dots (QDs) can not only act as a prototype model for the fundamental studies of heteroepitaxial growth but also have great potential in optoelectronic devices for telecommunication and monolithic optical-electronic integrated circuits. Here, we report the unique features of Ge-rich QDs ultra-heavily doped with phosphorus (P) and embedded in a thin SiGe alloy film on Si (001) substrates. The ultra-heavy P doping considerably reduces the size of Ge-rich QDs and improves their uniformity.

Manipulations of light by ordered micro-holes in silicon substrates.

Ordered micro-holes with controllable period, diameter and depth are fabricated in Si (001) substrates via a feasible approach based on nanosphere lithography. They dramatically reduce the reflectance in a broad wavelength range of 400-1000 nm, which can be deliberately modulated by tailoring their geometrical parameters. The simulated reflectance via finite-difference time-domain (FDTD) method agrees well with the experimental data.

GeSi virtual-layer enhanced ferromagnetism in self-assembled MnGe quantum dots grown on Si wafers by molecular beam epitaxy.

Self-assembled MnGe quantum dots (QDs) on a Si substrate or GeSi virtual substrate (VS) were grown by molecular beam epitaxy. The GeSi VS of different thicknesses and Ge compositions x were utilized to modulate the ferromagnetic properties of the above QDs. The MnGe QDs on GeSi VS show a significantly enhanced ferromagnetism with a Curie temperature above 220 K.

Fabrication of High-Quality and Strain-Relaxed GeSn Microdisks by Integrating Selective Epitaxial Growth and Selective Wet Etching Methods.

GeSn is a promising material for the fabrication of on-chip photonic and nanoelectronic devices. Processing techniques dedicated to GeSn have thus been developed, including epitaxy, annealing, ion implantation, and etching. In this work, suspended, strain-relaxed, and high-quality GeSn microdisks are realized by a new approach without any etching to GeSn alloy.

An array of SiGe nanodisks with Ge quantum dots on bulk Si substrates demonstrating a unique light-matter interaction associated with dual coupling.

Si-Based microdisks with Ge quantum dots (QDs) have been of great interest due to their potential as the desired light source for monolithic optical-electronic integrated circuits (MOEICs), as well as in the studies of cavity quantum electrodynamics (CQED). Here, we report on unique SiGe nanodisk arrays with embedded Ge QDs directly realized on bulk Si substrates. Their superior optoelectronic properties are demonstrated by remarkably enhanced photoluminescence due to the coupling between QD emissions and cavity modes of the nanodisk, even though the size of the nanodisk is much smaller than the wavelengths of cavity modes.

The photoelectric response of the graphene/GeSi QDs hybrid structure.

In this work, the photoelectric response properties of the graphene/GeSi QDs hybrid structure were demonstrated by measuring the I-V curve, and the incident photon-to-current conversion efficiency (IPCE). The maximal on-off ratio of the current value reaches 1500 at 10 K, due to the competition between the carrier freeze-out effect and the recombination center effect. The IPCE of the hybrid structure under different incident light indicated that the photoelectric response of hybrid structure is most sensitive to the ultraviolet light (325 nm), which is attributed to the enhanced ultraviolet absorption of graphene surface plasmon in the hybrid structure.

Toward precise site-controlling of self-assembled Ge quantum dots on Si microdisks.

A feasible route is developed toward precise site-controlling of quantum dots (QDs) at the microdisk periphery, where most microdisk cavity modes are located. The preferential growth of self-assembled Ge QDs at the periphery of Si microdisks is discovered. Moreover, both the height and linear density of Ge QDs can be controlled by tuning the amount of deposited Ge and the microdisk size.

Electrostatic effect of Au nanoparticles on near-infrared photoluminescence from Si/SiGe due to nanoscale metal/semiconductor contact.

Photoluminescence (PL) from Si and SiGe is comprehensively modified by Au NPs under excitation without surface plasmon resonance. Moreover, the PL sensitively depends on the size of the Au NPs, the excitation power and the thickness of the Si layer between the Au NPs and SiGe. A model is proposed in terms of the electrostatic effects of Au NPs naturally charged by electron transfer through the nanoscale metal/semiconductor Schottky junction without an external bias or external injection of carriers.

Promising features of low-temperature grown Ge nanostructures on Si(001) substrates.

High-quality Ge nanostructures are obtained by molecular beam epitaxy of Ge on Si(001) substrates at 200 °C and ex situ annealing at 400 °C. Their structural properties are comprehensively characterized by atomic force microscopy, transmission electron microscopy and Raman spectroscopy. It is disclosed that they are almost defect free except for some defects at the Ge/Si interface and in the subsequent Si capping layer.

Large-Area Au-Nanoparticle-Functionalized Si Nanorod Arrays for Spatially Uniform Surface-Enhanced Raman Spectroscopy.

In this study, large-area hexagonal-packed Si nanorod (SiNR) arrays in conjunction with Au nanoparticles (AuNPs) were fabricated for surface-enhanced Raman spectroscopy (SERS). We have achieved ultrasensitive molecular detection with high reproducibility and spatial uniformity. A finite-difference time-domain simulation suggests that a wide range of three-dimensional electric fields are generated along the surfaces of the SiNR array.