Ideal Semiconductor Research Articles

Preparation and ultraviolet detection performance of Cu doped <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> thin films

Solar-blind UV photodetectors (SBPs) have attracted great attention because they are widely used in missile tracking, fire detection, biochemical analysis, astronomical observations, space-to-space communications, etc. At present, it is found that wide bandgap semiconductor materials such as Al<sub><i>x</i></sub>Ga<sub>1-<i>x</i></sub>N, Mg<sub>1</sub>Zn<sub>1-<i>x</i></sub>O, diamond and <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> are ideal semiconductor materials for developing high-performance SBPs. The ultra-wide band gap semiconductor material, <i>β</i>-Ga<sub>2</sub>O<sub>3</sub>, has a large band gap width of 4.9 eV, strong breakdown electric field, absorption edge located in the solar blind ultraviolet band (200–280 nm), and it also has high transmittance in the near ultraviolet and the whole visible band. Therefore, <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> is a very suitable material for making solar blind UV photodetectors. However, the p-type <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> is difficult to dope, which limits the further development of <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> devices. In this work, the <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> thin films with different Cu doping content are grown on sapphire substrates by chemical vapor deposition method, and the morphology, crystal structure and optical properties of <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> films are measured. The test results show that the surfaces of <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> films with different Cu content are relatively smooth, and the (<inline-formula><tex-math id="M2">\begin{document}$ \bar 201 $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20230971_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20230971_M2.png"/></alternatives></inline-formula>) diffraction peak positions shift toward the lower degree side with the increase of Cu content, which indicates that Cu<sup>2+</sup> replaces Ga<sup>3+</sup> and enters into the <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> lattice. The optical absorption spectrum measurement indicates that the energy gaps of samples are evidently narrowed with the increase of Cu doping concentration. Hall measurements indicate that the Cu doped <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> thin films have a p-type conductivity with a hole concentration of 7.36 × 10<sup>14</sup>, 4.83 × 10<sup>15</sup> and 1.69 × 10<sup>16 </sup>cm<sup>–3</sup>, respectively. In addition, a photoconductive UV detector with metal-semiconductor-metal structure is prepared by evaporating Au on a Cu-doped <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> thin film, and its UV detection performance is studied. The results show that the photocurrent value of the device increases with Cu content increasing. The photo-to-dark current ratio (<i>I</i><sub>l</sub>/<i>I</i><sub>d</sub>) is about 3.8×10<sup>2</sup> of 2.4% Cu content device under 254 nm-wavelength light at 10 V. The rise time and decay time are 0.11 s and 0.13 s, respectively. Furthermore, the responsivity and external quantum efficiency can reach 1.72 A/W and 841% under 254 nm-wavelength light with a light intensity of 64 μW/cm<sup>2</sup>.

Enhanced photocatalytic activity by regulating charge transferring: Unveiling the decisive role of cerium oxide crystal-facet engineering over heterojunction

Heterojunctions have been verified to be effective for separation of photogenerated electrons and holes, therefore improving the photocatalytic efficiency. Meanwhile, cerium oxide (CeO2) is an ideal semiconductor for studying the influence of different exposed crystal facets on regulation of electron transport pathways over heterojunctions. Herein, various kinds of crystal facet-dependent CeO2/g-C3N4 (graphitic carbon nitride) heterojunctions have been successfully engineered as representative model catalysts, and their critical role in regulating charge transfer pathways has been confirmed by systemic characterizations. It was found that facet-dependent heterojunctions followed different charge transport pathways, leading to different H2 evolution activities. In detail, heterojunctions with (100) and (110) exposed surfaces followed the Z-scheme transport pathways, while heterojunction with (111) exposed surface followed the type-II pathway. The H2 evolution rates via these three kinds of heterojunctions were determined to be 3.084, 1.925, and 1.128 mmol·g−1·h−1, respectively, which were 13.3, 7.9, 4.2 times that of bare g-C3N4. It’s revealed that the different exposed crystal facets of CeO2 with different Fermi levels determine the transport pathways of photogenerated carriers. This work shows an example of controlling photocatalytic activity by facet-dependent heterojunctions and reveals the importance role of crystal-facet engineering toward heterojunction construction, which is expected to provide an important guidance for the design of new photocatalytic systems.

Variation of magnetism in a two-dimensional non-van der Waals MnS2 bilayer

Variation of magnetic properties in two-dimensional (2D) thin films are extremely important for spintronic and data-storage applications, which has inspired scientists to design 2D devices that mimic their functions. We have effectively changed the magnetism and charge transfer in the new phases of 2D MnS2 bilayer. The underlying mechanism of the variation for magnetism and electronic structure are systemically analyzed. We show that our 2D bilayers with long-ranged antiferromagnetic (AFM) orders and stable magnetic easy axes belong to ideal semiconductors, where all the Mn ions are in high-spin states. Our bilayer provides a new platform for designing 2D magnetic thin films, which is beneficial to the application of MnS2 materials in data-storage and spintronic devices with low energy consumption, nonvolatility, and high-speed.

2D electrene LaH2 monolayer: an ideal ferrovalley direct semiconductor with room-temperature ferromagnetic stability

In developing nonvolatile valleytronic devices, ferromagnetic (FM) ferrovalley semiconductors are critically needed due to the existence of spontaneous valley polarization. At present, however, the known real materials have various drawbacks towards practical applications, including the in-plane FM ground state, low Curie temperature (), small valley polarization, narrow energy window with clean polarized valley, and indirect bandgap. From first-principles calculations, here we predict an ideal ferrovalley semiconductor, honeycomb LaH2 monolayer (ML), whose intrinsic properties can overcome all these shortcomings. We demonstrate that LaH2 ML, having satisfied structural stability, is a FM half-semiconducting electrene () with its magnetic moments localized at the lattice interstitial sites rather than La atoms. At the same time, LaH2 ML holds the following desired attributes: a robust out-of-plane FM ground state with a high (334 K), a sizable valley polarization (166 meV), a wide energy window (137 meV) harboring clean single-valley carriers, and a direct bandgap. These results identify a much needed ideal ferrovalley semiconductor candidate, holding the promising application potential in valleytronics and spintronics devices.

Viewing SiGe Heterostructure for Qubits with Dislocation Theory

SiGe/Si/SiGe heterostructure serves as one of the ideal semiconductor material system to build large scale electron spin qubits[1]. To further push the scalability and extend the coherence times of qubits built on SiGe/Si/SiGe heterostructures, there are several factors to improve, one of that is the lattice homogeneity of strained Si. One source of lattice homogeneity break down are dislocations. Due to the difficulties of high quality SiGe bulk crystal growth [2-3], relaxed SiGe is commonly grown on Si substrates by epitaxy. Viewing the SiGe/Si/SiGe heterostructure on native Si substrate, dislocations half loops form unavoidably because of the misfit between SiGe and the Si substrate. These dislocation half loops consist of threading segments extending through the whole heterostructure (figure 1 (a) and (c)) [4]. Due to the stress caused by the strained Si quantum well layer, the threading dislocations can be driven to glide, resulting in additional misfit segments in the lower interface of strained Si layer when the critical thickness is exceeded (figure 1 (b)) [5]. The extension of these misfit segments is blocked when they meet other perpendicular dislocations (figure 1 (d)) [6]. These misfit dislocations destroy strain uniformity and cause tilt inside the Si layer, resulting in a distortion of the valley splitting and ultimately, reducing the coherence time of qubits [7-8].In this work, we present the observation of dislocations in SiGe/Si/SiGe heterostructures for qubit application by plan-view TEM (Figure 1 (right)). Here, the experimental observations agree with dislocation theory that threading dislocations (some are marked by (b)) will glide and elongate to have misfit segments (some are marked by (c)) in the interface when two requirements are fulfilled: misfit exists between epitaxial layer and substrate; critical thickness is exceeded. When the misfit dislocations meet perpendicular misfit dislocation line, they are blocked since the thickness is not enough to glide over it [6]. This is the case in figure 1 right marked by (d). Due to the misfit segment generation and blocking effects, the misfit dislocation spacing is proportional to the threading dislocation density both theoretically and experimentally. These misfit dislocations bring local strain field around them [9], which disturb the desired homogeneous strain field by misfit. Therefore, misfit dislocation generation needs to be suppressed if one wants to achieve homogeneous strain in Si thin layer in large scale.According to Matthews-Blakeslee theory, one can avoid the formation of misfit dislocations in the Si interface by controlling the strained layer within the critical thickness. The critical thickness of Si on Si0.7Ge0.3 is calculated as 8.5 nm. The Electron channeling contrast images of Si with difference thickness 10 nm and 5 nm grown on high threading dislocation relaxed Si0.7Ge0.3 buffer at 700°C by reduced pressure chemical vapor deposition in Figure 2 are collaborating with theory: obviously misfit dislocation appear in 10 nm Si on relaxed Si0.7Ge0.3 (Figure 2 (left)) and no misfit dislocation are presented in 5 nm Si on Si0.7Ge0.3 (Figure 2 (right)).Our results show that dislocation generation and movement needs to be taken into consideration to further develop SiGe heterostructure based qubits.

Resonant two-photon terahertz quantum cascade laser.

Lasers that can emit two photons from a single electron relaxation between two states of the same parity have been discussed since the early days of the laser era. However, such lasers have seen only limited success, mainly due to a lack of suitable gain medium. We propose that terahertz (THz) frequency quantum cascade lasers (QCLs) are an ideal semiconductor structure to realize such two-photon emissions. In this work, we present a THz QCL heterostructure designed to emit two resonant photons from each electronic relaxation between two same-parity states in the active region. We present coupled Maxwell-Bloch equations that describe the dynamics of such a two-photon laser and find analytical solutions for the steady-state light intensity, the steady-state energy-resolved carrier densities, and the total threshold carrier density. Due to the two-photon emission from each excited state relaxation and an increased photon-driven carrier transport rate, our simulations predict a significant enhancement of light intensity in our designed resonant two-photon THz QCL when compared to an exemplar conventional THz QCL structure.

Surface plasma treatment reduces oxygen vacancies defects states to control photogenerated carriers transportation for enhanced self-powered deep UV photoelectric characteristics

Ga2O3 is an ideal wide bandgap semiconductor for deep ultraviolet photodetectors due to the suitable band gap and excellent material stability, but the inevitable escape of oxygen ions from the lattices always leaves oxygen vacancies and leads to the persistent photoconductivity effect. Plasma treatment technology can use highly chemically active plasma to modify materials' surfaces at room temperature, which is environment-friendly and low carbon. In this work, we have prepared β-Ga2O3 films by plasma-enhanced chemical vapor deposition (PECVD) and used plasma treatment to reduce the oxygen vacancies in-situ. Whereafter, we constructed a Schottky-type photodetector to explore the effect of plasma treatment on the photoelectronic properties of β-Ga2O3 thin film. After plasma treatment, the oxygen vacancy reduces from 44.5 % to 27.3 %, and the photocurrent of β-Ga2O3 photodetector increases from 11 nA to 67 nA at 0 V. Furthermore, the decrease of oxygen vacancy also improves the photoresponse speed (<0.2 s) of the photodetector. The present study provides an efficient treatment method of oxygen vacancies by plasma technology to obtain high-performance self-powered deep-ultraviolet photodetectors.

Determining the mode characteristics of voltage regulator with capacitive load

The tasks of dynamic compensation of reactive power are solved by means of flexible AC transmission systems using power electronics devices. The object of this study is a variable voltage regulator with a capacitive load. This paper considered the problem of the efficiency of phase voltage regulation on the capacitor battery to use it as a source to compensate for reactive power. The results of the study are presented, which justify the effectiveness of the technique for obtaining a dynamic source of reactive power based on the use of a thyristor voltage regulator with a capacitive load. A comparative study of two regimes of the regulator was carried out: the phase-controlled mode of closing fully controlled semiconductor gates and the phase-controlled mode for opening single-core semiconductor gates. Analytical expressions for angular characteristics of power according to the main harmonics are derived. It is shown that under the first mode the current through the capacitor is capacitive, which makes it possible to obtain a thyristor-adjustable capacitor battery for dynamic compensation of reactive power in power supply systems. It was found that under the second mode, simultaneously with the regulation of reactive power, there is a phenomenon of consumption from the active power supply network according to the main harmonics. This means that the regulation of current through an ideal capacity using ideal phase-controlled semiconductor gates is accompanied by the consumption of the active component of the current from the power supply network. The resulting component of active power in the electrical circuit without active resistances is proposed to be called "active artificial shear power". The results have been confirmed by studies on virtual models

Prediction of protected band edge states and dielectric tunable quasiparticle and excitonic properties of monolayer MoSi2N4

The electronic structure of two-dimensional (2D) materials are inherently prone to environmental perturbations, which may pose significant challenges to their applications in electronic or optoelectronic devices. A 2D material couples with its environment through two mechanisms: local chemical coupling and nonlocal dielectric screening effects. The local chemical coupling is often difficult to predict or control experimentally. Nonlocal dielectric screening, on the other hand, can be tuned by choosing the substrates or layer thickness in a controllable manner. Therefore, a compelling 2D electronic material should offer band edge states that are robust against local chemical coupling effects. Here it is demonstrated that the recently synthesized MoSi2N4 is an ideal 2D semiconductor with robust band edge states protected from capricious environmental chemical coupling effects. Detailed many-body perturbation theory calculations are carried out to illustrate how the band edge states of MoSi2N4 are shielded from the direct chemical coupling effects, but its quasiparticle and excitonic properties can be modulated through the nonlocal dielectric screening effects. This unique property, together with the moderate band gap and the thermodynamic and mechanical stability of this material, paves the way for a range of applications of MoSi2N4 in areas including energy, 2D electronics, and optoelectronics.

Энергия относительного движения электрона и дырки в экситоне во внешнем электрическом поле в пластине GaAs

The dependence of the energy of the relative electron-hole motion in an exciton on the magnitude of applied electric field for various thicknesses of an ideal flat semiconductor plate is theoretically calculated. It is shown that the variation of the plate thickness significantly affects the dependence of the energy on the electric field. The effect should be observed in plates whose thickness exceeds the Bohr exciton radius by two orders of magnitude.

Energy of electron-hole relative motion in exciton in external electric field in thick GaAs plate

The dependence of the energy of the relative electron-hole motion in an exciton on the magnitude of applied electric field for various thicknesses of an ideal flat semiconductor plate is theoretically calculated. It is shown that the variation of the plate thickness significantly affects the dependence of the energy on the electric field. The effect should be observed in plates whose thickness exceeds the Bohr exciton radius by two orders of magnitude. Keywords: exciton, electrick field, thick plate.

Highly efficient Ag2O loaded ZnO/Al2O3 coupled catalyst and its photocatalytic application

The scientific community is interested in designing the ideal semiconductor nanomaterials and improving the potential of existing nanomaterials for the purification of the ecosystem. In this study, efforts were made to enhance the photocatalytic properties of earlier reported ZnO/Al2O3 binary system, by integrating with the Ag2O. This three-component system showed excellent photocatalytic properties in shorter times compared to the binary system. Two model pollutants utilized for analysis of the photocatalytic activity are Cibacron Red (CR) dye and Triclopyr (TC) pesticide. The effect of Ag2O integration on morphology, crystallinity, chemical state, and optical properties has been investigated by utilizing the FESEM, XRD, XPS, EDS, HRTEM, and UV-DRS techniques. The characterization results advocate that nanomaterials are well-crystalline, thermally stable, and porous. The results of the current study showed that the Ag2O@ZnO/Al2O3 sample consist of 7 wt% silver dosage, demonstrates the highest activity towards the photo-removal of both model pollutants under UV illumination. The outcome of the study emphasizes that the formation of this three-component nano-heterojunctions between Ag2O@ZnO/Al2O3 improves the charge separation efficiency and reduces the chances of recombination. The probable mechanism of photodegradation responsible for this improvement is also discussed.

Электротехнический комплекс для дистанционного обучения

The article identifies the difficulties arising from distant training of electro-engineering disciplines, in particular, when conducting laboratory work on the course of physics, electrical engineering and electronics. The advantages and prospects of technical means in education have been analyzed. The achievements of high-quality distance learning based on a computer laboratory of the educational and methodological electrical installation complex have been listed. Functioning of a computer laboratory supposes a connection between the server and the computers of the students and the teacher. One of the ways to implement distance learning using computer technologies when performing laboratory work on electrical disciplines has been presented. There has been considered an algorithm for solving graphical and computational tasks by using experimental data obtained when working with the test bench “Electrical Energy and Electronics”. There have been illustrated the diagrams of an AC rectifier diode, a parametric stabilizer of the electrical circuit voltage on the laboratory bench; the graphs of the current-voltage characteristics of an ideal semiconductor and real diodes, a Schottky diode, a silicon diode at different temperatures, a Zener diode. A diagram of the dependence of semiconductor band gap on temperature is presented. It has been inferred that the students must be IT competent before studying special subjects, in particular, physics and mathematics (specialist’s course “Ship Power plants and Automatic Equipment Operation”; Bachelor’s courses “Shipbuilding”, “Ship Power Plants”), as one of the areas of their professional activities is design and modernization of ships and marine equipment and automation, as well as the analysis of operational characteristics of power plants, which is impossible without special software and technologies. The proposed methods of conducting the laboratory work will prepare the trainees for solving the professional problems.

Exploring the Synthesis, Band Edge Insights, and Photoelectrochemical Water Splitting Properties of Lead Vanadates.

Exploring the ideal and stable semiconductor material for the efficient photoelectrochemical (PEC) overall water splitting reaction has remained a major challenge. Herein, we develop a facile hydrothermal method for the fabrication of monoclinic Pb3[VO4]2 and orthorhombic PbV2O6 thin films for the efficient and stable PEC overall water splitting applications. Detailed characterization was performed to study the crystal structure and optical, electrical, and electrochemical properties. The band edge positions of Pb3[VO4]2 and PbV2O6 are determined using spectroscopic data, revealing the conduction band edge positioned near the water reduction potential [∼0 V vs reversible hydrogen electrode (RHE)] and the valence band edge positioned well above the water oxidation potential, indicating the possible utilization of photogenerated electrons and holes for efficient water reduction and oxidation, respectively. With the optimized PbV2O6 thin films, a maximum photocurrent of 0.35 mA cm-2 was obtained at 1.23 V versus RHE and the stable production of both O2 and H2 is observed with >90% Faradaic efficiency. Importantly, this work demonstrates the possibility of utilizing lead vanadate materials for PEC water splitting applications.

Carbon-based CMOS integrated circuit technology: development status and future challenges

<p indent="0mm">Carbon nanotubes, with their unique electrical performance, quasi-one-dimensional size and stable structure, hold great prospect to be the most ideal semiconductor material in post-Moore era. Significant process has been made in carbon-based electronics. High semiconductor purity (better than 99.9999%) and high density (100~200 CNTs/μm) arrays of CNTs can be obtained on 4-inch wafer. The gate length of CNFET can be scaled down to <sc>5 nm</sc> with better performance than that of Si-FET. And the first carbon-based modern microprocessor, RV16X-NANO, has come out. This paper reviews the development of carbon nanotubes in materials, devices and integrated circuits, as well as their potential applications in some fields such as optoelectronics, sensor, display and radio frequency. Furthermore, this paper lists a series of challenges faced by carbon-based CMOS integrated circuits to realize continuous development and industrialization, and makes a further prospect for the development of carbon-based technology.

Surface Defect Engineering of CsPbBr3 Nanocrystals for High Efficient Photocatalytic CO2 Reduction

Converting CO2 into chemical fuels with sunlight is a very attractive approach to solve the greenhouse effect and fossil fuel crisis. Metal halide perovskite nanocrystals (NCs) have been identified as ideal semiconductor photocatalysts for photocatalytic CO2 reduction due to their unique properties, such as strong light absorption, low exciton binding energy, tunable bandgaps, and low cost. However, the pristine perovskite NCs suffering from inevitable defects, which lower their charge transfer efficiency and are detrimental to photocatalytic performance toward CO2 reduction. Herein, a facile approach to modify the surface defects of CsPbBr3 NC is demonstrated using tetrafluoroborate salts as defects treatment agent and loading Co2+ as a cocatalyst. As a result, the optimized Co2+ on the surface of defect‐free CsPbBr3‐BF4 shows a remarkable photocatalytic CO2 activity of 83.8 μmol g−1 h−1, which indicates that the surface modification can effectively suppress the undesired charge recombination in CsPbBr3 NC and promote its charge separation efficiency. This work provides an effective method to modify the surface defects of the CsPbBr3 NCs for high efficient photocatalytic CO2 reduction and broadens the photocatalytic applications of halide perovskites.

Room-Temperature Diffusion-Induced Extraction for Perovskite Nanocrystals with High Luminescence and Stability.

Metal halide perovskite nanocrystals (NCs) serve as a kind of ideal semiconductor for luminescence and display applications. However, the optoelectronic performance and stability of perovskite NCs are mainly subjected to current ligand strategies since these ligands exhibit a highly dynamic binding state, which complicates NC purification and storage. Herein, a method named diffusion-induced extraction is developed for crystallization (DEC) at room temperature, in which silicone oil serves as a medium to separate the solvent from perovskite precursors and diethyl ether promotes the nucleation, leading to highly emissive perovskite NCs. The formation mechanism of NCs using this approach is elucidated, and their optoelectronic properties are fully characterized. The resultant NCs ink exhibits a high photoluminescence quantum yield (PLQY) over 90% with a narrow full width at half maximum of 17nm. The DEC method strengthens the interaction between ligand and NCs via the hydrophobic silicone oil. Therefore, the NCs maintain almost 95% of their initial PLQYs after aging more than seven months in air. The findings will be of great significance for the continued advancement of high PLQY perovskite NCs through a better understanding of formation dynamics. The DEC strategy presents a major step forward for advancing the field of perovskite semiconductor nanomaterials.

REVIEW ON IDEAL SYSTEMS & TECHNOLOGY

This chapter contains an elaborate review of various ideal system models used to improve the characteristics of practical systems, anticipated breakthrough technologies of 21st century, and nanotechnology innovations & business opportunities : a review on how technology has affected society and its surroundings in a number of ways. In many societies, technology has helped to develop more advanced economies (including today's global economy) and has supported the rise of leisure class people. The concept of the ideal engine, ideal switch, ideal semiconductor devices like ideal diodes, transistors, etc. have been defined and taken as standards to improve the quality and performance of such practical devices or systems. It is found that, by keeping such a hypothetical device or systems in mind, researchers have to continuously improve the characteristics/properties of practical devices/systems to upgrade their performances. Hence, ideal properties of a device or a system can be used to upgrade or improve its properties toward reaching 100% efficiency. By comparing the properties/characteristics of a practical device/system with its ideal counterpart, one can find out the possible modifications in that device/system toward reaching the objective of achieving such an ideal device. In this chapter, we have also developed the concept of Ideal technology by creating a model and identified its important characteristics. These characteristics are grouped into four categories namely input conditions, output conditions, system conditions and environmental conditions/social expectations. These characteristics are further discussed, analyzed and compared with present technologies. Based on the discussion, it is realized that many of the characteristics of the ideal technology are achievable through discoveries and innovations in Nanotechnology. Finally, the characteristics of this ideal technology model are compared with nanotechnology developments and the possible way of realizing nanotechnology as ideal technology is discussed. Ideal System, Ideal Technology

Ferromagnetism With High Curie Temperature of Cu Doped LiMgN New Dilute Magnetic Semiconductors

New diluted magnetic semiconductors represented by Li(Zn,Mn)As with decoupled charge and spin doping have received much attention due to their potential applications for spintronics. However, their low Curie temperature seriously restricts the wide application of these spintronic devices. In this work, the electronic structures, ferromagnetic properties, formation energy, and Curie temperature of Cu doped LiMgN and the corresponding Li deficient system are calculated by using the first principles method based on density functional theory, combined with Heisenberg model in the Mean-Field Approximation. We find that the Cu doped systems have high temperature ferromagnetism, and the highest Curie temperature is up to 573K, much higher than the room temperature. Li(Mg0.875Cu0.125)N is a half metallic ferromagnet and its net magnetic moments are 2.0 μв. When Li is deficient, the half metallic ferromagnetism becomes stronger, the magnetic moments increase to 3.0 μв. The bonding and differential charge density indicate that the half metallic ferromagnetism can be mainly attributed to the strong hybridization between N 2p and doped Cu 3d orbitals. The results show that Cu doped LiMgN is a kind of ideal new dilute magnetic semiconductor that will benefit potential spintronics applications.

Lead-free hybrid perovskite N(CH3)4SnI3 with robust ferroelectricity induced by large and non-polar N(CH3)4+ molecular cation

The ferroelectricity in the hybrid perovskite CH3NH3PbI3 is under debate because it results from the polar molecular cation CH3NH3+ while the molecular orientation was reported to be random. Here we predict that a Pb-free hybrid perovskite N(CH3)4SnI3 with non-polar molecular cation N(CH3)4+ has strong ferroelectricity with a spontaneous polarization of 16.13 μC cm−2. The large polarization results from the distortion of SnI6 octahedron induced by the large N(CH3)4+ and is independent of the molecular orientation, so the ferroelectricity is robust. The ferroelectric R3m perovskite structure of N(CH3)4SnI3 can be synthesized as the ground state under a hydrostatic pressure over 3 GPa and remains stable under ambient pressure. Given the strong ferroelectricity, good stability and high visible-light absorption, N(CH3)4SnI3 may be an ideal light-absorber semiconductor for high-efficiency solar cells because its ferroelectric polarization can facilitate electron-hole separation and produce large bulk photovoltaic effect, making the design of homogeneous bulk photovoltaic devices possible.