Semiconductor Single Crystals Research Articles

Neutron Imaging with Timepix Coupled Lithium Indium Diselenide

The material lithium indium diselenide, a single crystal neutron sensitive semiconductor, has demonstrated its capabilities as a high resolution imaging device. The sensor was prepared with a 55 μ m pitch array of gold contacts, designed to couple with the Timepix imaging ASIC. The resulting device was tested at the High Flux Isotope Reactor, demonstrating a response to cold neutrons when enriched in 95% 6 Li. The imaging system performed a series of experiments resulting in a <200 μ m resolution limit with the Paul Scherrer Institute (PSI) Siemens star mask and a feature resolution of 34 μ m with a knife-edge test. Furthermore, the system was able to resolve the University of Tennessee logo inscribed into a 3D printed 1 cm 3 plastic block. This technology marks the application of high resolution neutron imaging using a direct readout semiconductor.

A theoretical approach for simulations of anisotropic charge carrier mobility in organic single crystal semiconductors

Abstract Charge carrier mobility is important for organic semiconductor materials and mainly determines their device performance. Thereby how to improve carrier mobility lies at the heart of the development of organic electronics. Theoretical predictions and simulations can provide guidelines towards the possible realization of high mobility and the design of highly functional semiconductor materials and thus can help to achieve further discoveries in the field. In this paper, we review a recently proposed theoretical method (an effective one-dimensional diffusion equation model) which presents the first analytical expression for angular resolution anisotropic mobility of organic single crystal semiconductors. The method encompasses the hopping mechanism, Marcus-Hush theory and first-principles calculations and is suitable to characterizing the anisotropic transport behaviors in organic single crystal semiconductors as well as to studying the property-structure relationship in semiconductor materials. Illustration of applications of the method demonstrated its capabilities in description and understanding of the transport of charges, correct prediction of angular resolution anisotropic mobility, and assist in the design of n-type and p-type organic electronic materials.

Evolution of Models and Algorithms for Calculating the Parameters of Technological Processes to Obtain Materials for Micro- and Nanoelectronics

The results of creating a system of models and algorithms for calculating the parameters of technological processes for obtaining materials of micro- and nanoelectronics and designing equipment are considered. It is shown that the distinctive feature of the teaching methods for special technological courses in electronic engineering materials is the construction of courses by analogy with the technological processes for obtaining materials for electronics: from a bulk single crystal to instrumental structures, whose dimensions do not currently exceed several tens of nanometers. A scientific model approach to the solution of technological problems was formed in the study of heat and mass transfer processes, which together with the processes of interaction in liquids and gas, taking heterogeneous reactions into account, are the theoretical basis of the technology of electronic engineering materials. The possibilities of physical and mathematical modeling are compared. Approaches to create mathematical models of the growth processes of single crystals of semiconductors, epitaxial layers, and heterostructures are considered and the possibilities of their practical use are determined. It is determined that the ideas proposed by V.V. Krapukhin at the initial stages of training specialists in the field of the technology of electronic material and developed by his students identified the possibility of training several generations of qualified specialists.

Low-Temperature Hydrothermal Synthesis of Colloidal Crystal Templated Nanostructured Single-Crystalline ZnO

Single crystal semiconductors almost always exhibit better optoelectrical properties than their polycrystalline or amorphous counterparts. While three-dimensionally (3D) nanostructured semiconductor devices have been proposed for numerous applications, in the vast majority of reports, the semiconductor is polycrystalline or amorphous, greatly reducing the potential for advanced properties. While technologies for 3D structuring of semiconductors via use of a 3D template have advanced significantly, approaches for epitaxially growing nanostructured single crystal semiconductors within a template remain limited. Here, we demonstrate the epitaxial growth of 3D-structured ZnO through colloidal templates formed from 225 and 600 nm diameter colloidal particles via a low-temperature (∼80 °C) hydrothermal process using a flow reactor. The effects of the pH of the reaction solution as well as the additive used on the 3D epitaxy process are investigated. The optical and electrical properties of the epitaxially grown...

A new electrode design for ambipolar injection in organic semiconductors

Organic semiconductors have attracted much attention for low-cost, flexible and human-friendly optoelectronics. However, achieving high electron-injection efficiency is difficult from air-stable electrodes and cannot be equivalent to that of holes. Here, we present a novel concept of electrode composed of a bilayer of tetratetracontane (TTC) and polycrystalline organic semiconductors (pc-OSC) covered by a metal layer. Field-effect transistors of single-crystal organic semiconductors with the new electrodes of M/pc-OSC/TTC (M: Ca or Au) show both highly efficient electron and hole injection. Contact resistance for electron injection from Au/pc-OSC/TTC and hole injection from Ca/pc-OSC/TTC are comparable to those for electron injection from Ca and hole injection from Au, respectively. Furthermore, the highest field-effect mobilities of holes (22 cm2 V–1 s–1) and electrons (5.0 cm2 V–1 s–1) are observed in rubrene among field-effect transistors with electrodes so far proposed by employing Ca/pc-OSC/TTC and Au/pc-OSC/TTC electrodes for electron and hole injection, respectively.

Spectroscopy of Excitons in Heterostructures with Quantum Dots

We consider the appearance of a new type of electronic excitation in heterostructures with semiconductor and dielectric quantum dots: excitons formed by spatially separated electrons and holes. We have observed the effect of a substantial increase in the binding energy of such an exciton (the hole moves within the quantum dot, while the electron is localized above the spherical surface of the quantum dot–matrix interface) in nanosystems containing semiconductor and dielectric quantum dots, compared with the binding energy of an exciton in semiconductor and dielectric single crystals.

Method for additional purification of the surface of Si(111) single crystal

A method for additional purification of the surface of single crystals of semiconductors is developed, which consists in the preliminary cleaning of samples by thermal heating in combination or without ion etching in ultrahigh vacuum, followed by implantation with low-energy Ba+ ions (or ions of other alkaline elements) and their successive removal by brief (1 min) high-temperature (T = 1550 K) thermal heating. The effect of additional purification is achieved by the fact that the embedded ions of Ba+ or other alkaline elements, being active, form compounds with impurity atoms (O, C, S, N, etc.) and are removed during hightemperature heating.

Single-photon superradiant decay of cyclotron resonance in a p -type single-crystal semiconductor film with cubic structure

We study a single-photon super-radiance under the conditions of cyclotron resonance in a perfect single-crystal p-type semiconductor film with cubic structure. We show that the rate of super-radiant emission scales with tjhe film area. which allows one to specify the size of the film at which the probability of a single-photon super-radiance becomes much greater than the probabilities of other scattering channels. The power of super-radiant emission depends only on three fundamental constants: the electron charge q_{e}, the speed of light c, the electron mass m_{e}, and on the electric- to magnetic field ratio.

Strain Balanced AlGaN/GaN/AlGaN nanomembrane HEMTs

Single crystal semiconductor nanomembranes (NM) are important in various applications such as heterogeneous integration and flexible devices. This paper reports the fabrication of AlGaN/GaN NMs and NM high electron mobility transistors (HEMT). Electrochemical etching is used to slice off single-crystalline AlGaN/GaN layers while preserving their microstructural quality. A double heterostructure design with a symmetric strain profile is employed to ensure minimal residual strain in freestanding NMs after release. The mobility of the two-dimensional electron gas (2DEG), formed by the AlGaN/GaN heterostructure, is noticeably superior to previously reported values of many other NMs. AlGaN/GaN nanomembrane HEMTs are fabricated on SiO2 and flexible polymeric substrates. Excellent electrical characteristics, including a high ON/OFF ratio and transconductance, suggest that III-Nitrides nanomembranes are capable of supporting high performance applications.

21pAC-7 大面積塗布有機単結晶の電界誘起電子スピン共鳴測定

21pAC-7 大面積塗布有機単結晶の電界誘起電子スピン共鳴測定

Scanning Kelvin Probe Microscopy Reveals Planar Defects Are Sources of Electronic Disorder in Organic Semiconductor Crystals

Electronic disorder in organic semiconductor single crystals, manifested as parallel surface potential domains with potential variations ranging from tens to hundreds of mV, is observed by scanning Kelvin probe microscopy. Chemical etching and X‐ray diffraction indicate that the potential domains are correlated with planar defects such as stacking faults. The results have important implications for understanding structure–transport relationships in organic semiconductor single crystals.

Origin of discrepancies in the experimental values of the barrier height at metal–semiconductor junctions

A possible explanation is suggested for discrepancies between experimental values obtained by different authors for the barrier height at the same metal–semiconductor junction. It is supposed that the problem is caused primarily by the structural inhomogeneity of the metal. As a result, the junction behaves as an assembly of a large number of subjunctions connected in parallel. To determine the effect of metal inhomogeneity on the properties of a junction, the dependence of the barrier height in a Schottky diode on the junction area is investigated under the assumption that, with an increase in the area of a junction between a singlecrystal semiconductor and a polycrystalline metal, the degree of inhomogeneity and, thus, the number of subjunctions, increases.

Hall Effect in Bulk-Doped Organic Single Crystals.

The standard technique to separately and simultaneously determine the carrier concentration per unit volume (N, cm-3 ) and the mobility (μ) of doped inorganic single crystals is to measure the Hall effect. However, this technique has not been reported for bulk-doped organic single crystals. Here, the Hall effect in bulk-doped single-crystal organic semiconductors is measured. A key feature of this work is the ultraslow co-deposition technique, which reaches as low as 10-9 nm s-1 and enables us to dope homoepitaxial organic single crystals with acceptors at extremely low concentrations of 1 ppm. Both the hole concentration per unit volume (N, cm-3 ) and the Hall mobility (μH ) of bulk-doped rubrene single crystals, which have a band-like nature, are systematically observed. It is found that these rubrene single crystals have (i) a high ionization rate and (ii) scattering effects because of lattice disturbances, which are peculiar to this organic single crystal.

Spontaneously formed high-performance charge-transport layers of organic single-crystal semiconductors on precisely synthesized insulating polymers

Charge-transporting semiconductor layers with high carrier mobility and low trap-density, desired for high-performance organic transistors, are spontaneously formed as a result of thermodynamic phase separation from a blend of π-conjugated small molecules and precisely synthesized insulating polymers dissolved in an aromatic solvent. A crystal film grows continuously to the size of centimeters, with the critical conditions of temperature, concentrations, and atmosphere. It turns out that the molecular weight of the insulating polymers plays an essential role in stable film growth and interfacial homogeneity at the phase separation boundary. Fabricating the transistor devices directly at the semiconductor-insulator boundaries, we demonstrate that the mixture of 3,11-didecyldinaphtho[2,3-d:2′,3′-d′]benzo[1,2-b:4,5-b′]dithiophene and poly(methyl methacrylate) with the optimized weight-average molecular weight shows excellent device performances. The spontaneous phase separation with a one-step fabrication process leads to a high mobility up to 10 cm2 V−1 s−1 and a low subthreshold swing of 0.25 V dec−1 even without any surface treatment such as self-assembled monolayer modifications on oxide gate insulators.

Interface-Mediated Self-Assembly in Inkjet Printing of Single-Crystal Organic Semiconductor Films

Recent reports have demonstrated that printing processes are more suitable for producing high-performance organic thin-film transistors (OTFTs) than vacuum processes, although the formation mechanism of solution-based films is not yet understood. Here, we use molecular dynamics simulations to show that prototypical solution-processable organic semiconductors (OSCs) form a temporal lyotropic liquid-crystalline (LLC) molecular layer at the air–liquid interface of the semiconductor solution, which subsequently serves as a versatile precursor to the growth of a single-crystalline film. The molecules exhibit spontaneous alignments of the molecular long axes to form a molecular layer that is parallel to the air–liquid interface, whereas alignment with the short axes is not observed and the molecules move diffusively within the layer. The onset of short-axis orientational and positional ordering was observed in the later stage of film growth. Our findings provide evidence that unique way of film growth occurs vi...

Single Crystal Flexible Electronics Enabled by 3D Spalling.

Flexible and stretchable electronics are becoming increasingly important in many emerging applications. Due to the outstanding electrical properties of single crystal semiconductors, there is great interest in releasing single crystal thin films and fabricating flexible electronics with these conventionally rigid materials. In this study the authors report a universal single crystal layer release process, called "3D spalling," extending beyond prior art. In contrast to the conventional way of removing blanket layers from their substrates, the new process reported here enables 3D control over the shape and thickness of the removed regions, allowing direct formation of arbitrarily shaped structures of released film and locally specified thickness for each region. As an exemplary demonstration, silicon flexible tactile sensors are fabricated with sensitivities comparable to those of high performance sensors on rigid substrates. Finite element modeling indicates that the size and thickness of the selectively released features can be tuned over a wide range.

Excitonic quasimolecules in nanosystems of quantum dots

The theory of excitonic quasimolecules (biexcitons) (formed of spatially separated electrons and holes) in a nanosystem that consists of semiconductor quantum dots synthesized in a borosilicate glass matrix is presented. It is shown that exciton quasimolecule formation is of a threshold character and is possible in nanosystem, if the spacing between the quantum dots surfaces is larger than a certain critical spacing. It was found that the binding energy of the singlet ground state of an exciton quasimolecule, consisting of two semiconductor quantum dots is a significant large values, larger than the binding energy of the biexciton in a semiconductor single crystal by almost two orders of magnitude.

Получение высокочистых гранулированных металлов: кадмия, цинка, свинца

Cadmium, zinc and lead are constituent components of many semiconductor compounds. The obtained high purity distillates and ingots are large-size elements, which is not always convenient to use, and thus require additional grinding, which does not always allow maintaining the purity of the original materials. For the growth of semiconductor and scintillation single crystals it is advisable to use «friable» granular high-purity distillates, which can be processed without the risk of contamination. For example, the European low-background experiment LUCIFER required more than 20 kg of high-purity granulated zinc, which was agreed to be supplied by NSC KIPT. This task was then extended to cadmium and lead. Motivated by these tasks, the authors of this paper propose complex processes of deep refining of cadmium, zinc and lead by vacuum distillation. A device producing granules has been developed. The process of granulation of high-purity metals is explored. The purity of produced granules for cadmium and zinc is >99,9999, and >99,9995% for lead granules. To prevent oxidation of metal granules during exposition to air, chemical methods of surface passivation were used. Organic solvent based on dimethylformamide used as a coolant improves the resistance of granules to atmospheric corrosion during the granulation of high purity Cd, Zn and Pb.

Photo-switchable field-effect transistors based on two-dimensional stilbene oligomer crystals

Large-size two-dimensional photochromic semiconductor single crystals of stilbene oligomers are prepared for application in photo-switchable organic field-effect transistors.

Spray printing of organic semiconducting single crystals.

Single-crystal semiconductors have been at the forefront of scientific interest for more than 70 years, serving as the backbone of electronic devices. Inorganic single crystals are typically grown from a melt using time-consuming and energy-intensive processes. Organic semiconductor single crystals, however, can be grown using solution-based methods at room temperature in air, opening up the possibility of large-scale production of inexpensive electronics targeting applications ranging from field-effect transistors and light-emitting diodes to medical X-ray detectors. Here we demonstrate a low-cost, scalable spray-printing process to fabricate high-quality organic single crystals, based on various semiconducting small molecules on virtually any substrate by combining the advantages of antisolvent crystallization and solution shearing. The crystals' size, shape and orientation are controlled by the sheer force generated by the spray droplets' impact onto the antisolvent's surface. This method demonstrates the feasibility of a spray-on single-crystal organic electronics.