Compared with traditional silicon materials, wide-band gap semiconductors are more suitable for making high voltage, high-frequency and high-power semiconductor devices, and are considered to be the key role of material innovation in the post-Moore era. Single-crystal diamond (SCD) has superiorities of wide-band gap, extremely high thermal conductivity and high mobility, and is expected to develop high-power, high-frequency electronic devices. However, the limitation of SCD wafer size and ultra-expensive price obstructed its promotion. After a long-time exploration, heteroepitaxy technology is recognized as an effective approach to obtain high-quality and large-size SCD wafer. This review introduces the development of heteroepitaxial SCD in detail, in aspects of substrate selection, growth mechanism and quality improvement. Furthermore, the investigations of field-effect transistors and diodes based on heteroepitaxial SCD are summarized, indicating the great potential of heteroepitaxial SCD in electronic device field. Finally, the challenges of heteroepitaxial technology are pointed out, and the potential applications are anticipated.

5G communication, energy internet, new energy automobiles, quantum technology and other advanced and sophisticated fields have put forward new and higher requirements for the performance of semiconductors. The fourth generation of semiconductor diamond is known as the “ultimate semiconductor” because of its excellent physical and chemical properties. It is considered to be the most ideal material for developing the next generation of high power, high frequency, high temperature and low power loss electronic devices. However, the technical bottleneck of shallow n-type doping has hindered the development of diamond semiconductor applications to a certain extent. The research of surface terminals has provided new strategies for the development of diamond functionalization. Diamond has realized important applications such as field effect transistors, Schottky diodes, solar-blind ultraviolet detectors, electronic emission devices and near-surface color center tuning through surface terminals. The mechanism of surface terminals exerting effects is inseparable from the characteristics of their energy band structure. In this paper, the research methods of energy band structure of several common terminals are summarized, the characteristics of their energy band structures are analyzed, the mechanism of exerting effects in combination with the characteristics are introduced, finally prospected.

Quantum light sources are fundamental modules for quantum communication and optical quantum computation. The quality of quantum light sources directly determines the implementation of quantum key distribution and optical quantum computation. For example, the indivisibility of photons ensures the unconditional security of quantum communication, and the indistinguishability of photons ensures the complexity of computing schemes. Among various solid-state candidate systems, single and entangled photon sources based on solid-state semiconductor quantum dots (QDs) have shown great potential compared to their competitors. Molecular beam epitaxy (MBE) is currently the most suitable technique for growing solid-state semiconductor QDs, with advantages of ultra-high vacuum, ultra-pure materials, in-situ monitoring, and highly controllable growth parameters. To achieve quantum light sources with high efficiency, high single-photon purity, high indistinguishability, and high entanglement fidelity simultaneously, the material growth, external field tuning, surface passivation, and optical measurement techniques of QDs need to be systematically optimized and improved. This article reviews the research progress of basic materials and devices of solid-state QDs systems based on MBE growth. Subsequently, this article discusses the mechanisms of the growth of two types of QDs, the influences of various growth parameters on the quality of QDs, including background vacuum, purity of source materials, substrate temperature, growth rate, beam equivalent pressure (BEP) ratio, etc. After that, this article introduces the technical details and experimental progress of optimizing QDs device performance from the perspectives of external field tuning, surface passivation, and improved measurement technology. Finally, the progress of quantum light sources applications in fundamental scientific problems and quantum network constructions are summarized, and prospects for practical applications and future development are discussed in brief.

Ⅲ-Ⅴ compound semiconductor epitaxial single quantum dots (QDs) are a promising candidate for preparing on-demand single photon/entangled photon pairs/photon cluster states due to their atom-like discrete energy levels. They can also be directly combined with mature integrated photon technology, making them one of the most promising solid-state quantum systems for preparing high-quality solid-state quantum light sources and constructing scalable quantum networks. In this paper, the growth and modulation of high performance semiconductor QDs using molecular beam epitaxy are discussed. Firstly, the wafer-scale epitaxy of low density InAs/GaAs QD and the technique of suppressing wetting layer states and obtaining low excitonic fine structure splitting of QDs are introduced. Then, the method of tuning the emission wavelength of QDs through strain layer is introduced, as well as the electrically controlled p-i-n devices to modulate the charges of exciton states and the emission wavelengths. Finally, the recently developed droplet epitaxy growth technique is discussed, aiming to achieve excellent quantum dot light sources.

In long-term outdoor operation, both crystalline silicon solar cells and thin film solar cells are subject to potential-induced degradation (PID), decreasing the output power of photovoltaic modules. Despite numerous studies in the past, the understanding of the PID phenomenon and its solutions is still incomplete. In order to promote a deeper understanding of the PID phenomenon in solar cells and provide guidance for stability research of solar cells, the causes of PID in crystalline silicon solar cells and thin film solar cells, as well as related solutions are reviewed in this paper.

In this work, single-crystal gallium oxide (β-Ga2O3) thin films were epitaxially grown on different off-cut angled c-plane sapphire substrates by metal organic chemical vapor deposition (MOCVD), and the effect of off-cut angles on the crystal quality and surface roughness of the epitaxial films were investigated. For the β-Ga2O3 epilayer grown on the 6° off-cut angled sapphire substrate, the full width at half maximum (FWHM) of the rocking curve is reduced to be 1.10°, together with the smallest surface roughness of 7.7 nm. Consequently, the metal-semiconductor-metal structured solar-blind ultraviolet photodetectors were fabricated by lithography, development, electron beam evaporation and lift-off techniques. The photodetector has excellent performances, including photo-dark current ratio of 6.2×106, peak photoresponsivity of 87.12 A/W at 248 nm, specific detectivity of 3.5×1015 Jones, UV-visible rejection ratio of 2.36×104, and total response time of 226.2 μs.

In this article, an AlN epitaxial layer with a step bunching surface morphology was grown on 0.2° to 1.0° offcut angle c-plane sapphire substrates by metal organic chemical vapor deposition (MOCVD), and the evolution regularity of the surface morphology during high-temperature annealing (HTA) was systematically studied. The underlying physical mechanisms were further uncovered through first-principles calculations. It is revealed that as the annealing temperature gradually increase, thermal etching pits with hexagonal structure characteristics first appear on step edges, and then polygonal pits with regular edges formed on the step terraces. The main reason is that the energy of Al-N pairs decomposed from AlN surface at the step-bunching edges (10.72 eV) is smaller than that of Al-N pairs decomposed from the step terraces (12.12 eV), which leads to the phenomenon that the morphology of step edges will change firstly during HTA. In addition, because the width of the step becomes narrower with the increase of the miscut angle, the pits of the step terraces tend to merge with the pits of the step edges during the expansion process to form a V-shaped edge, resulting in step terraces with large miscut angle hardly appearing pits. This study clarifies the evolution mechanism of step-bunching morphology of AlN grown on sapphire substrates with various offcut angles during high-temperature annealing, and provides theoretical support for the preparation of high-quality AlN templates. This template can be used for AlGaN in-plane composition modulation to obtain high-efficiency deep-ultraviolet light-emitting diodes (DUV-LEDs).

As an important topological material, α-Sn (also known as grey tin) can be turned into many topological phases including topological insulator and topological semimetal by breaking its symmetry. Until now, the study on α-Sn has been mainly focused on the topological band structures by theorical calculation and angle resolved photoemission spectroscopy (ARPES), while the epitaxial growth of α-Sn and its electronic transport properties are seldom reported due to the substrate contribution. In this paper, the research progress of α-Sn is reviewed based on the recent progress made by our group, including the epitaxial growth of high quality α-Sn films by molecular beam epitaxy (MBE), the methodology of transport measurements and topological property investigation. The transport evidence of topological semimetal phase and spin-polarized topological surface state in α-Sn is demonstrated and the topological property is engineered by thickness and strain, etc. This work provides not only important evidences for further investigation on the topological property of α-Sn, but also an essential material platform for novel quantum devices based on α-Sn.

Since playing an indispensable role in both the application and mechanism of superconductivity, superconducting films are the important link between them. Pulsed laser deposition (PLD) is one of the most commonly used techniques for growing superconducting films. In this article, the research progress on superconducting films including cuprate, iron-based, nitride and titanium oxide films by PLD is reviewed, and two developed PLD methods like superconducting long-tape and large-area-film techniques for the practical application of high-Tc superconductors are introduced. Additionally, an advanced film preparation method for high-throughput combinatorial films based on genetic engineering is recently utilized for the research of high-Tc superconductivity. Further development of the novel high-throughput superconductivity research mode will be successfully employed for building high-dimensional phase diagrams, exploring more key quantitative laws and then understanding the underlying mechanism of high-Tc superconductivity.

As device sizes in the IC industry are getting smaller and surfaces become more complex, more and more requirements are proposed on coatings, and atomic layer deposition has gained widespread attention due to its unique advantages of conformality and self-limiting growth. This paper focuses on atomic layer deposition of transparent conductive films. Firstly, some of the commonly used coating methods are briefly introduced, and details of the atomic layer deposition of thin films are reviewed, including chemical adsorption followed by surface chemical reactions. Two factors influencing the self-limiting growth of atomic layer deposition, namely deposition temperature and precursor gas flow rate, are discussed. Secondly, the morphology and composition of the films prepared by atomic layer deposition are analyzed, and the advantages are strengthened, using indium oxide as a representative example. The optoelectronic properties of some common transparent conductive films prepared by different methods, such as indium oxide, tin oxide, zinc oxide and their doped films are also summarized. Thirdly, the application range of atomic layer deposition are reviewed. It is found that high quality films can be prepared on large size substrates, such as large planar and curvature substrates, with uniform film thickness, good conformality and insignificant changes in film properties. When coating on small size substrates, such as powders, trenches and micro-nano structures, the conformality of atomic layer deposition is still obtained, with uniform film thickness and high quality film. Finally, the advantages of atomic layer deposition for thin films are summarized and its unique potential is discussed.

As a wide bandgap semiconductor, silicon carbide (SiC) has great potential in the applications of high-power, high-temperature and high-frequency power electronics owing to its excellent properties such as high breakdown electric field, high thermal conductivity, high thermal and chemical stability, and radiation resistance. The prerequisite of the widespread applications of SiC devices is to obtain large-size, high-quality and low-cost single crystal SiC. The single crystal SiC prepared by top-seeded solution growth (TSSG) method has the advantages of high crystal quality, easy diameter expansion and easy p-type doping. However, the key issue of this method is its complex growth mechanism, which has not been well understood, and it is difficult for researchers to effectively improve and optimize TSSG growth equipment and methods. Numerical simulation is considered as an effective way to explore single crystal SiC growth by TSSG method. Firstly, the fundamentals of single crystal SiC grown by TSSG method and the related numerical simulations are introduced. Main factors such as Marangoni force, buoyancy force and electromagnetic force affecting single crystal SiC growth are discussed together with the optimization of the numerical models. Finally, the key directions of the future research on the TSSG of single crystal SiC are proposed.

Owing to its high mass specific capacity and low electrode potential, lithium metal is expected to become one of the most potential anode materials for the new generation of high-energy battery systems. However, the uncontrolled growth of lithium dendrites, formation of dead lithium, and volume expansion during the cycling process not only reduce the stability in the process of cell cycle, but also cause potential safety hazard, severely restrict the practical application of the lithium metal anode. 3D current collectors play important roles in mitigating/inhibiting the volume change of lithium metal anode, delaying the growth of lithium dendrite, reducing the local current density and improving the Coulomb efficiency. However, in the actual process, the performance of the primitive one is not ideal and further modification is needed. Based on surface modification (surface coating, surface doping, surface chemical treatment) and gradient design, the research progress of 3D current collector in lithium metal battery is reviewed in this paper. The influences of lithium ion on the performance of lithium metal battery are analyzed in detail. Finally, a summary and prospect are given.

In order to solve the vibration problem of periodic lattices structure in the low-frequency field, based on the local resonance mechanism, a new composite two-dimensional periodic lattices structure was designed in this paper. The band gap mechanism of the structure and the band gap characteristics of low-frequency resonance were analyzed and studied by combining the finite element method. It is found that the initiation frequency of the band gap can be greatly reduced by optimizing the structure of the coating. The position of the band gap is determined by the natural frequency of the corresponding local resonance mode. The band gap can be adjusted to the range of meeting the practical engineering application by changing the material and size parameters of the structure. The numerical simulation results are consistent with the test results. The structure can open the full band gap of 50 Hz in the low frequency range from 40 Hz to 90 Hz, and the maximum vibration attenuation reaches 36 dB. This structure provides an effective method for obtaining low frequency and ultra-low frequency band gap of periodic lattices structure, and has potential application prospects.

Semiconductor-grade monocrystalline silicon is the basic material for the integrated circuit industry and its quality determines the performance of chips. The distribution of oxygen content in Czochralski (Cz) silicon crystals has an important impact on the quality of silicon wafers. The oxygen content distribution during crystal growth can be effectively controlled by optimizing the heat shield structure of the furnace, but it is difficult to investigate the intrinsic mechanism through experiments. In this study, effect of the structure of heat shield on the distribution of oxygen content in 200 mm semiconductor-grade Cz monocrystalline silicon was investigated by ANSYS finite element analysis. Single-section and two-section heat shield structures are widely used in commercial furnace, by comparison, the distribution of temperature and flow fields, the temperature gradient at the solid-liquid interface and the radial oxygen content distribution for different stages of body growth (300, 800, 1 000 mm) were analyzed. The simulation results demonstrate that the temperature field uniformity of the single-section heat shield structure is better than that of the two-section heat shield structure, the temperature gradient at the solid-liquid interface in the former is smaller. Also, the low argon flow rate is favorale to the volatilization of SiO gas, and weakening the shear convection of the melt, leading to an inhibition of diffusion movement of oxygen from melt to crystal. Therefore, the radial oxygen content distribution at the solid-liquid interface is more uniform and the oxygen content in the crystal is lower under the condition of the single-section heat shield structure than that of the two-section heat shield structure.

By the first-principle calculation method based on density functional theory, the adsorption processes of sulfur (S) doped, selenium (Se) doped and sulfur-selenium co-doped diamond substrates with different active groups were studied. The adsorption energy, Mulliken charge distribution and chemical bond overlap number of three different substrates with different hydrocarbon groups (C, CH, CH2, CH3) in the deposition atmosphere were calculated and analyzed. The results show that the covalent bonds between the sulfur doped model and C, CH and CH2 groups, the selenium doped model and C and CH groups, the sulfur and selenium co-doped model and C, CH and CH2 are formed through charge transferring. The bonds between sulfur doped model and CH group, and between sulfur and selenium co-doped model and C group are very close to the C—C bond of the ideal diamond. The addition of sulfur and selenium can add more growth active sites on the basis of the original diamond grain homoepitaxial growth.

In this paper, nanowire core-shell AlGaN/GaN heterostructures were designed and the effects of potential barrier layer thickness, Al component, and doping concentration on the concentration of two-dimensional electron gas (2DEG) in the planar as well as nanowire heterostructures were studied. The results show that, the rise rate of 2DEG concentration in both structures slow down as the thickness of potential barrier layer increases, and when the thickness reaches 40 nm, the 2DEG concentration gradually stabilizes due to the complete emission of surface state electrons. With the increase of Al component, the polarization effect is gradually enhanced, which makes the 2DEG concentration at the heterogeneous interface of both structures gradually increase. When the doping concentration gradually increases, it can be found that potential difference at the heterogeneous interface increases, the potential well deepening and the ability strengthening for bound electron, which finally lead to the gradual increase of 2DEG concentration. The 2DEG surface density reaches its maximum value as the doping concentration increases to 2.0×1018 cm-3. Compared with the planar structure, the nanowire structure can achieve a higher Al component, and the 2DEG surface density can reach up to 5.13×1013 cm-2 under the high Al component, which is a large improvement.

Five different Cu/Zn contained complexes were prepared using amide and azoic compound as ligand. The structures of these complexes were determined by single-crystal XRD and NMR spectra. The results show that the coordination mode and valence state of the central metal would change if the synthesis conditions were changed. In addition, electrospray mass spectrometry also confirms the different valence states of copper in different compounds. In order to explore the effects of different structures on the properties of complexes, the thioether oxidation catalysis reaction was selected as the research object. The optimal catalytic reaction conditions were explored, and it was found that the Zn based complex has the best catalytic effect. The phenylmethyl sulfide could be completely converted into sulfone at 60 ℃ for 1.75 h. Also, the catalytic efficiency of Cu2+ complexes is higher than that of Cu+ complexes. Thus, a possible catalytic reaction mechanism is proposed, in which the oxidant first binds to the central metal to form a peroxide, and then oxidizes the substrate to form corresponding sulfoxide or sulfone.

A simple and scalable method for preparing CoO nanowire@C/carbon cloth (CC) composite materials is proposed in this paper, those composite materials can be used as the negative electrode of binderless lithium-ion batteries. Firstly, CoO nanowires@CC composite materials were prepared through simple hydrothermal and calcination methods, and then CoO nanowires@C/CC composite electrode materials with three-dimensional structure were obtained through glucose solution immersion and calcination. In the unique structure, carbon coated CoO nanowires uniformly disperse on carbon cloth forming a conductive carbon network. The hierarchical CoO nanowires in situ grown on the carbon cloth can effectively shorten the transfer paths of lithium ions and reduce the contact resistance. The thickness of carbon coating is about 1 nm. The carbon coating significantly inhibits the comminution of active materials during lithium ion insertion and extraction and the direct exposure of CoO to electrolyte. The results show that CoO@C/CC nanocomposites have excellent charge discharge performance and cycle stability when used as binder free negative electrode of lithium ion battery. At the current density of 1 A·cm-2, the specific capacity after 200 cycles is 863 mAh·cm-2 (capacity retention rate 75.83%). This study provides a feasible new choice for the cathode material of flexible lithium ion battery.

In this paper, the phase, morphology, leakage current, and magnetic properties of Gd2O3 doped BiFeO3 ceramics prepared by fast liquid-phase sintering method were studied. XRD results show that Gd2O3 doping promotes the formation of a bismuth-rich phase (Bi25FeO40) and reduces the cell volume. At the same time, the phase of the ceramics transforms from three sides to opposite side, and Gd2O3 doping causes the rhombohedral structure distorts and transforms into an orthorhombic structure. SEM analysis shows that Gd2O3 doping can refine the ceramic grains. The analysis of the electrical properties show that the leakage current of ceramic samples is large, but the doping of Gd2O3 can significantly reduce the leakage current. The leakage current characteristic analysis shows that the leakage current characteristic of ceramics under low electric field is ohmic conduction, and the leakage current characteristic of pure BiFeO3 ceramics under high electric field is Schottky emission mechanism, which gradually changes into space charge limited current (SCLC) mechanism with the increase of Gd2O3 doping amount. The magnetic studies show that the magnetic Gd2O3 particles introduced by doping are uniformly distributed in the grain boundaries of ceramics, which significantly improves the magnetic properties of ceramics.