N-type Semiconductor Characteristics Research Articles

Electronic energy levels and electrochemical properties of co-electrodeposited CdSe thin films

CdSe semiconductor thin films were grown on indium tin oxide (ITO) coated glass substrates by co-electrochemical deposition method. Deposition potential was kept at − 0.95 V vs. Ag/AgCl reference electrode for ten minutes. Deposition electrolyte includes an aqueous solution of 10 mM CdCl2, 20 mM H2SeO3 as precursors, 200 mM LiCl as complexing agent, and HCl for adjusting of pH. Deposited CdSe thin film was annealed at 500 °C for 30 min in air medium. Precursor and annealed CdSe thin films were characterized using a number of techniques, including SEM, EDX, XRD, UV–vis spectroscopy, and electrochemical impedance spectroscopy. SEM studies show that annealing alters the surface of precursor CdSe film from smooth to granular appearance. According to EDX analyses, the ratio of Cd/Se is close to 1.07 and 1.04 for the precursor and annealed CdSe thin film, respectively. XRD analysis shows that each film has polycrystalline structure. Precursor film has only cubic structure of CdSe, while annealed film has hexagonal structure of CdSe and cubic crystal phase of CdO. Optical energy band gap of the as-deposited CdSe film increases from 1.64 to 1.71 eV after annealing due to the mixture of the two phases. Refractive index against wavelength changes between 2.0 and 3.3. Calculations performed by using the data of Mott-Schottky measurements show that precursor CdSe film has 1.72 × 1016 cm−3, while annealed film is of 3.65 × 1017 cm−3 carrier concentration. The prepared films exhibit n-type semiconductor character. The study reports energy level diagrams of the produced semiconductor CdSe thin films by using the Mott-Schottky and Tauc's approximations. The carrier transport properties in the interface between active CdSe thin film and electrolyte are discussed based on an equivalent electronic circuit simulated to the Nyquist data of the CdSe/electrolyte system.

Geometrical and electronic properties of C-doped graphyne-like BN sheets

ABSTRACTIt has been previously indicated that graphyne-like BN (BNyne) sheets have distinct and interesting properties with graphyne and h-BN sheets. Herein, the geometric and electronic properties of C-doped graphyne-like BN (C-BNyne) sheets (including α-, β- and γ-) were systematically investigated by the first-principles calculations. The results reveal that C impurity is more likely to substitute the linear-B and corner-N sites due to the lower formation energy. The C atom incorporation could lead to a change in electron transfer and local bond lengths and a pronounced structural distortion was observed in α C-doped linear-B BNyne and in γ C-doped linear-B BNyne configurations. When a single C impurity atom was doped in linear-B site, it introduced donor levels near the bottom of the conduction band and thus the structures show n-type semiconductor character. As for C-doped corner-N site BNynes, electronic structure calculation showed p-type semiconductor character. Meanwhile, strong spin splitting phenomenon occurs in β C-doped linear-B BNyne and the spin splitting character originated from the impurity C atom and its first neighboring B atom. However, the other doped configurations are nonmagnetic semiconductor.

Theoretical Study of the Electronic Structure of Threading Edge Dislocations in GaN

Although silicon is the material mainly used for power devices, we are now approaching the performance limits of power devices based on silicon. Moreover, it is difficult to improve their performance due to the intrinsic physical properties of silicon. Gallium nitride (GaN), on the other hand, is attracting a lot of attention as an alternative material for future power devices. The bandgap of GaN is three times as wide as that of silicon, and GaN has some superior features, such as its high thermal conductively, large dielectric breakdown field, and high saturation velocity for the electrons. Therefore GaN is expected to become a key material in the next generation of power devices, enabling higher voltages and higher speed operation than current devices. Moreover, the use of GaN will allow miniaturization of the devices and higher temperature operation. During the crystal growth of GaN, however, a high density of threading dislocations appears due to the lattice mismatch with the sapphire (Al2O3), silicon carbide (SiC). Moreover, it has been reported that threading dislocations degrade the performance of GaN-based electronic devices fabricated even on GaN substrates. There have been some experimental studies in which screw or mixed dislocations have been reported as being the primary sources for the leakage current in GaN-based devices [1], whereas threading edge dislocations were found not to contribute to the leakage current [2]. Therefore, we need to fabricate GaN-based power devices to examine the electronic behavior at threading dislocations in GaN and to clarify the origin of the leakage current. As for theoretical studies, the electronic structure of threading dislocations in GaN is not fully understood, although Akiyama et al. reported the electronic structures of threading dislocations by determining the atomistic structures by empirical inter-atomic potential calculations [3]. The purpose of this theoretical study is to discover whether threading edge dislocations contribute to the leakage current or not. To do this, we used first principles calculations based on density functional theory (DFT) to examine the electronic structure at threading edge dislocations with Burghers vectors of 1/3[11-20]. In order to investigate the electronic states of threading edge dislocations in GaN, it was necessary to prepare an initial atomic structure for the dislocations. Our initial atomic structure, which has a supercell containing about 200 atoms, is shown in Fig. 1. Fig. 1(a) and Fig. 1(b) show this model in the [0001] and [1-210] directions, respectively. The model has a periodic boundary condition in the [0001] direction, parallel to the dislocation. The surface of the model shown Fig. 1(a) is terminated by fictitious hydrogen atoms [4] and the model is surrounded by a vacuum region. The shape of the model is like a square pillar. First, the model structure was optimized. It is known that several types of core configurations are proposed for 1/3[11-20] threading dislocations in GaN. In this study we focused on an 8-atom ring core configuration, a symmetric 4-atom ring core configuration, and 5/7-atom ring core configurations. The electronic structures for these relaxed atomic models were calculated. Structural optimization and electronic state calculations were performed using VASP (Vienna Ab-initio Simulation Package) [5], which is a first principles calculation code based on DFT. The electronic densities of states of several core configurations are shown in Fig. 2. Fig. 2(a), Fig. 2(b), Fig. 2(c) and Fig. 2(d) show the electronic densities of states for bulk wurtzite GaN, an 8-atoms ring core, a 5/7-atoms ring core, and a symmetric 4-atoms ring core, respectively. In Fig. 2, the Fermi level is shown by the black lines at 0 eV, and the bandgaps are shown by the shaded blue or green parts. It is known that undoped GaN generally has n-type semiconductor characteristics. Therefore, focusing on the blue parts above the Fermi level, the bandgap of every core configuration is similar to that of bulk GaN. In other words, no defect levels can be seen near the bottom of the conduction band. These results demonstrate that threading edge dislocations in gallium nitride do not contribute to leakage current in GaN-based devices. Moreover, we also discuss the atomic and electronic structures using larger scale systems. Acknowledgement This work was conducted as part of a project entrusted with “research and development for next generation of power devices that contributes to the realization of an energy saving society” (MEXT; Ministry of Education, Culture, Sports, Science and Technology). Figure 1

Fabrication of high crystalline SnS and SnS2 thin films, and their switching device characteristics

Representative tin sulfide compounds, tin monosulfide (SnS) and tin disulfide (SnS2) are strong candidates for future nanoelectronic devices, based on non-toxicity, low cost, unique structures and optoelectronic properties. However, it is insufficient for synthesizing of tin sulfide thin films using vapor phase deposition method which is capable of fabricating reproducible device and securing high quality films, and their device characteristics. In this study, we obtained highly crystalline SnS thin films by atomic layer deposition and obtained highly crystalline SnS2 thin films by phase transition of the SnS thin films. The SnS thin film was transformed into SnS2 thin film by annealing at 450 °C for 1 h in H2S atmosphere. This phase transition was confirmed by x-ray diffractometer and x-ray photoelectron spectroscopy, and we studied the cause of the phase transition. We then compared the film characteristics of these two tin sulfide thin films and their switching device characteristics. SnS and SnS2 thin films had optical bandgaps of 1.35 and 2.70 eV, and absorption coefficients of about 105 and 104 cm−1 in the visible region, respectively. In addition, SnS and SnS2 thin films exhibited p-type and n-type semiconductor characteristics. In the images of high resolution-transmission electron microscopy, SnS and SnS2 directly showed a highly crystalline orthorhombic and hexagonal layered structure. The field effect transistors of SnS and SnS2 thin films exhibited on–off drain current ratios of 8.8 and 2.1 × 103 and mobilities of 0.21 and 0.014 cm2 V−1 s−1, respectively. This difference in switching device characteristics mainly depends on the carrier concentration because it contributes to off-state conductance and mobility. The major carrier concentrations of the SnS and SnS2 thin films were 6.0 × 1016 and 8.7 × 1013 cm−3, respectively, in this experiment.

Photoelectrochemical impedance spectroscopy of electrodeposited hematite α-Fe2O3 thin films: effect of cycle numbers

In this work, hematite (α-Fe2O3) onto (FTO)-coated glass substrates have been prepared by electrodeposition technique using cyclic voltammetry process. Various samples of α-Fe2O3 with cycle numbers varied between 25 and 300 were prepared. XRD analysis shows that all films crystallize in a rhombohedral phase of hematite with a preferential orientation along (104) direction. The variation in intensity of the principal peaks shows that the crystallinity of thin films was influenced by the cycle numbers or thickness. Surface morphology studies by scanning electron microscopy (SEM) showed that an increase in the cycle numbers causes an increase in the grain size and homogenous of the surface. Moreover, the optical analysis reveals that the band gap energy varied between 2.1 and 1.9 eV in terms of cycle numbers increase. On the other hand, the photo-electrochemical impedance spectroscopy (PEIS) data have been modeled using an equivalent circuit approach. Finally, from Mott–Schottky plot, the flat-band potential and carrier density of α-Fe2O3 thin films have been determined. The results reveal that all the films showed n-type semiconductor character with a flat band potential and a carrier density changed with cycle numbers.

Carbonyl-Functionalized Cyclazines as Colorants and Air-Stable n-Type Semiconductors.

A series of π-extended cycl[3,3,2]azines (3) bearing additional carbonyl groups were synthesized via aldol condensations. Two strong electron acceptor molecules (4 and 5), with low-lying LUMO energy levels of -3.99 and -3.95 eV, respectively, were obtained. Organic thin-film transistors (TFTs) based on the cyanated cyclazine derivatives 5 were fabricated by vapor deposition, exhibiting extraordinarily stable n-type semiconductor character under ambient condition with the highest electron mobility of 0.06 cm2 V-1 s-1 consistently for more than 30 months.

Molybdovanadate [VMo7O26]5− cluster directed inorganic-organic hybrid: The highest coordination linkage and in situ isoniazid dimerization

A new inorganic-organic hybrid based on both the new molybdovanadate species and the isoniazid dimer, H4K2Na2(H2O)4(C12H12N4O2)(VMo7O26)2·10H2O (1), was synthesized and structurally characterized by single crystal X-ray crystallography, spectroscopic and thermogravimetric analyses. To our knowledge, compound 1 is the first example of inorganic-organic hybrid based on both polyoxometalate and isoniazid. In compound 1, twelve surface oxygen atoms of [VMo7O26]5− cluster are utilized to make coordination linkage with other components; creating the highest coordination connection in molybdovanadates subfamily. Interestingly, the in situ isoniazid dimerization reaction could occur during the synthesis process, and then the in situ generated isoniazid dimer could function as a linker to join the coordination assembly of 3D architecture. Furthermore, the semiconducting property of compound 1 was investigated by photophysical measurements, demonstrating the characteristics of n-type semiconductor.

α-Ferrous oxalate dihydrate: an Fe-based one-dimensional metal organic framework with extraordinary photocatalytic and Fenton activities

An Fe(ii)-based metal organic framework, α-ferrous oxalate dihydrate (α-FOD), with remarkable n-type semiconductor characteristics has been successfully prepared for use as a bifunctional catalyst in both photocatalysis and Fenton oxidation.

Preparation and electronic characteristics of anionic perylene bisimide films

Neutral perylene bisimides (PBI) are well-known n-type organic semiconductors, with number of challenging electronic properties in their neutral and reduced states. We report the characteristic electronic properties of PBI anionic films. We unexpectedly discovered that pristine PBI dianion film showed p-type character, while oxidized dianion film (dominant neutral state with few radical anions) showed normal n-type semiconductor character based on Seebeck effect measurements. Both kinds of films exhibit high electrical conductivity with a potential for thermoelectric applications. The mechanism of polarity reversal is proposed.

Synthesis of 2D Layered BiI3 Nanoplates, BiI3 /WSe2 van der Waals Heterostructures and Their Electronic, Optoelectronic Properties.

Two-dimensional layered materials (2DLMs) have attracted considerable recent interest as a new material platform for fundamental materials science and potential new technologies. Here we report the growth of layered metal halide materials and their optoelectronic properties. BiI3 nanoplates can be readily grown on SiO2 /Si substrates with a hexagonal geometry, with a thickness in the range of 10-120 nm and a lateral dimension of 3-10 µm. Transmission electron microscopy and electron diffraction studies demonstrate that the individual nanoplates are high quality single crystals. Micro-Raman studies show characteristic Ag band at ≈115 cm-1 with slight red-shift with decreasing thickness, and micro-photoluminescence studies show uniform emission around 690 nm with blue-shift with decreasing thickness. Electrical transport studies of individual nanoplates show n-type semiconductor characteristics with clear photoresponse. Further, the BiI3 can be readily grown on other 2DLMs (e.g., WSe2 ) to form van der Waals heterostructures. Electrical transport measurements of BiI3 /WSe2 vertical heterojunctions demonstrate p-n diode characteristics with gate-tunable rectification behavior and distinct photovoltaic effect. The synthesis of the BiI3 nanoplates can expand the library of 2DLMs and enable a wider range of van der Waals heterostructures.

Semiconductor Property and Corrosion Behavior of Passive Film Formed on Steel with Zinc Coating in 5% NaCl Solution

The initial stage of corrosion behavior and the semiconductor property of a passive film formed on steel with zinc coating were investigated in 5 wt.% NaCl solution using scanning electrochemical microscopy (SECM), electrochemical impedance spectroscopy (EIS), potential-capacitance measurement and the Mott–Schottky analysis method. The SECM test results reveal that the Faradic currents on the tip of the ultramicro electrode decreased with the extension of immersion time, suggesting that the coating was slowly degrading, and the water and ions gradually permeated into the coating. The tip current remained stable without obvious bursting and swelling, which revealed that no blister occurred inside the coating. EIS results also support the above conclusion, especially for long-term immersion. The potential-capacitance and Mott–Schottky analysis show that the water and ions gradually entered into the coating during the immersion process, while at the same time the coating showed the characteristics of n-type semiconductor. As the time elapsed, the capacitance value decreased and the thickness of the space charge layer declined. The decrease in the slope of the Mott–Schottky curves suggested the simultaneous increase of the carrier density, and the coating was degrading. SEM observation also exhibits an obvious coating degradation after immersion compared with the previous coating without immersion in solution.

Effect of annealing temperature on the structural, optical, and electrical properties of MoS2 electrodeposited onto stainless steel mesh

Molybdenum disulphide (MoS2) thin films were deposited on flexible stainless steel mesh (SSM) using an electrodeposition method. The influence of annealing treatment from 200 to 800 °C under a Nitrogen atmosphere for 30 min, on the structural, morphological, optical, and electrical properties of samples were investigated. X-ray diffraction showed that MoS2 thin film annealed at 700 °C exhibited the best crystalline quality with (002) preferential orientation. Scanning electron microscopy showed that the films were compact and grain size increased with increasing annealing temperature, from 825 nm to 1.5 µm, whereas annealing at a higher temperature (800 °C) resulted in a significant agglomeration of MoS2. According to the UV–Vis diffuse reflectivity spectra, the band gap of thin films was deduced in the range between 1.52 and 1.56 eV. Through photoluminescence measurement, it was demonstrated that among the five samples annealed at different temperatures, the 700 °C-annealed sample presents the lowest intensity with a narrow shape. Using the electrochemical impedance spectroscopy data, the interface was modeled as an equivalent circuit approach. From Mott–Schottky plots, the flat-band potential and the acceptor density for MoS2 thin films are determined. All the films showed an n-type semiconductor character with the highest carrier density of 4.8 × 1022 cm−3 and lowest flat-band potential of −0.55 V when the annealing was maintained at 700 °C. These results suggest that the MoS2 thin film electrodeposited on SSM substrate and annealed at 700 °C under N2 atmosphere is a promising strategy in the range of chalcogenide material suitable for the photoelectrochemical applications.

First-principles study on adsorption mechanism of hydrogen on tungsten trioxide surface

With the development of modern industrial technology, tungsten products prepared from normal tungsten powder cannot meet the demands of industry. The tungsten product produced from ultra-fine tungsten powder exhibits high strength, high toughness, and low metal plasticity-brittleness transition temperature, which greatly improves the performance of materials. Hence, it is necessary to carry out theoretical research on the micro adsorption dynamics during hydrogen reduction of tungsten trioxide to prepare ultra fine tungsten powder. In order to understand crystal characteristics of WO3 and WO3(001) surface characteristics, and to provide beneficial theoretical support for reaction law of hydrogen reduction on the WO3(001) surface, the mechanisms of H atom adsorption on cubic WO3 and WO3(001) surface are studied by the first-principles calculation based on the density functional theory (DFT) plane wave pseudo-potential method. The results show that theoretically calculated band gap of the cubic crystalline WO3 is 0.587 eV. There are two kinds of WO3(001) surfaces, WO-terminated (001) surface and O-terminated (001) surface. The W-O bond length and the bond angle of W-O-W structure change after the geometric optimization of the surface, and thus the surface relaxation is realized. The WO-terminated (001) surface shows n-type semiconductor characteristics while the O-terminated (001) surface shows p-type semiconductor characteristics. Four adsorption configurations of H atoms on the WO-terminated (001) surface and the O-terminated (001) surface, including H-O2c-H, H-O2 cH-O2c, H-O1c-H, and H-O1cH-O1c, are calculated. Among them, the adsorption energy of the H-O1c-H configuration is the smallest (-3.684 eV) with the shortest bond length of H-O bond (0.0968 nm), and hydrogen atoms lose the most of electrons (0.55e), which indicates that the H-O1c-H adsorption configuration is the most stable one. The band gap of the H-O1c-H configuration increases from 0.624 eV to 1.004 eV after adsorption, while the bandwidth of valence band is almost unchanged. The results about the density of states (DOS) reveal that 1s state of the H atom interacts with 2p and 2s states of the O atom. Strong isolated electron peaks are formed to be at about -8 and -20 eV. The outermost O1c atoms of O-terminated (001) surface contain an unsaturated bond, facilitating the bonding between two H atoms and one O1c atom. Thus, two H atoms and one O1c atom form chemical bonds respectively, and an H2O molecule is generated, leaving an oxygen vacancy on the surface after adsorption reaction. By combining experimental observations with simulation results, the mechanism of hydrogen reducing tungsten trioxide can be elaborated profoundly from a micro view.

Effect of manganese concentration on physical and electrochemical properties of Mn2+-doped ZnS thin films deposited onto ITO-(glass) substrates by electrodeposition technique

In this work, Mn2+-doped ZnS onto (ITO)-coated glass substrates have been prepared by electrodeposition technique. Various samples of the ZnS with different Mn contents 0, 0.5, 1, 2, and 3 at.% were prepared. XRD analysis shows that all films crystallize in a cubic phase of ZnS with a preferential orientation along (200) direction. The variation in peak positions of X-ray diffraction shows that the Manganese element is well incorporated into ZnS matrix and does not remain in the interstitial sites. Surface morphology studies by Atomic Force Microscopy showed that an increase in the concentration doping causes an increase in the grain size and the mean square roughness. Moreover, the optical analysis reveals that the band gap energy varied between 3.54 and 3.76 eV in terms of Mn content. On the other hand, the electrochemical impedance spectroscopy data have been modeled using an equivalent circuit approach. Finally, from Mott–Schottky plot, the flat-band potential and carrier density of Mn-doping ZnS thin films have been determined. The results reveal that all the films showed n-type semiconductor character with a flat band potential and a carrier density varying from −0.46 V to −0.57 V and 3.20 × 1016 cm−3 to 4.34 × 1016 cm−3, respectively.

Synthesis, electronic, and spectral properties of novel geranylated chalcone derivatives: a theoretical and experimental study.

Novel chalcone derivatives with different substituents attached to A and B-rings: hydroxyl, methoxyl, geranyl, and prenyl groups were synthesized. The obtained compounds were characterized by NMR, HRMS, UV-Vis, IR, and MS. The theoretical analysis was carried out in all the compounds using density functional theory (DFT) with the B3LYP, PBE0, and M06-2X functionals in combination with the 6-311G(d,p) Pople-type basis set. The excited state properties were calculated by time dependent density functional theory (TD-DFT) using the same methodology applied for the ground state properties. The calculated vertical absorption wavelengths (λmax) in gas phase and in ethanol as a solvent are consistent with the experimental ones, being the TD-DFT:B3LYP/6-311G(d,p) and PCM-TD-DFT:PBE0/6-311G(d,p) the best methodologies for these calculations with good approximation to the experimental values. The calculated reorganization energies indicated that, the four chalcone derivatives present an electron transfer character due to the smaller registered values. From these parameters it is proposed that these show an n-type semiconductor character. The localization of the frontier orbitals (HOMO and LUMO) shows that only the compound containing a hydroxyl group on the A-ring displays a marked delocalization favoring the charge-transfer process in this system. The HOMO-LUMO gap energies indicate that the inclusion of different donor groups in the rings does not improve the obtained values for this property. Graphical Abstract Relationship between spectroscopic and geometrical properties of chalcones were carried out using quantum-chemical calculations and compared with experimental values.

Doping Zn(2+) in CuS Nanoflowers into Chemically Homogeneous Zn0.49Cu0.50S1.01 Superlattice Crystal Structure as High-Efficiency n-Type Photoelectric Semiconductors.

Doping Zn(2+) in CuS nanoflower into chemically homogeneous superlattice crystal structure is proposed to convert p-type CuS semiconductor to an n-type CuS semiconductor for significantly enhanced photoelectric response performance. In this study, the chemically homogeneous Zn-doped CuS nanoflowers (Zn0.06Cu0.94S, Zn0.26Cu0.73S1.01, Zn0.36Cu0.62S1.02, Zn0.49Cu0.50S1.01, Zn0.58Cu0.40S1.02) are synthesized by reacting appropriate amounts of CuCl and Zn(Ac)2·2H2O with sulfur powders in ethanol solvothermal process. By tuning the Zn/Cu atomic ratios to ∼1:1, the chemically homogeneous Zn-doped CuS nanoflowers could be converted to the perfect Zn0.49Cu0.50S1.01 superlattice structure, corresponding to the periodic Cu-S-Zn atom arrangements in the entire crystal lattice, which can induce an effective built-in electric field with n-type semiconductor characteristics to significantly improve the photoelectric response performance, such as the lifetime of photogenerated charge carriers up to 6 × 10(-8)-6 × 10(-4) s with the transient photovoltage (TPV) response intensity to ∼44 mV. This study reveals that the Zn(2+) doping in CuS nanoflowers is a key factor in determining the superlattice structure, semiconductor type, and the dynamic behaviors of charge carriers.

Thiophene-S,S-dioxidized Indophenine: A Quinoid-Type Building Block with High Electron Affinity for Constructing n-Type Polymer Semiconductors with Narrow Band Gaps.

Three thiophene-S,S-dioxidized indophenine (IDTO) isomers, 3 a (E,E,E), 3 b (Z,E,E), and 3 c (Z,E,Z), were synthesized by oxidation of an indophenine compound. 3 b and 3 c could be converted into the most-stable 3 a by heating at 110 °C. An IDTO-containing conjugated polymer, PIDTOTT, was prepared using 3 a as a comonomer through a Stille coupling reaction, and it possesses a narrow band gap and low energy levels. In organic field effect transistors (OFETs), PIDTOTT exhibited unipolar n-type semiconductor characteristics with unexpectedly high electron mobility (up to 0.14 cm(2) V(-1) s(-1)), despite its rather disordered chain packing.

Cu2O Homojunction Solar Cells: F-Doped N-type Thin Film and Highly Improved Efficiency

Herein, F-doped Cu2O thin films with different F content are first synthesized on the ITO glass via a simple electrochemical deposition method. The prepared F-doped Cu2O thin films present n-type semiconductor character and show significantly high electronic and optical properties, especially for the one with preparation molar ratio of F/Cu = 1:2. This sample owns a unique net microstructure for a best absorption of visible-light and its electron concentration is more than ten times as that of pure Cu2O. Additionally, it has a lowest resistivity, which is beneficial for photogenerated charge transfer and the decrease of electron–hole pair recombination. The F-doped Cu2O films are utilized to fabricate Cu2O homojunction solar cells by consecutive electrochemical depositions. The conversion efficiency of the best homojunction solar cell with the F-doped Cu2O as n-type layer is nearly eight times as that with pure Cu2O as n-type layer. Hence, this study provides a strategy to improve the properties of Cu2O t...

All oxide semiconductor-based bidirectional vertical p-n-p selectors for 3D stackable crossbar-array electronics.

Three-dimensional (3D) stackable memory devices including nano-scaled crossbar array are central for the realization of high-density non-volatile memory electronics. However, an essential sneak path issue affecting device performance in crossbar array remains a bottleneck and a grand challenge. Therefore, a suitable bidirectional selector as a two-way switch is required to facilitate a major breakthrough in the 3D crossbar array memory devices. Here, we show the excellent selectivity of all oxide p-/n-type semiconductor-based p-n-p open-based bipolar junction transistors as selectors in crossbar memory array. We report that bidirectional nonlinear characteristics of oxide p-n-p junctions can be highly enhanced by manipulating p-/n-type oxide semiconductor characteristics. We also propose an associated Zener tunneling mechanism that explains the unique features of our p-n-p selector. Our experimental findings are further extended to confirm the profound functionality of oxide p-n-p selectors integrated with several bipolar resistive switching memory elements working as storage nodes.

Effect of H2O2 concentration on electrochemical growth and properties of vertically oriented ZnO nanorods electrodeposited from chloride solutions

In this work, ZnO nanostructures are electrodeposited on a transparent conducting glass from chloride baths. The influence of H2O2 concentration on the electrochemical characteristics has been studied using cyclic voltammetry (CV) and chronoamperometry (CA) techniques. From the analysis of the current transients on the basis of the Scharifker–Hills model, it is found that nucleation mechanism is progressive with a typical three-dimensional (3D) nucleation and growth process; independently with the concentration of H2O2. However, the nucleation rate of the ZnO changes with the increase of H2O2 concentration. The Mott–Schottky measurements demonstrate an n-type semiconductor character for all samples with a carrier density varying between 5.14×1018cm−3 and 1.47×1018cm−3. Scanning electron microscopy (SEM) observations show arrays of vertically aligned ZnO nanorods (NRs) with good homogeneity. The X-ray diffraction (XRD) patterns show that the ZnO deposited crystallises according to a hexagonal Würtzite-type structure and with the c-axis perpendicular to the electrode surface. The directional growth along (002) crystallographic plane is very important for deposits obtained at 5 and 7mM of H2O2. The high optical properties of the ZnO NRs with a low density of deep defects was checked by UV–vis transmittance analyses, the band gap energy of films varies between 3.23 and 3.31eV with transparency around 80–90%.