Single-crystalline Semiconductor Research Articles

High-performance single-crystalline In2O3 field effect transistor toward three-dimensional large-scale integration circuits

Formation of a single crystalline oxide semiconductor on an insulating film as a channel material capable of three-dimensional (3D) stacking would enable 3D very-large-scale integration circuits. This study presents a technique for forming single-crystalline In2O3 having no grain boundaries in a channel formation region on an insulating film using the (001) plane of c-axis-aligned crystalline indium gallium zinc oxide as a seed. Vertical field-effect transistors using the single-crystalline In2O3 had an off-state current of 10−21 A μm−1 and electrical characteristics were improved compared with those using non-single-crystalline In2O3: the subthreshold slope was improved from 95.7 to 86.7 mV dec.−1, the threshold voltage showing normally-off characteristics (0.10 V) was obtained, the threshold voltage standard deviation was improved from 0.11 to 0.05 V, the on-state current was improved from 22.5 to 28.8 μA, and a 17-digit on/off ratio was obtained at 27 °C.

Effects of UV/O3 and O2 plasma surface treatments on the band-bending of ultrathin ALD-Al2O3 coated Ga-polar GaN

The recently demonstrated semiconductor grafting approach allows one to create an abrupt, low interface-trap-density heterojunction between a high-quality p-type single-crystalline semiconductor (non-nitrides) with n-type GaN. However, due to the surface band-bending from GaN polarization, an energy barrier exists at the grafted heterojunction, which can impact the vertical charge carrier transport. Reducing the energy barrier height is essential for some advanced device development. In this work, we employed UV/O3 and O2 plasma to treat a Ga-polar GaN surface with/without an ultrathin (∼2 nm) ALD-Al2O3 coating and studied the effects of the treatments on surface band-bending. Through XPS measurements, it was found that the treatments can suppress the upward band-bending of the Ga-polar GaN by 0.11–0.39 eV. The XPS results also showed that UV/O3 treatment is an effective surface cleaning method with little surface modification, while O2 plasma causes a strong oxidation process that occurs inside the top layer GaN.

Heavy-to-light electron transition enabling real-time spectra detection of charged particles by a biocompatible semiconductor

The current challenge of wearable/implantable personal dosimeters for medical diagnosis and radiotherapy applications is lack of suitable detector materials possessing both excellent detection performance and biocompatibility. Here, we report a solution-grown biocompatible organic single crystalline semiconductor (OSCS), 4-Hydroxyphenylacetic acid (4HPA), achieving real-time spectral detection of charged particles with single-particle sensitivity. Along in-plane direction, two-dimensional anisotropic 4HPA exhibits a large electron drift velocity of 5 × 105 cm s−1 at “radiation-mode” while maintaining a high resistivity of (1.28 ± 0.003) × 1012 Ω·cm at “dark-mode” due to influence of dense π-π overlaps and high-energy L1 level. Therefore, 4HPA detectors exhibit the record spectra detection of charged particles among their organic counterparts, with energy resolution of 36%, (μt)e of (4.91 ± 0.07) × 10−5 cm2 V−1, and detection time down to 3 ms. These detectors also show high X-ray detection sensitivity of 16,612 μC Gyabs−1 cm−3, detection of limit of 20 nGyair s−1, and long-term stability after 690 Gyair irradiation.

(Invited) Applications of Electrochemistry Toward Blue/Green and SWIR-Wavelength VCSELs

Unlike the more established edge-emitting lasers (EELs) with a horizontal Fabry-Perot (FB) cavity, VCSELs have a vertical cavity with highly reflective top and bottom mirrors sandwiching the active region. This design enables wafer-level testing, one- and two-dimensional arrayed integration, and scalability for low- and high-power applications. VCSELs are poised to surpass EELs as a more versatile and intelligent option for semiconductor lasers in the future.Currently commercially available VCSELs only cover the red to near-infrared (NIR) range of 700-1100nm, whereas EELs offer products across a wide spectral range. The optimal active regions for blue and short-wavelength infrared (SWIR) spectra are only supported on GaN and InP substrates, respectively. Lattice-matched, epitaxial mirrors compatible with these two substrates remain major challenges. As a solution, we propose the use of electrochemistry to engineer the refractive index of the material. The innovation is based on the recognition that nanoporous (NP) semiconductor layers can be considered a nanocomposite with nanoscale voids of air uniformly dispersed in a single-crystalline semiconductor, thus rendering a unique way to control the effective optical index with a tunability that is typically un-attainable through epitaxy.We have studied the electrochemistry of semiconductors for applications in photonics, beginning with GaN and most recently with InP. In both material systems, we have discovered a selective porosification process based on the doping concentration. Due to the doping selectivity in EC etching, layers with high doping concentration will be converted to low index nanoporous material with an unprecedented tunability in the refractive index depending on the porosity. Meanwhile, the lightly doped layers remain intact. As a result, highly reflective mirrors were fabricated on GaN and InP substrates with wide stopbands. In this talk, we will provide latest updates in the VCSEL performances in the blue/green and long-wavelength region.

Thermal conductivity of group IV elemental semiconductors

The thermal conductivity of group IV elements—germanium, silicon, and diamond—is described in order to demonstrate various important and interesting aspects of the mechanism of phonon heat transfer in single-crystalline semiconductors and dielectrics. The measured temperature dependence of thermal conductivity κ(T) for these materials reveals different phonon scattering processes that determine thermal conductivity. In addition to the intrinsic processes of phonon–phonon scattering, scattering by isotopes, dopants, free electrons, sample surfaces, the effects of phonon focusing, irradiation with high-energy particles, and phonon hydrodynamics are discussed.

Self-Rolled-Up Ultrathin Single-Crystalline Silicon Nanomembranes for On-Chip Tubular Polarization Photodetectors.

Freestanding single-crystalline nanomembranes and their assembly have broad application potential in photodetectors for integrated chips. However, the release and self-assembly process of single-crystalline semiconductor nanomembranes still remains a great challenge in on-chip processing and functional integration, and photodetectors based on nanomembrane always suffer from limited absorption of nanoscale thickness. Here, a non-destructive releasing and rolling process is employed to prepare tubular photodetectors based on freestanding single-crystalline Si nanomembranes. Spontaneous release and self-assembly are achieved by residual strain introduced by lattice mismatch at the epitaxial interface of Si and Ge, and the intrinsic stress and strain distributions in self-rolled-up Si nanomembranes are analyzed experimentally and computationally. The advantages of light trapping and wide-angle optical coupling are realized by tubular geometry. This Si microtube device achieves reliable Ohmic contact and exhibits a photoresponsivity of over 330mA W-1 , a response time of 370 µs, and a light incident detection angle range of over 120°. Furthermore, the microtubular structure shows a distinct polarization angle-dependent light absorption, with a dichroic ratio of 1.24 achieved at 940nm. The proposed Si-based microtubes provide new possibilities for the construction of multifunctional chips for integrated circuit ecosystems in the More than Moore era.

Room-temperature ferromagnetism in Fe-doped SnSe bulk single crystalline semiconductor

The quest for pragmatic room-temperature (RT) magnetic semiconductors (MSs) with a suitable bandgap constitutes one of the contemporary opportunities to be exploited. This may provide a materials platform for to bring new-generation ideal information device technologies into real-world applications where the otherwise conventionally separately utilized charge and spin are simultaneously exploited. Here we present RT ferromagnetism in an Fe-doped SnSe (Fe:SnSe) van der Waals (vdW) single crystalline ferromagnetic semiconductor (FMS) with a semiconducting bandgap of ∼1.19 eV (comparable to those of Si and GaAs). The synthesized Fe:SnSe single crystals feature a dilute Fe content of <1.0 at%, a Curie temperature of ∼310 K, a layered vdW structure nearly identical to that of pristine SnSe, and the absence of in-gap defect states. The Fe:SnSe vdW diluted magnetic semiconductor (DMS) single crystals are grown using a simple temperature-gradient melt-growth process, in which the magnetic Fe atom doping is realized uniquely using FeI2 as the dopant precursor whose melting point is low with respect to crystal growth, and which in principle possesses industrially unlimited scalability. Our work adds a new member in the family of long-searching RT magnetic semiconductors, and may establish a generalized strategy for large-volume production of related DMSs.

Driving dislocation motion in ZnS single-crystalline semiconductor for extraordinary mechano-electro-optical properties

Driving dislocation motion in ZnS single-crystalline semiconductor for extraordinary mechano-electro-optical properties

Long-distance transport of hot carriers due to acoustic phonon bottleneck in PbSe with room-temperature sensitive mid-infrared sensing

In the optoelectronic conversion process of semiconductors, the photo-excited carriers with energy higher than energy band edge, i.e., hot carriers, have always fast (picoseconds scale) dissipated within 100 nanometers distance through lattice scattering. Specifically, the hot carriers relaxation accounts for more than 60% energy loss in narrow bandgap semiconductor. Herein, we observe an ultralong transport of hot carriers (558 nm) by local light excitation in single-crystalline thermoelectric semiconductor PbSe via the time-resolved reflectivity dynamics. The ultraweak phonon emission of PbSe results in a long-distance thermalized carriers transport due to acoustic phonon bottleneck. Furthermore, the hot carriers effect gives rise to a self-driven (zero bias), fast (900 ns), and sensitive (D* = 1.1 × 1010 cm Hz1/2 W−1 at 3.3 μm) mid-infrared detection and imaging at room temperature. Our discovery provides an insight into optoelectronic conversion mechanism of narrow bandgap thermoelectric semiconductors with intriguing optoelectronic applications.

Single-atomic-site platinum steers photogenerated charge carrier lifetime of hematite nanoflakes for photoelectrochemical water splitting

Although much effort has been devoted to improving photoelectrochemical water splitting of hematite (α-Fe2O3) due to its high theoretical solar-to-hydrogen conversion efficiency of 15.5%, the low applied bias photon-to-current efficiency remains a huge challenge for practical applications. Herein, we introduce single platinum atom sites coordination with oxygen atom (Pt-O/Pt-O-Fe) sites into single crystalline α-Fe2O3 nanoflakes photoanodes (SAs Pt:Fe2O3-Ov). The single-atom Pt doping of α-Fe2O3 can induce few electron trapping sites, enhance carrier separation capability, and boost charge transfer lifetime in the bulk structure as well as improve charge carrier injection efficiency at the semiconductor/electrolyte interface. Further introduction of surface oxygen vacancies can suppress charge carrier recombination and promote surface reaction kinetics, especially at low potential. Accordingly, the optimum SAs Pt:Fe2O3-Ov photoanode exhibits the photoelectrochemical performance of 3.65 and 5.30 mA cm−2 at 1.23 and 1.5 VRHE, respectively, with an applied bias photon-to-current efficiency of 0.68% for the hematite-based photoanodes. This study opens an avenue for designing highly efficient atomic-level engineering on single crystalline semiconductors for feasible photoelectrochemical applications.

Ferroelectric Nitride Heterostructures on CMOS Compatible Molybdenum for Synaptic Memristors.

Achieving ferroelectricity in III-nitride (III-N) semiconductors by alloying with rare-earth elements, e.g., scandium, has presented a pivotal step toward next-generation electronic, acoustic, photonic, and quantum devices and systems. To date, however, the conventional growth of single-crystalline nitride semiconductors often requires the use of sapphire, Si, or SiC substrate, which has prevented their integration with the workhorse complementary metal oxide semiconductor (CMOS) technology. Herein, we demonstrate single-crystalline ferroelectric nitride semiconductors grown on CMOS compatible metal-molybdenum. Significantly, we find that a unique epitaxial relationship between wurtzite and body-centered cubic crystal structure can be well maintained, enabling the realization of single-crystalline wurtzite ferroelectric nitride semiconductors on polycrystalline molybdenum that was not previously possible. Robust and wake-up-free ferroelectricity has been measured, for the first time, in the epitaxially grown ScAlN directly on metal. We further propose and demonstrate a ferroelectric GaN/ScAlN heterostructure for synaptic memristor, which shows the capability of emulating the spike-time-dependent plasticity in a biological synapse. This work provides a viable path for the integration of III-N architectures with the mature CMOS technology and sheds light on the promising applications of ferroelectric nitride memristors in neuromorphic computing.

Intercalation of p-Aminopyridine and p-Ethylenediamine Molecules into Orthorhombic In1.2Ga0.8S3 Single Crystals

A single crystalline layered semiconductor In1.2Ga0.8S3 phase was grown, and by intercalating p-aminopyridine (NH2-C5H4N or p-AP) molecules into this crystal, a new intercalation compound, In1.2Ga0.8S3·0.5(NH2-C5H4N), was synthesized. Further, by substituting p-AP molecules with p-ethylenediamine (NH2-CH2-CH2-NH2 or p-EDA) in this intercalation compound, another new intercalated compound-In1.2Ga0.8S3·0.5(NH2-CH2-CH2-NH2) was synthesized. It was found that the single crystallinity of the initial In1.2Ga0.8S3 samples was retained after their intercalation despite a strong deterioration in quality. The thermal peculiarities of both the intercalation and deintercalation of the title crystal were determined. Furthermore, the unit cell parameters of the intercalation compounds were determined from X-ray diffraction data (XRD). It was found that increasing the c parameter corresponded to the dimension of the intercalated molecule. In addition to the intercalation phases' experimental characterization, the lattice dynamical properties and the electronic and bonding features of the stoichiometric GaInS3 were calculated using the Density Functional Theory within the Generalized Gradient Approximations (DFT-GGA). Nine Raman-active modes were observed and identified for this compound. The electronic gap was found to be an indirect one and the topological analysis of the electron density revealed that the interlayer bonding is rather weak, thus enabling the intercalation of organic molecules.

Self-powered photodetectors based on InxMo1-xS2 crystals

Transition metal dichalcogenides (TMDCs) have attracted global interest in recent years due to their optoelectronic characteristics and tunable bandgap energies. Due to their potential use in photovoltaic devices, photodetectors, and field effect transistor (FET) recording systems, single crystalline semiconductors of TMDC family have attracted a lot of attention. In the present article, the direct vapour transport technique was used to synthesis the InxMo1-xS2 (x = 0, 0.05, and 0.1) crystals. The purity and distribution of all the elements were investigated by EDAX mapping. The power X-ray diffraction technique examine the grown crystals have hexagonal lattice structure. The structure of all the crystals was investigated by scanning electron microscopy (SEM). The in-plane E2g and outer-plane A1g vibration modes were studied through Raman spectra. Photodetectors based on InxMo1-xS2(x = 0, 0.05, and 0.1) crystals show the self-powered photoresponse under white light source at 100 mW/cm2power intensity.

Time-domain thermoreflectance (TDTR) data analysis using phonon hydrodynamic model

Time-domain thermoreflectance (TDTR) is a powerful pump–probe technique for measuring thermal properties of materials and interface thermal conductance. However, a diffusive thermal transport model is often used for data analysis, leading to underestimated thermal conductivities for high thermal conductivity materials, for example, single-crystalline semiconductors like Si at low temperatures. In this work, we have developed a theoretical model based on phonon hydrodynamics, an approximation of the phonon Boltzmann transport equation, for TDTR data analysis. We apply this model to process the TDTR signals of Si measured between 80 and 300 K. The extracted thermal conductivities using the phonon hydrodynamic model agree remarkably well with the bulk values measured by the steady-state technique, providing a more appropriate way of TDTR data analysis. The effectiveness of the phonon hydrodynamic model is further verified by analyzing TDTR signals of Ge at room temperature.

Investigation of effective stress imposed on flexible single-crystalline semiconductor nanomembrane electronics under bending conditions

Flexible electronics have gained attention with their unique ability to withstand stress deformations. However, stress makes significant impact on the electrical performance of the flexible devices. It is commonly believed that the stress imposed on the flexible device is only related to the bending curvature. Our study shows that the actual stress imposed on the device is not only related to the bending radius but also closely related to the device dimension. In this study, the effective stress of the device layer as well as the stress distributions are investigated, with the fundamental flexible diodes as representative examples. Flexible single-crystalline silicon [Formula: see text]-[Formula: see text]-[Formula: see text] diodes are fabricated and measured under different bending curvature conditions. Then the dominant affecting factor of the flexible diodes with bending stress is extracted. 3D finite-element method (3D-FEM) stress distribution modeling is also employed to analyze the stress distributions and demonstrate that the effective stress of the device layer is closely and proportionally related to the device dimension. Furthermore, theoretical calculations are conducted to verify the FEM results and quantitatively show the relation between the stress and the dimension of the flexible devices. The analysis provides a guideline in the design of flexible electronics under bending conditions.

Polarization‐Driven‐Orientation Selective Growth of Single‐Crystalline III‐Nitride Semiconductors on Arbitrary Substrates (Adv. Funct. Mater. 14/2022)

Arbitrary Substrates In article number 2113211, Xuelin Yang, Bing Huang, Bo Shen, and co-workers propose a strategy of polarization-driven-orientation selective growth and demonstrate that single-crystalline GaN can in principle be achieved on polycrystalline diamond or other substrates by utilizing a composed buffer layer consisting of graphene and polycrystalline physical-vapor-deposited AlN. This strategy can be extended to the growth of any emergent single-crystalline semiconductor films on any arbitrary freestanding substrates by choosing appropriate 2D materials with matched crystal structures.

Layer-resolved release of epitaxial layers in III-V heterostructure via a buffer-free mechanical separation technique.

Layer-release techniques for producing freestanding III-V epitaxial layers have been actively developed for heterointegration of single-crystalline compound semiconductors with Si platforms. However, for the release of target epitaxial layers from III-V heterostructures, it is required to embed a mechanically or chemically weak sacrificial buffer beneath the target layers. This requirement severely limits the scope of processable materials and their epi-structures and makes the growth and layer-release process complicated. Here, we report that epitaxial layers in commonly used III-V heterostructures can be precisely released with an atomic-scale surface flatness via a buffer-free separation technique. This result shows that heteroepitaxial interfaces of a normal lattice-matched III-V heterostructure can be mechanically separated without a sacrificial buffer and the target interface for separation can be selectively determined by adjusting process conditions. This technique of selective release of epitaxial layers in III-V heterostructures will provide high fabrication flexibility in compound semiconductor technology.

Scalable Single-Crystalline Organic 1D Arrays for Image Sensor.

Optoelectronic applications of organic semiconductors demand single-crystalline structures with long-range order and suppressed defects for sustaining efficient carrier transport and long photocarrier lifetime, which are pivotal in photodetection, photovoltaic, and light emission. For integrated devices, an additional requirement of precise patterning is imposed, whereas the patterning of single-crystalline organic microstructures is still challenging because the molecular stacking is easily perturbed by disordered fluids in microdroplets. Herein, a capillary-bridge lithography is developed for driving the directional transport of capillary flows to control the confined crystallization of organic 1D single-crystalline arrays with aligned positioning and pure orientation. Through tuning the concentration and pressure, the size of organic 1D arrays in three dimensions can be controlled with 2.9-5.8µm in width and 1.2µm to 110nm in height. Organic 1D array photodetectors exhibit a stable performance with on/off ratio of 180 and responsivity of 4.99mA W-1 . Based on the scalable fabrication of 1D array photodetectors, 20 × 20 multiplexed image sensors with high accuracy are demonstrated for capturing the light signals of capital letter "A," "B," and "C." This research will open opportunities for the large-scale fabrication of organic single-crystalline semiconductors toward the integrated optoelectronic modules.

Controllable molecular doping in organic single crystals toward high-efficiency light-emitting devices

Organic single-crystalline semiconductors have drawn significant attention in the area of organic electronic and optoelectronic devices due to their superiorities of highly ordered structure, high carrier mobility and low impurity content. Molecular doping technique has made great progress in improving device performance via optimizing the optical and electrical properties of organic semiconductors. In particular, this technique has been attempted by taking fluorescent dye-molecules as the emissive dopants to tune emission color and improve device performance of organic single crystals. Up to now, there are few reports about the use of molecular doping in organic single crystals to optimize their intrinsic electrical properties. Here, we have introduced the controllable molecular doping as a feasible approach toward manipulating charge carrier transport properties of organic single crystals. Upon optimization of doping concentration, balanced carrier transport can be realized in 5,5′-bis(4-trifluoromethyl phenyl) [2,2’] bithiophene (P2TCF3)-doped 1,4-bis(4-methylstyryl) benzene (BSB–Me) crystals. Organic light-emitting devices (OLEDs) based on these doped crystals achieve a maximum luminance of 423 cd/m2 and current efficiency of 0.48 cd/A. It demonstrates that high-efficiency crystal-based OLEDs are of great significance for the development of organic electronics, especially for display and lighting applications.

A review on the role of emerging revolutionary nanotechnology in forensic investigations

Due to the unique properties of nanoparticles, it has gained prominence in lots of fields with extensive research being carried around it. With lots of novel applications arising from this field, Forensic science seems to be one of the fast-growing fields in nano research applications. The growing and extensive use of nanotechnology being applied in forensic investigations is promising and could soon be the tipping point in the discipline. Applications mainly have been related to evidence identification and analysis in the broad major fields in Forensic Science such as single-crystalline semiconductor CdS nano slabs for explosives detection, functionalized TiO2 nanorods for organophosphorus chemical warfare agents in Forensic Chemistry, the use of Nanopowders for latent print visualization in Forensic physics and Gold nanoparticle protein nanopore for detection of single-stranded DNA in Forensic biology. Nanotechnology has also been employed in illegal drug detection in recent times. These and other applications of Nanotechnology provides prompt and precise results with reduced methods due to the limited instruments used for analyzing evidence as well as providing sensitive and selective ways of detecting evidence. As evidence is notable in forensic investigations, nanotechnology’s use in identifying and detecting these has potential in enhancing and providing efficient and rapid means for investigations and unravelling leads into crimes. This review emphasizes some disciplines in forensic sciences in which nanotechnology is having an impact, novel methods and newly developed instruments and also takes into account its challenges as well as perspectives into the future.