Ge QDs Research Articles

Self-power, multiwavelength photodetector based on a Sn-doped Ge quantum dots/hexagonal silicon nanowire heterostructure.

Tin-doped germanium quantum dots (Sn-doped Ge QDs)-decorated hexagonal silicon nanowires (h-Si NWs) were adopted to overcome the low infrared response of silicon and the excess dark current of germanium. High-quality Sn-doped Ge QDs with a narrow bandgap can be achieved through Ge-Sn co-sputtering on silicon nanowires by reducing the contact area between heterojunction materials and Sn-induced germanium crystallization. The absorption limit of the heterostructure is extended to 2.2 µm, and it is sensitive to 375-1550 nm light at 0 V, which has optimality at 1342 nm, with a photo-to-dark current ratio of over 815, a responsivity of 0.154 A/W, and a response time of 0.93 ms. The superior performance of the Sn-doped Ge QDs/h-Si NW photodetector in multiwavelength is attractive for multi-scenario applications.

A Stranski–Krastanov to Volmer–Weber transition in the growth mode of self-assembled quantum dots

We present recent experiments for tensile-strained Ge QDs on InAlAs(111)A where we observe that growth proceeds via the Stranski–Krastanov (SK) growth mode at lower temperatures and transitions to the Volmer–Weber (VW) growth mode at higher temperatures. We discuss atomistic kinetic Monte Carlo simulations that show how the SK to VW growth mode transition is affected by model parameters. We find that systems are more likely to transition from a SK to a VW mode when the bond energy between substrate atoms is weaker than the bond energy between atoms of the deposited material. We also show how entropic effects due to intermixing can stabilize a layer-by-layer growth mode in certain parameter regimes.

Electrical and dielectric characterization of Ge quantum dots embedded in MIS structure (AuPd/SiO2:Ge QDs/n-Si) grown by MBE

Monocrystalline Germanium quantum dots (Ge QDs), grown by molecular beam epitaxy (MBE), are intricately embedded within a SiO2 oxide layer of a metal-insulator-semiconductor (MIS) structure, catering to optoelectronic applications. These monocrystalline Ge QDs exhibit high density (D ∼ 5 x 1012 cm−2), possess a spherical morphology, and an average size of 6 nm with narrow size distribution. A comprehensive investigation into the influence of these quantum dots on the electrical transport and dielectric properties of the metal-insulator-semiconductor (MIS) structure was conducted through current-voltage (I–V) spectroscopy and impedance spectroscopy. Notably, I–V measurements demonstrate that Ge QDs enhance conduction phenomena, thereby improving electrical transport within the MIS structure. Furthermore, the capacitance-voltage (C–V) and conductance-voltage (G-V) measurements, spanning the inversion and accumulation regions, demonstrate a memory effect induced by Ge QDs within the MOS structure. Extensive analysis of dielectric parameters, including permittivity (ε′), dielectric loss (ε”), dissipation factor (tanδ), as well as electrical modulus (M’ and M”), across a broad frequency range and under varying bias voltages, reveals no anomalous electrical or dielectric behavior attributable to the presence of Ge QDs in MIS structure. Consequently, these findings affirm the viability of the novel MIS structures with Ge QDs for the development of optoelectronic devices such as photodetectors or solar cells.

Ge QDs in α-GeOx nano-films grown by two stage process based on Rf-magnetron sputtering

Ge QDs in α-GeOx nano-films grown by two stage process based on Rf-magnetron sputtering

Fabrication and Characterization of nMOS Inverters Utilizing Quantum Dot Gate Field Effect Transistor (QDGFET) for SRAM Device

This paper presents experimental results of nMOS quantum dot gate field effect transistor (QDGFET) based inverter devices for SRAM devices. A three-state inverter device was fabricated and tested with Si/SiO2 quantum dots. The work performed here builds off previous works performed with Si/SiO2 dot-based inverters which used two layers of quantum dots. This research explores multi-state SRAM device operation. A three-state (Si QDs) and a four-state (Si and Ge QDs) inverter are described, and they will allow for multistate logic devices to be utilized in everyday logic chips, which will require less devices to perform the same tasks as conventional devices, double the capacity of the device, and require less power, which will generate less of a thermal footprint. The data of the Half Cell SRAM, comprised of one access transistor and an inverter along with a capacitor, is presented here.

Ultraviolet-Visible-Near Infrared Broadband Photodetector Based on Electronspun Disorder ZnO Nanowires/Ge Quantum Dots Hybrid Structure

Ultraviolet-visible-near infrared broadband photodetectors have significant prospects in many fields such as image sensing, communication, chemical sensing, and day and nighttime surveillance. Hybrid one-dimensional (1D) and zero-dimensional (0D) materials are attractive for broadband-responsive photodetectors since its unique charges transfer characteristics and facile fabrication processes. Herein, a Si/ZnO nanowires/Ge quantum dots photodetector has been constructed via processes that combined electrospinning and spin-coating methods. A broadband response behavior from ultraviolet to near-infrared (from 250 to 1550 nm) is observed. The responsivity of the hybrid structure increases around three times from 550 to 1100 nm compared with the pure Si photodetector. Moreover, when the photodetector is illuminated by a light source exceeding 1100 nm, such as 1310 and 1550 nm, there is also a significant photoresponse. Additionally, the ZnO NWs/Ge quantum dots heterostructure is expected to be used in flexible substrates, which benefits from electrospinning and spin-coating processes. The strategy that combines 1D ZnO NWs and 0D solution-processed Ge QDs nanostructures may open a new avenue for flexible and broadband photodetector.

Growth and characterization of Ge QDs embedded in an α-GeOx (x < 0.1) matrix produced by magnetron sputtering and a post-grown annealing stage at low temperatures

Growth and characterization of Ge QDs embedded in an α-GeOx (x < 0.1) matrix produced by magnetron sputtering and a post-grown annealing stage at low temperatures

Highly Tensile-Strained Self-Assembled Ge Quantum Dots on InP Substrates for Integrated Light Sources

Highly tensile-strained Ge quantum dots (TS-Ge-QDs) emitting structures with different size were successfully grown on InP substrates by molecular beam epitaxy. Dislocation-free TS-Ge-QDs were observed by transmission electron microscopy. Finite element modeling indicates a maximum tensile strain of 4.5% in the Ge QDs, which is much larger than the required strain to achieve direct band gap conversion of Ge based on theoretical prediction. Photoluminescence (PL) from a direct band-gap-like transition of TS-Ge-QDs with a peak energy of 0.796 eV was achieved and confirmed by the etch depth-dependent PL, temperature-dependent PL, and excitation-power-dependent PL. In addition, a strong defect-related peak of 1 eV was observed at room temperature. The band structure of the TS-Ge-QDs emitting structures was calculated to support the experimental results of PL spectra. Achieving PL from direct band-gap-like transitions of TS-Ge-QDs provides encouraging evidence of this promising highly tensile strained semiconductor-nanostructure-based platform for future photonics applications such as integrated light sources.

Highly-dispersed Ge quantum dots in carbon frameworks for ultra-long-life sodium ion batteries

The high dispersion of Ge QDs in carbon frameworks could effectively avoid the agglomeration of Ge particles. As the anode material for sodium ion batteries, the Ge@C nanocomposite shows ultra-long cycle life and high rate capability.

Navigating 2D Monoelemental Materials (Xenes) for Cancer Nanomedicine

Contributing to this issue of Matter, Wei Tao, Tian Xie, and colleagues now demonstrate the killing of two birds (inhibition of tumor recurrence and wound infection) with one stone (germanene-based surgical adjuvant theranostic materials): another breakthrough of two-dimensional monoelemental materials (2D Xenes) as cancer nanomedicine.

Characterizing Bismuth Doping of Colloidal Germanium Quantum Dots for Energy Conversion Applications

The numerous electronic and optoelectronic applications that rely on semiconductors require tuning their properties through doping. Germanium quantum dots (Ge QDs) were successfully doped with bism...

Tunable diameter and spacing of double Ge quantum dots using highly-controllable spacers and selective oxidation of SiGe

We report the novel tunability of the diameters and spacings of paired Ge double quantum dots (DQDs) using nano-spacer technology in combination with selective oxidation of Si0.85Ge0.15 at high temperature. Pairs of spherical-shaped Ge QDs were formed by the selective oxidation of poly-SiGe spacer islands at each sidewall corner of the nano-patterned Si3N4/poly-Si ridges. The diameters of the Ge spherical QDs are essentially determined by geometrical conditions (height, width, and length) of the nano-patterned spacer islands of poly-SiGe, which are tunable by adjusting the process times of deposition and etch back for poly-SiGe spacer layers in combination with the exposure dose of electron-beam lithography. Most importantly, the separations between the Ge DQDs are controllable by adjusting the widths of the poly-Si/Si3N4 ridges and the thermal oxidation times. Our self-organization and self-alignment approach achieved high symmetry within the Ge DQDs in terms of the individual QD diameters as well as the coupling barriers between the QDs and external electrodes in close proximity.

Highly tunable doping in Ge quantum dots/graphene composite with distinct quantum dot growth evolution

Quantum dots/graphene (QDs/Gr) composites have become the research hotspot recently due to their unique synergistic effect as optical absorption material for next-generation electronic and optoelectronic devices. In this work, Ge QDs/Gr composite is prepared by a simple and effective ion-beam sputtering deposition technique. The intact growth evolution process is detailly investigated by means of the effect of Ge deposition amount, which will induce the enhanced crystallinity in QDs and the reduced defects in graphene. Moreover, a feasible and inspiring strategy to effectively tune doping in graphene by artificial control through changing the deposition amount of Ge atoms on graphene is demonstrated. In addition, charge transfer and interaction strength at the interface of Ge QD and graphene is influenced via the oxygen defect in the QD surface, which is consistent with field-effect transistor test and first-principle calculations. The p-doping characteristics of graphene decorated by Ge QDs may have significant application prospects in energy band engineering of graphene-based building blocks for graphene-based composite development and near-infrared detector applications.

Graphene quantum dots enhanced ToF-SIMS for single-cell imaging.

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) has shown promising applications in single-cell analysis owing to its high spatial resolution molecular imaging capability. One of the main drawbacks hindering progress in this field is the relatively low ionization efficiency for biological systems. The complex chemical micro-environment in single cells typically causes severe matrix effects, leading to significant signal suppression of biomolecules. In this work, we investigated the signal enhancement effect of graphene quantum dots (GE QDs) in ToF-SIMS analysis. A × 160 magnification of ToF-SIMS signal for amiodarone casted on glass slide was observed by adding amino-functionalized GE QDs (amino-GE QDs), which was significantly higher than adding previously reported signal enhancement materials and hydroxyl group-functionalized GE QDs (hydroxyl-GE QDs). A possible mechanism for GE QD-induced signal enhancement was proposed. Further, effects of amino-GE QDs and hydroxyl-GE QDs on amiodarone-treated breast cancer cells were compared. A significant signal improvement for lipids and amiodarone was achieved using both types of GE QDs, especially for amino-GE QDs. In addition, ToF-SIMS chemical mapping of single cells with better quality was obtained after signal enhancement. Our strategy for effective ToF-SIMS signal enhancement holds great potential for further investigation of drug metabolism pathways and the interactions between the cell and micro-environment.

Ion Synthesis: Si–Ge Quantum Dots

We present a method of Si–Ge QDs formation by ion beam implantation (IBI) technique and high temperature annealing for self-organization. Implantation doses varied from 1014 to 1017 cm–2, ion energies ranged from 50 to 150 keV, annealing proceeded at temperature of 950 to 1050°C in argon environment. Formed QDs show strong infrared (IR) photoluminescence (PL) in the temperature region 15–250 K.

Polymer solar cells with reduced graphene oxide–germanium quantum dots nanocomposite in the hole transport layer

Reduced graphene oxide–germanium quantum dots (rGO–Ge QDs) nanocomposite has been successfully employed in modifying poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the hole transport layer (HTL) in the preparation of a P3HT:PCBM-based polymer solar cell (PSC). The effect of the surface morphology and the optical transmittance of the PEDOT:PSS/rGO–Ge QDs HTL on the devices’ photovoltaic performance is examined. A significant improvement of up to 50% in the power conversion efficiency is achieved by the incorporation of the composite in the HTL. The modified HTL devices exhibited higher short-circuit current density values which resulted from better transportation and collection of photo-generated charge carriers. The synergistic effect of the high electrical conductivity of the composites and the formation of good ohmic contact at the interface between the anode and the active layer not only facilitates charge carrier transport but also impairs their recombination to yield better photovoltaic performance.

Ion Synthesis: Si-Ge Quantum Dots

AbstractWe present a method of Si–Ge QDs formation by ion beam implantation (IBI) technique and high temperature annealing for self-organization. Implantation doses varied from 10^14 to 10^17 cm^–2, ion energies ranged from 50 to 150 keV, annealing proceeded at temperature of 950 to 1050°C in argon environment. Formed QDs show strong infrared (IR) photoluminescence (PL) in the temperature region 15–250 K.

Growth mode of tensile-strained Ge quantum dots grown by molecular beam epitaxy

Growth mode of tensile-strained Ge quantum dots on different III–V buffers by molecular beam epitaxy is studied by a combination of reflection high-energy electron diffraction, atomic force microscopy and transmission electron microscopy. The Ge-QDs growth on the InAlAs buffer lattice matched to InP and on InAs buffer on GaSb follows the Volmer–Weber growth mode with round Ge QDs and no Ge wetting layer, while it obeys the Stranski–Krastanov growth mode on GaSb, AlSb and AlGaSb on GaSb substrates, showing rectangular shaped platelets and a clear Ge wetting layer. The discovery of the Volmer–Weber growth mode is essential to avoid forming a wetting layer and the subsequent antiphase-domain defects when capping III–Vs on Ge-QDs, important for potential optoelectronic applications.

Spectroscopic super-resolution fluorescence cell imaging using ultra-small Ge quantum dots.

We demonstrate a spectroscopic imaging based super-resolution approach by separating the overlapping diffraction spots into several detectors during a single scanning period and taking advantage of the size-dependent emission wavelength in nanoparticles. This approach has been tested using off-the-shelf quantum dots (Invitrogen Qdot) and in-house novel ultra-small (~3 nm) Ge QDs. Furthermore, we developed a method-specific Gaussian fitting and maximum likelihood estimation based on a Matlab algorithm for fast QD localisation. This methodology results in a three-fold improvement in the number of localised QDs compared to non-spectroscopic images. With the addition of advanced ultra-small Ge probes, the number can be improved even further, giving at least 1.5 times improvement when compared to Qdots. Using a standard scanning confocal microscope we achieved a data acquisition rate of 200 ms per image frame. This is an improvement on single molecule localisation super-resolution microscopy where repeated image capture limits the imaging speed, and the size of fluorescence probes limits the possible theoretical localisation resolution. We show that our spectral deconvolution approach has a potential to deliver data acquisition rates on the ms scale thus providing super-resolution in live systems.

Noise performance of high-efficiency germanium quantum dot photodetectors

We report on the noise analysis of high performance germanium quantum dot (Ge QD) photodetectors with responsivity up to ∼2 A/W and internal quantum efficiency up to ∼400%, over the 400–1100 nm wavelength range and at a reverse bias of −10 V. Photolithography was performed to define variable active-area devices that show suppressed dark current, leading to a higher signal-to-noise ratio, up to 105, and specific detectivity D*≃6×1012 cm Hz 1/2 W−1. These figures of merit suggest Ge QDs as a promising alternative material for high-performance photodetectors working in the visible to near-infrared spectral range.