Semiconductor Crystals Research Articles

Epitaxial Growth of III‐Vs on On‐Axis Si: Breaking the Symmetry for Antiphase Domains Control and Burying

AbstractThis work reports on the precise control of III‐V semiconductors’ antiphase domain formation and evolution during the epitaxial growth on an “on‐axis” Si (001) substrate with a very low but controlled miscut. Especially, it is shown how, starting from a Si surface having a regular array of terraces, the crystal polarity of thin GaAs epilayers grown by molecular‐beam epitaxy is defined through the Si surface topology, leading to a quasi‐periodic 1D pattern of antiphase domains in the GaAs layer. Furthermore, this work demonstrates how this configuration breaks the symmetry between the two different III‐V phases, without any step‐flow‐induced asymmetry. Following this strategy, an early burying of antiphase domains is demonstrated in GaAs epitaxially grown on a low‐miscut Si substrate. This study generalizes previous models describing antiphase domain formation and evolution and establishes the important growth parameters for the development of high crystal quality III‐V semiconductor devices monolithically integrated on low‐miscut silicon substrates.

An Optical Technique to Produce Embedded Quantum Structures in Semiconductors.

The performance of a semiconductor quantum-electronic device ultimately depends on the quality of the semiconductor materials it is made of and on how well the device is isolated from electrostatic fluctuations caused by unavoidable surface charges and other sources of electric noise. Current technology to fabricate quantum semiconductor devices relies on surface gates which impose strong limitations on the maximum distance from the surface where the confining electrostatic potentials can be engineered. Surface gates also introduce strain fields which cause imperfections in the semiconductor crystal structure. Another way to create confining electrostatic potentials inside semiconductors is by means of light and photosensitive dopants. Light can be structured in the form of perfectly parallel sheets of high and low intensity which can penetrate deep into a semiconductor and, importantly, light does not deteriorate the quality of the semiconductor crystal. In this work, we employ these important properties of structured light to form metastable states of photo-sensitive impurities inside a GaAs/AlGaAs quantum well structure in order to create persistent periodic electrostatic potentials at large predetermined distances from the sample surface. The amplitude of the light-induced potential is controlled by gradually increasing the light fluence at the sample surface and simultaneously measuring the amplitude of Weiss commensurability oscillations in the magnetoresistivity.

Optical Properties of Magnetic Monopole Excitons

Here we consider theoretically an exciton-like dipole formed by a magnetic monopole and a magnetic antimonopole. This type of quasiparticles may be formed in a magnetic counterpart of a one dimensional semiconductor crystal. We use the familiar Lorentz driven damped harmonic oscillator model to find the eigenmodes of magnetic monopole dipoles strongly coupled to light. The proposed model allows predicting optical signatures of magnetic monopole excitons in crystals.

Reclaimed water in Taiwan: current status and future prospects

According to the Taiwan Water Resources Agency, Ministry of Economic Affairs, the average water demand shortage is 530.6 million m3 yr−1 during the period of 2011 to 2019, and the situation will worsen in the near future due to global climate change. Therefore, reclaimed water has been an important new water source in Taiwan, particularly for industrial consumers such as high-tech industries in Science Parks. In order to meet the targeted reclaimed water supply of 1.32 million m3 d−1 (CMD) in 2031, Taiwan is focusing on two major reclaimed water sources, including reclaimed water from high water-consuming industries and municipal wastewater treatment plants. This report reviews current technologies used for reclaimed water including units for pretreatment, desalting, polishing, and reclamation. Case studies in Taiwan including reclaimed water from high water-consuming industries such as thin film transistor-liquid crystal display (TFT-LCD) and semiconductor industries, as well as from municipal wastewater treatment plants are presented. The TFT-LCD company Innolux and semiconductor company Advaned Semiconductor Engineering have implemented total recycled water system to recycle and reclaim wastewater from manufacturing processes, achieving a total recycled water of 290 million m3 yr−1 with about 97% recovery and 3.5 million m3 yr−1 with 80% recovery, respectively. The Fengshan reclaimed water treatment plant produces 40,436 CMD reclaimed water from municipal wastewater for the China Steel Cooperation’s steel-making processes, at an overall operation and maintenance cost of 11.5 NT dollars m−3. Meanwhile the Yongkang plant produces 15,500 CMD of reclaimed water for semiconductor and TFT-LCD manufacturing processes at an overall operation and maintenance costs of 25.8 NT dollars m−3, which is due to low urea and boron limits requested by the user. Finally, challenges and future prospects for promoting the use of reclaimed water to meet the targeted supply in 2031 will be discussed.

Robust Thermal Neutron Detection by LiInP2 Se6 Bulk Single Crystals.

Direct neutron detection based on semiconductor crystals holds promise to transform current neutron detector technologies and further boosts their widespread applications. It is, however, long impeded by the dearth of suitable materials in the form of sizeable bulk crystals. Here, we have developed high-quality centimeter-sized LiInP2 Se6 single crystals using the Bridgman method and systematically investigated their structure and property characteristics. The prototype detectors fabricated from the crystals demonstrate an energy resolution of 53.7% in response to α-particles generated from an 241 Am source and robust, well-defined response spectra to thermal neutrons that exhibit no polarization or degradation effects under prolonged neutron/γ-ray irradiation. We have also identified the primary mechanisms of Se-vacancy and InLi antisite defects in the carrier trapping process. Such insights are critical for further enhancing the energy resolution of LiInP2 Se6 bulk crystals towards the intrinsic level (∼8.6% as indicated by our chemical vapor transport-grown thin crystals). These results pave the way for practically adopting LiInP2 Se6 single crystals in new-generation solid-state neutron detectors. This article is protected by copyright. All rights reserved.

Formation of emission in diode lasers with evaporation of various impurities on the main semiconductor crystal having affinity to electron

The introduction contains a summary of modern provisions that make it impossible to interpret many phenomena occurring in diode laser systems on the basis of commonly accepted physical conceptions. The work demonstrates their inadequacy. The goal and tasks of studies have been formulated. Analysis of a solid and its internal structure (crystal) is provided. It is demonstrated that interaction of plane surface clusters determines the surface structure of solids, while the interaction between three-dimensional clusters determines the internal structure of solids (crystals). Each atom inside the crystal interacts with the first, second and third coordination layer. The value of conduction band energy is determined by displacement of the ionization boundary. For implementation of diode lasers, the distribution of electrons by Fermi-Dirac energies must have a sufficiently diffused maximum. N-conductivity emerges when ionization of negative ions occurs, the energy of affinity of which is located near the conduction band. Р-conductivity is determined by ionization of negative ions, the energy of affinity of which is located near the valence band. Р-n junction is mostly formed when two-atom molecules enter the band gap. In this case, some of the atoms have an affinity for an electron with the value of such affinity located is near the conduction band, while other atoms have an affinity for an electron near the valence band. Interband transition energy contains three components: 1 – Fermi level position energy; 2 – energy of external applied electrical field, and 3 – induced energy formed by positive charge in the valence band. Generation of laser emission takes place when two-atom molecules are adsorbed on the surface of the semiconductor crystal, in which atoms have an affinity to the electron for some of the atoms near the conduction band and for other atoms near the valence band. Maximum emission intensity occurs when external applied electrical voltage fully compensates the energy of affinity to the electron located near the conduction band.

Improvement of the electronic, mechanical and optical properties of cubic As-doped BN alloy for energy harvesting applications

The electronic structure, elastic and optical properties with wide energy band gap (Eg) in mixed crystal semiconductors containing As-doped BN are reported. Density functional calculations (DFT) were performed for comprehensive detection and understanding of structural, optoelectronic, and elastic properties for mixed semiconductors in the cubic phase. When applying Vegard’s law for As, BN, and mixed alloys based on BN1−xAsx, where x = 0, 0.25, 0.5, 0.75, and 1, we observed that the distortion of the lattice constants was slight to different condensations. Calculations of Eg values found that the values decreased with an increase in (x) condensation. The bulk modulus, and other elastic parameters were computed and confirmed that the alloys are mechanically stable. The calculations of dielectric Ɛ(ω), refractive index n(ω), higher absorption α(ω) peaks, and other coefficients confirm that BN1−xAsx alloys are favourable for practical photovoltaics. The results confirm that mixed semiconductors have great interest in next-generation optoelectronic devices. This work provides a route for optoelectronic applications.

Quantum dots in noninvasive imaging of oral squamous cell carcinomas: A scoping literature review.

The current scoping review's objective was to outline existing applications, recent breakthroughs, and quantum dots' applicability in imaging of oral squamous cell cancer. Quantum dots are nanometric semiconductor crystals with customizable optical characteristics and intense, stable fluorescence suited for bioimaging and labeling. We used the Preferred reporting items for systematic reviews and meta-analyses (PRISMA) recommendations for conducting our systematic search. An analysis of the properties and applications of quantum dots in noninvasive detection of oral squamous cell cancer is presented in this study, which comprehensively explores the available evidence. Following searches in the databases PubMed, Ovid SP, and Cochrane using the search terms quantum dots AND oral squamous cell cancer, 55 published publications were chosen for this review. The review identified a total of eight papers that met the criteria. In noninvasive detection of oral squamous cell carcinoma, quantum dots have the potential to offer an array of therapeutic and diagnostic applications. Furthermore, quantum dots emit near-infrared and visible light, which is advantageous in biological imaging since it reduces light dispersion and absorption of tissue. The future may see quantum dots become a popular noninvasive imaging technique for oral squamous cell cancer. The number of studies accessible is quite limited, and further research is required.

Influence of Growth-Equipment Vibrations on Convective Processes in Growing Doped Semiconductor Crystals

Influence of Growth-Equipment Vibrations on Convective Processes in Growing Doped Semiconductor Crystals

Disordered Phase-Assisted Growth of Organic Semiconductor Crystals on Self-Assembled Monolayer Templates.

Achieving high mobility and bias stability is a challenging obstacle in the advancement of organic thin-film transistors (OTFTs). To this end, the fabrication of high-quality organic semiconductor (OSC) thin films is critical for OTFTs. Self-assembled monolayers (SAMs) have been used as growth templates for high-crystalline OSC thin films. Despite significant research progress in the growth of OSC on SAMs, a detailed understanding of the growth mechanism of the OSC thin films on a SAM template is lacking, which has limited its use. In this study, the effects of the structure (thickness and molecular packing) of SAM on the nucleation and growth behavior of the OSC thin films were investigated. We found that disordered SAM molecules assisted in the surface diffusion of the OSC molecules and resulted in a small nucleation density and large grain size of the OSC thin films. Moreover, a thick SAM with disordered SAM molecules on the top was found to be beneficial for the high mobility and bias stability of the OTFTs.

Electromagnetic radiation of semiconductor crystals in crossed electric and magnetic fields

The features of generation of electromagnetic radiation by semiconductor crystals in crossed electric and magnetic fields have been analyzed. Analytical relations for calculating the power of cyclotron radiation have been given. The obtained results are of interest for the purposes of obtaining the sources of electromagnetic radiation in the terahertz frequency range.

Improving Photosensitivity and Transparency in Organic Phototransistor with Blending Insulating Polymers.

Organic phototransistors exhibit great promise for use in a wide range of technological applications due to their flexibility, low cost, and low-temperature processability. However, their low transparency due to visible light absorption has hindered their adoption in next-generation transparent electronics. For this reason, the present study sought to develop a highly sensitive organic phototransistor with greater transparency and significantly higher light sensitivity in the visible and UVA regions without deterioration in its electrical properties. An organic blended thin-film transistor (TFT) fabricated from the blend of an organic semiconductor and an insulating polymer demonstrated improved electrical properties in the dark and a higher current under light irradiation even though its transmittance was higher. The device exhibited a transmittance of 87.28% and a photosensitivity of 7049.96 in the visible light region that were 4.37% and 980 times higher than those of the single-semiconductor-based device. The carrier mobility of the device blended with the insulating polymer was improved and greatly amplified under light irradiation. It is believed that the insulating polymer facilitated the crystallization of the organic semiconductor, thus promoting the flow of photogenerated excitons and improving the photocurrent. Overall, the proposed TFT offers excellent low-temperature processability and has the potential to be employed in a range of transparent electronic applications.

Additive-Assisted Perylene Polymorphism Controlled via Secondary Bonding Interactions

The influence of molecular additives or impurities on crystal growth, morphology, and polymorphism has broad importance in various fields of material science and pharmaceutical engineering. There are numerous examples demonstrating the effect of impurities on the crystallization of pharmaceutical substances; however, systematic studies on the additives’ effect on crystallization and properties of organic semiconductors have not yet been reported. Here, we studied additive-assisted crystallization of a model aromatic hydrocarbon compound–perylene–to elaborate the crystal engineering tool for organic optoelectronics and to reveal the underlying mechanism. Anthracene, tetracene, 9,10-diphenylanthracene, and rubrene were used as representative additives. We found the optimal additive and conditions for perylene crystallization allowing us to control its polymorphic outcome. The addition of 9,10-diphenylanthracene was demonstrated to lead to a preferable crystallization of metastable β-form of perylene, whereas in the neat conditions, α-form was typically obtained as a stable one. The crystallization of perylene with 9,10-diphenylanthracene in high concentrations resulted in their stoichiometric co-crystallization. The perylene:9,10-diphenylanthracene co-crystal structure and optoelectronic properties were evaluated. The co-crystal demonstrated a photoluminescence quantum yield of 45% and hole mobility of 0.025 cm2/V s. The co-crystal structure analysis pointed on the stabilization of herringbone packing of perylene by interlayer C–H···π interactions, allowing the 9,10-diphenylanthracene layers to serve as the template for perylene β-polymorph nucleation. The results obtained could serve as the basis for crystallization control and engineering of high-performance materials in organic optoelectronics.

Millimeter-Sized Monoisotopic Cubic 10Boron Phosphide

Boron isotope-containing semiconductors with many novel physical properties have attracted extensive research interest in the areas such as device thermal management, optical components, and neutron detection. However, the existence of strong intrinsic covalent bonding leads to the high-temperature and high-pressure growth conditions of the single crystals of B-compound semiconductors, which has been a great bottleneck limiting their development. Here, high-quality monoisotopic cubic 10BP single crystals at a millimeter scale of approximately 1 mm were grown by a multistep ripening method based on the gas–liquid–solid principle for crystal growth. Structural and morphological analyses have shown that the 10BP single crystals prepared by this method possess a single cubic phase and high crystalline quality. The isotopic effect gives rise to the shift of characteristic peaks in the Raman spectrum. Besides, results obtained through reflection spectrum, photoluminescence (PL), and theoretical calculations demonstrate that 10BP is a semiconductor with an indirect band gap beyond 2 eV. All of these findings can prove that the multipart maturation method is a feasible way to synthesize high-quality 10BP single crystals, which provides a novel and competitive route for the study of isotopic c-BP and the growth of large-sized crystals.

Twisted Crystalline Organic Semiconductor Photodetectors

AbstractOptoelectronic properties of anisotropic crystals vary with direction requiring that the orientation of molecular organic semiconductor crystals is controlled in optoelectronic device active layers to achieve optimal performance. Here, a generalizable strategy to introduce periodic variations in the out‐of‐plane orientations of 5,11‐bis(triisopropylsilylethynyl)anthradithiophene (TIPS ADT) crystals is presented. TIPS ADT crystallized from the melt in the presence of 16 wt.% polyethylene (PE) forms banded spherulites of crystalline fibrils that twist in concert about the radial growth direction. These spherulites exhibit band‐dependent light absorption, photoluminescence, and Raman scattering depending on the local orientation of crystals. Mueller matrix imaging reveals strong circular extinction (CE), with TIPS ADT banded spherulites exhibiting domains of positive or negative CE signal depending on the crystal twisting sense. Furthermore, orientation‐dependent enhancement in charge injection and extraction in films of twisted TIPS ADT crystals compared to films of straight crystals is visualized in local conductive atomic force microscopy maps. This enhancement leads to 3.3‐ and 6.2‐times larger photocurrents and external quantum efficiencies, respectively, in photodetectors comprising twisted crystals than those comprising straight crystals.

Fourier Transform Infrared Reflection Anisotropy Spectroscopy of Semiconductor Crystals and Structures: Development and Application in the Mid-Infrared.

A new method of reflection anisotropy spectroscopy (RAS) with increased mid-IR efficiency owing to the use of a Fourier transform infrared (FT-IR) spectrometer has been developed. An optical setup was implemented using a photoelastic modulator (PEM) to modulate the direction of linear polarization of the probe beam originating from the Michelson interferometer. An original measurement algorithm was proposed to eliminate the influence of spectral inhomogeneity of the PEM efficiency on the obtained spectra using appropriate calibration. It was shown that to preserve the sign of the RAS signal, it is necessary to use a specialized procedure for phase correction of the interferogram registered by the FT-IR spectrometer. In the visible range, good agreement was confirmed between the obtained reflection anisotropy (RA) spectra of a semiconductor crystal and the results of independent measurements using a conventional diffraction-grating spectrometer-based setup. The RA spectrum of a III-V semiconductor heterostructure in the mid-infrared range (λ up to 8 µm) is demonstrated. Application of the developed FT-IR RAS method to layered black phosphorus has enabled characterization of anisotropic interband transitions in this graphene-like semiconductor crystal.

Design and analysis of Tbps all-optical gray code converter using photonic crystal-semiconductor optical amplifier-Mach–Zehnder interferometric structure

Future communication networks require the entire communication system to be all-optical to overcome the bandwidth constraints of electronics. All-optical devices play a vital role in supporting future networks, which demand a high speed of up to Tbps. An all-optical gray code converter operation was demonstrated numerically using a photonic crystal semiconductor optical amplifier (PhC-SOA) in a Mach–Zehnder interferometric (MZI) configuration at 1 Tbps for M-ary differential phase shift keying modulated binary and BCD inputs. The design achieved a very high extinction ratio of about 123.8 dB with a good quality factor value of about 45. The results show that PhC-SOA-based XOR and OR gates in the gray code converter design exhibits improved modulation features compared with traditional SOAs in our previous works.

Crystallization and photophysical dynamics of Tris(8-hydroxyquinoline) aluminum crystals fabricated by micro-spacing sublimation method

The crystallization and photophysical properties of organic semiconductors have a great influence on the device performance. In this work, micro-spacing sublimation method was used to regulate the crystallization and optical properties of tris(8-hydroxyquinoline) aluminum (Alq3) molecules. It is found that when Alq3 gas molecules contact with the cold substrate, Alq3 molecules aggregate to form small nuclei, and then grow into fiber structure. Micro-spacing distance supplies enough time for Alq3 molecules to assembly into ordered structure. The fibers will further grow to large crystals with the increase of deposition time. The density of trap states is significantly reduced as the crystal size increases owing to the strong π-π molecule interactions, leading to the higher luminescence efficiency. This work will be beneficial to the preparation of organic semiconductor crystals and study of their crystallization process, thus applied to the optimization of device performance.

Growth and thermal properties of InSe crystal by using the ground simulation apparatus of China space station

Indium selenide (InSe) semiconductor crystal was grown by using the ground simulation apparatus of China space station in this work. The furnace was controlled at 715 °C and the temperature gradient for crystal growth was ∼30 °C/cm. The as-grown InSe crystalizes in γ-phase with space group of R3m. The average etching pits density (EPD) is estimated to be about 104/cm2. Thermal analysis indicates a positive thermal expansion at 30–500 °C and no volatilization occurred even as high as 1000 °C. This work not only establishes a reliable process for preparing large-sized InSe single crystal but also creates a foundation for further work in outer space in the future.

Fast electronic trapping and de-trapping by mid-gap states in CH3NH3PbCl3 single crystal

The assumed existence of mid-gap states and their roles acting as electronic traps in lead halide perovskites are under intensive discussion. Yet, knowledge about their physical characteristics remains limited due to the lack of directly accessed optical evidence. Here, we report direct access of spectroscopic responses by mid-gap states in one prototypical metal halide perovskite, CH3NH3PbCl3 single crystal. Mid-gap electronic trapping shown by sub-gap absorption and photoluminescence quenching is demonstrated. Quenching of the inter-band photoluminescence leads to instantaneous broadening in the energetic distributions of the mid-gap, making it hard to determine the energy of each individual mid-gap state. Therefore, the subsequent mid-gap luminescence following electronic de-trapping shows largely increased spectral linewidth and varied luminescence maxima energy. Time-resolved photoluminescence revealed the fast trapping and de-trapping kinetics by mid-gap states in the CH3NH3PbCl3 single crystal. By combining existing knowledge about mid-gap states in semiconductor crystals, we define a general on-lattice surface dangling bonds scenario serving as the creation of mid-gap states in the robust CH3NH3PbCl3 single crystal.