Semiconductor Crystals Research Articles

A review on quantum dots and their applications

Quantum dots (QDs) are nanosized semiconductor crystals with unique chemical and physical properties, enabling them to emit bright, photobleaching-resistant light. They are classified into three categories: core type QDs, core-shell QDs, and alloyed QDs. Core-type QDs are composed of a single substance, while core-shell QDs have a semiconductor core surrounded by a shell of another semiconductor material. Alloyed QDs are manufactured using high-temperature or wet-chemical processes, while silicon-based QDs display unusual optical and electrical features due to quantum confinement forces. QDs have exceptional optoelectronic capabilities, producing photoluminescence quantum yields of up to 90%. They are useful for various applications, including optoelectronics and photocatalysis. There are three main types of QDs: colloidal, magnetic, and fluorescent. Colloidal synthesis is a widely used technique for creating QDs, offering applications in visible and near-infrared wavelengths. Magnetic QDs display unique magnetic characteristics and can be synthesized using various methods. Fluorescent QDs have high fluorescence quantum yields and are resistant to photobleaching, making them useful in imaging, sensing, and therapies. QDs are being developed to enhance biological imaging capabilities by increasing cellular uptake, reducing toxicity, and enhancing stability. They can be used for intracellular imaging, deep tissue imaging, single-molecule tracking, super-resolution imaging, targeting ligands, selective imaging of mitochondria, pH-responsive fluorescence, responding to specific cellular signals, and self-illuminating systems. However, they have limitations such as toxicity, structural instability, and deterioration due to UV light or aquatic environments.

Characterization of plasma contacts to cadmium telluride photodetector in ultrathin gas discharge cell

In the present work, the physical properties at the contact of single crystal cadmium telluride semiconductor with gas discharge plasma have been investigated. It is shown that charge carriers in the plasma, together with incident infrared radiation, contribute to the enhancement of the photocurrent in the gas discharge cell. At sufficiently high voltages (more than 2.5 kV) in the gas discharge cell, positive feedback associated with the effect of the plasma on the semiconductor surface is observed. The results of theoretical calculations and experimental experience are in satisfactory agreement, from which the physical meaning of the proportionality coefficient is determined, taking into account the plasma effect on the photoconductivity of the photodetector. The use of a double plasma contact contributes to the damping of the spatial instabilities of the photocurrents in the gas discharge cell, allowing the use of low-resistance photodetectors at the input of the device. Similar results at room temperature have been obtained for the first time on the basis of single-crystal cadmium telluride.

ИССЛЕДОВАНИЕ СКОРОСТИ УДАЛЕНИЯ ПИРОГЕННОГО SiO2 МЕТОДОМ ПЛАЗМОХИМИЧЕСКОГО ТРАВЛЕНИЯ

The study is devoted to identifying factors affecting the removal rate (etching) of pyrogenic silicon oxide (SiO2) films. The authors select the main adjustable parameters of the reactive ion plasma-chemical etching setup as external factors affecting the removal rate of pyrogenic SiO2. During the study, the authors change etching time, power, chamber pressure, gas proportion in the gas mixture, gas flow while maintaining the pressure in the chamber, and the temperature of the intra-chamber table. The paper analyzes the results of each experiment, makes the necessary calculations, provides with the graphs that clearly explain the effect of a particular external factor or its change on the rate. An optimal set of parameters for reactive ion plasma etching of pyrogenic SiO2 films is determined empirically, which one can use in the process of reverse engineering of semiconductor device crystals and structures with such oxides. In this case, removing the pyrogenic oxide film does not affect the integrity of the studied semiconductor crystals or structures.

Defect detection and size classification in CdTe samples in 3D

Defects in semiconductor crystals can have significant detrimental effects on their performance as radiation detectors. Defects cause charge trapping and recombination, leading to lower signal amplitudes and poor energy resolution. We have designed and built a modular 3D scanner for analyzing these defects in semiconductor samples using commercial off-the-shelf components. Previous solutions offer great spatial resolution, but have limited sample holding capacity and use continuum light sources which can cause difficulty differentiating between different materials within samples. Our design also includes a modular sample holder allowing for easy changing of samples. In this paper, we showcase first results achieved with this custom built scanner as well as planned developments.

A Survey of Crystals for SPECT Imaging

Single-photon emission computed tomography (SPECT) is an important nuclear medicine imaging tool for diagnosis and drug research. The gamma-ray detector is the core component of the SPECT system and influences the overall system performance. The detector crystals, which can be divided into scintillation crystals and semiconductor crystals, are among the main determinants of the detector’s performance. The development of these crystal materials plays an important role in improving SPECT imaging. This paper provides a survey of the technological development and applications of several crystals currently used in SPECT detectors. Furthermore, it explores future research directions for the development of detector crystals.

Space-Confined Vertical Growth of Large-Size Organic Semiconductor Single Crystals.

Organic semiconductor single crystals (OSSCs) have garnered considerable attention because of their high charge mobility and atomic-scale smooth surface. However, their large-size high-quality preparation remains challenging due to the inevitable defects and limited growth speed brought by traditional epitaxial growth. Here, we demonstrate a space-confined strategy, named out-of-plane microspacing in-air sublimation (OPMAS), for growing vertically millimeter-sized OSSCs in several minutes by revolutionizing the heterogeneous epitaxial growth mode severely depending on substrates into a spontaneous homogeneous growth mode free from substrates. The intrinsic driven force of this transformation is proved to be the change of surface energy, and the maximum size of crystals is thermodynamically dependent on the distance of the microspace. OPMAS has been proven to be suitable for preparing single crystals of various typical organic semiconductors. Numerous characterizations have been conducted to prove the high quality and uniformity of the thus-produced OSSCs. In addition, the photoresponse of the prepared OSSCs is highly dependent on the illumination intensities, making it suitable for high-contrast Morse coding process, demonstrating a stable switch ratio of about 3.3. This work provides a universal platform for preparing large-sized OSSCs, advancing both fundamental (opto)electronic studies and a wide range of practical applications.

Characterization and Optimization of a Locally Boron-Doped Diamond Tool for Self-sensing of Cutting Temperature

High-sensitivity and rapid-response measurements of micro zone cutting temperature are crucial for characterizing and optimizing machining states in the ultra-precision cutting process. This innovative method uses a locally boron-doped diamond (LBDD) tool itself as the sensor for in-process measurements of cutting temperature. However, the heterogeneity of boron doping and the resulting lattice distortions considerably affect the mechanical properties and temperature-sensing performances of the tool. In this work, optimized synthesis processes and structural designs for LBDD tools that function as self-sensing cutting temperature devices were proposed. Annealing treatments under high-pressure conditions were conducted to promote the diffusion and ionization of boron multimers in the boron-doped diamond zone, thereby enhancing the crystal quality and semiconductor electrical properties of the LBDD. Various LBDDs with thin-layer temperature-sensing structures of different doping concentrations and thicknesses were synthesized. The optimal components and structures were identified as the temperature-sensing cutting tool through comparative analyses of temperature measurement capabilities and semiconductor properties. The selected tool was employed for in-process cutting temperature measurement during single-point diamond turning of copper and carbon fiber. Results indicate that the LBDD tool can accurately monitor cutting temperature during steady cutting processes and identify the micromorphological features of the machined surfaces based on cutting temperature characteristics. These insights are pivotal for controlling cutting temperature and refining the ultra-precision cutting process.

Strain Engineered Semiconductor Nanomembranes for Photonic and Optoelectronic Applications

AbstractWhen semiconductor crystals are made into the form of thin sheets, i.e., nanomembranes, their properties and behaviors may be remarkably different from their bulk counterparts. A plethora of fascinating science and important applications arise consequently, some of which are investigated in recent years, and there are still a lot more to be discovered in the future. Nanomembranes (NMs) provide a good platform for strain engineering and offer tremendous research opportunities in photonics and optoelectronics applications. Strain alters energy band line up of a material furthermore influencing its carrier mobility which impacts a wide range of applications. In this article, the strain‐engineered NMs are reviewed using semiconductor materials as a model system for photonics and optoelectronics applications. While many fundamental aspects of NMs are discussed and outlined different methods for strain engineering of NM, the use of semiconductor NMs for photonics and optoelectronics applications is the locus of the present review article.

Characterization of PbMo0.3W0.7O4 Crystal: A Potential Material for Photocatalysis and Optoelectronic Applications

AbstractPbMo0.3W0.7O4 semiconductor crystal, which contains the balanced ratios of Mo and W, is grown for the first time by Czochralski method. The structural and optical properties of the crystal are investigated in detail in the present study. Structural analysis shows that crystal has tetragonal structure like PbMoO4 and PbWO4 compounds. The optical characteristics are studied by transmission, Raman, FTIR and photoluminescence methods. The bandgap energy is found to be 3.18 eV, and the positions of the conduction and valence bands are determined. The vibrational characteristics are studied by means of Raman and FTIR spectroscopy techniques. Photoluminescence spectrum presents three peaks around 486, 529, and 544 nm which fall into the green emission spectral range. Taking into account the properties of the compound, it is stated that PbMo0.3W0.7O4 (or Pb(MoO4)0.3(WO4)0.7) has the potential to be used in water splitting applications and optoelectronic devices that emit green light.

Mechanical Tuning of Fluorescence Lifetime and Bandgap in an Elastically Flexible Molecular Semiconductor Crystal.

Despite having superior transport properties, lack of mechanical flexibility is a major drawback of crystalline molecular semiconductors as compared to their polymer analogues. Here single crystals of an organic semiconductor are reported that are not only flexible but exhibit systematic tuning of bandgaps, fluorescence lifetime, and emission wavelengths upon elastically bending. Spatially resolved fluorescence lifetime imaging and confocal fluorescence microscopy reveals systematic trends in the lifetime decay across the bent crystal region along with shifts in the emission wavelength. From the outer arc to the inner arc of the bent crystal, a significant decrease in the lifetime of ≈1.9ns is observed, with a gradual bathochromic shift of ≈10nm in the emission wavelength. For the crystal having a bandgap of 2.73eV, the directional stress arising from bending leads to molecular reorientation effects and variations in the extent of intermolecular interactions- which are correlated to the lowering of bandgap and the evolution of the projected density of states. The systematic changes in the interactions quantified using electron density topological analysis in the compressed inner arc and elongated outer arc region are correlated to the non-radiative decay processes, thus rationalizing the tuning of fluorescence lifetime.

Low energy dark matter searches

This paper summarizes the motivations and challenges for direct detection experiments aimed at dark matter particles with masses below the GeV scale. Two such experiments with large Canadian contributions, currently operating or under construction at SNOLAB, are discussed in detail: SuperCDMS, which employs cryogenic semiconductor crystals, and NEWS-G, which employs noble gas spherical detectors. Finally, we highlight recent efforts to investigate sharply rising event rates below a few hundred eV, in excess of expectations from existing background models, that have been observed in multiple direct detection experiments.

Ag nanoparticles at p-Si/ MAPbI3 perovskite interface: improved photo responsivity and response speed in photodetection

Although enhanced performances of photovoltaic devices by embedding metal nanoparticals in charge transport layer, doping into active layer bulk, decorating the active layer surface, and inserting at the interface between semiconductor and the electrode were reported, the effect of incorporating metal NPs at the interface of single crystal semiconductor and perovskite is rarely tackled. Herein the effects of incorporating Ag nanoparticals (AgNPs) at p-Si/MAPbI3 perovskite interface on the photodiode performances were investigated. The results showed that compared with reference device (without AgNPs) the photoresponsivity of the device incorporating AgNPs is greatly improved with the exception for light with wavelengths fall in the spectral range where AgNPs have strong optical absorption. This effect is extremely significant for relatively shorter wavelengths in visible region, and a maximal improvement of around 10.6 times in photoresponsivity was achieved. The physical origin of the exception for spectral range that AgNPs have strong optical absorption is the cancelation of scatter resulted enhancement through AgNPs by band-to-band absorption resulted reduction of photocurrent, in which the generated electron has energy near the fermi level and the hole has large effective mass, which relax by nonradiative recombination, thus making not contribution to the photocurrent. More importantly, the AgNP decorated device showed much faster photo response speed than reference device, and a maximal improvement of around 7.9 times in rise and fall time was achieved. These findings provide a novel approach for high responsive and high speed detection for weak light.

Modeling the melting temperature of semiconductor nanocrystals

Exploring the thermal stability of semiconductor crystals at the nanoscale is of great significance for the design, fabrication, and application of modern quantum devices. In this paper, we propose a thermodynamic model to predict the melting temperature of semiconductor nanocrystals, which is in good agreement with the experimental results of Si, Bi, CdS, and CdSe. In addition, when the size decreases, the drop of melting temperature curves tends to be synchronized with the size-dependent solid/liquid interface energy and surface stress ratio γsl(D)/f(D), which reveals the physical origin of the decrease in the melting temperature of the semiconductor nanocrystals.

Cation-eutaxy-enabled III-V-derived van der Waals crystals as memristive semiconductors.

Novel two-dimensional semiconductor crystals can exhibit diverse physical properties beyond their inherent semiconducting attributes, making their pursuit paramount. Memristive properties, as exemplars of these attributes, are predominantly manifested in wide-bandgap materials. However, simultaneously harnessing semiconductor properties alongside memristive characteristics to produce memtransistors is challenging. Herein we prepared a class of semiconducting III-V-derived van der Waals crystals, specifically the HxA1-xBX form, exhibiting memristive characteristics. To identify candidates for the material synthesis, we conducted a systematic high-throughput screening, leading us to 44 prospective III-V candidates; of these, we successfully synthesized ten, including nitrides, phosphides, arsenides and antimonides. These materials exhibited intriguing characteristics such as electrochemical polarization and memristive phenomena while retaining their semiconductive attributes. We demonstrated the gate-tunable synaptic and logic functions within single-gate memtransistors, capitalizing on the synergistic interplay between the semiconducting and memristive properties of our two-dimensional crystals. Our approach guides the discovery of van der Waals materials with unique properties from unconventional crystal symmetries.

Characterization of composition dependence of properties of a MgNiO-based MSM structure

In this study, the effect of Mg composition on structural and optical properties of MgxNi1-xO alloy thin film single crystal semiconductors as well as their implementation into Metal-Semiconductor–Metal (MSM) photodetector are studied. An 850 meV blue-shift of the bandgap is observed from 3.65 eV to 4.50 eV with increasing Mg composition from 0% to 67%. The deep ultraviolet/visible rejection ratio, which is the ratio of photosensitivity at a peak wavelength of 360 nm to that at 450 nm is found to be ∼58 for Mg composition of 67%. Mg rich (%67 Mg) alloy-based photodetector is found to have two orders smaller dark current and have higher spectral response compared to NiO-based one. Spectral responsivities for MgxNi1-xO photodetectors are determined as 415 mA W−1, 80 mA W−1, and 5.6 mA W−1 for Mg compositions of 67%, 21%, and 0% (reference-NiO), respectively. Furthermore, the detectivity of the photodetectors enhances as Mg composition increases and the highest detectivity of a magnitude of ∼1011 Jones is found for the photodetector with Mg composition of 67%.

Metal-Organic Framework with Dual Excitation Pathways as Efficient Bifunctional Catalyst for Photo-assisted Li-O2 Batteries.

Li-O2 batteries (LOBs) have sparked significant interest due to their fascinating high theoretical energy density. However, the large overpotential for the formation and oxidation of Li2O2 during charge and discharge process seriously hinders the further development and application of LOBs. In this work, metal-organic frameworks (MOFs) with different metal clusters (Fe, Ti, Zr) are successfully synthesized, and they are employed as the photoelectrodes for the photo-assisted LOBs. The special dual excitation pathways of Fe-MOF under illumination and the superior separation efficiency of photocarriers, which significantly enhance the activation of O2/Li2O2, improving the catalytic activity of oxygen reduction reaction and oxygen evolution reaction. Moreover, compared to traditional inorganic semiconductor crystals, Fe-MOF exhibits large specific surface area and excellent O2 adsorption ability. Therefore, the LOB with Fe-MOF as the cathode exhibits large specific capacity, ultralow charge/discharge overpotential of 0.22V at 0.05mA cm-2 and excellent stability of 195 cycles under illumination. This study provides an environmentally friendly and highly efficient photocatalyst for LOBs, and a new strategy for designing photoelectrodes.

A meta-analysis of semiconductor materials fabricated in microgravity

This meta-analysis of 160 semiconductor crystals that were grown in microgravity on orbital vehicles between 1973 and 2016 is based on publicly available information documented in the literature. This analysis provides comparisons of crystal metrics including size, structure quality, uniformity, and improved performance between crystals grown in microgravity or terrestrially. Improvement in at least one of these metrics was observed for 86% of those materials that included data in their studies.

Vertical field‐effect transistor using c‐axis aligned crystal indium–gallium–zinc oxide on glass substrate and prototype organic light‐emitting diode display

AbstractThis study developed a technology for a vertical field‐effect transistor (VFET) incorporating c‐axis aligned crystal oxide semiconductor on a Gen 3.5 glass substrate. VFETs, with a channel length of 0.5 μm, demonstrated stable characteristics with minimal variation, higher on‐state current compared with low‐temperature polysilicon FETs, and extremely low off‐state leakage current. A prototype 513‐ppi organic light‐emitting diode display that features a red, green, and blue stripe arrangement and includes an internal compensation circuit with a configuration of six transistors and two capacitors was fabricated by harnessing the advantageous features of VFETs. Such a display was previously unattainable with planar FETs. Thus, the developed VFET technology presents a viable pathway for achieving ultrahigh‐resolution panels on glass substrates.

Complete photonic bandgap in a low-index two-dimensional quasicrystalline structure.

A bandgap in the continuum spectrum of photons in addition to its basic physical significance has strong potential for applications. Analogous to semiconductor crystals for electrons, periodic dielectric structures named photonic crystals were proposed to control photon flux propagation. In our search for low refractive index (RI) structures with a photonic bandgap, initial research efforts were focused on photonic crystal design, while aperiodic structures allow lower values of refractive index contrast to sustain a photonic bandgap. Here, we report on a two-dimensional quasicrystalline structure designed as a set of one-dimensional lattices merged into a single binary structure made of two materials with refractive index contrast 2|n1 - n2|/(n1 + n2) = 0.16 and even less in theory. We confirmed the theoretical prediction of bandgap exciting by measuring the radiation suppression of a dipole source placed in the center of the quasicrystalline structure. The full-wave numerical simulations and the experimental study appear to be in good agreement with the theoretical model.

Charge redistribution of a spatially differentiated ferroelectric Bi4Ti3O12 single crystal for photocatalytic overall water splitting

Artificial photosynthesis is a promising approach to produce clean fuels via renewable solar energy. However, it is practically constrained by two issues of slow photogenerated carrier migration and rapid electron/hole recombination. It is also a challenge to achieve a 2:1 ratio of H2 and O2 for overall water splitting. Here we report a rational design of spatially differentiated two-dimensional Bi4Ti3O12 nanosheets to enhance overall water splitting. Such a spatially differentiated structure overcomes the limitation of charge transfer across different crystal planes in a single crystal semiconductor. The experimental results show a redistribution of charge within a crystal plane. The resulting photocatalyst produces 40.3 μmol h–1 of hydrogen and 20.1 μmol h–1 of oxygen at a near stoichiometric ratio of 2:1 and a solar-to-hydrogen efficiency of 0.1% under simulated solar light.