Electrical Band Gap Research Articles

(Invited) Highly Doped Si1-XGex Epitaxy in View of S/D Applications

Modern CMOS devices are a fertile ground for innovation, as scaling and conceptual evolutions drive regular updates in process and material specifications. Requirements are usually set by device modelling, which defines the performance objectives for a new technology. Simulations recently carried out assuming fin [1] and nanosheet [2] field effect transistor geometries have for instance highlighted limitations due to the growing importance of contact resistance in devices with reduced dimensions. To meet the objectives, source/drain (S/D) contact regions receive a specific attention and aggressive targets are set to enable higher-performing generations of devices. Within this framework, contact resistivities (rc) lower than 1E-9 W.cm2 are specified for sub 5 nm technology nodes. Reaching this objective for n and p-type S/D is a challenging task, both from the perspectives of obtaining the right materials and of reliably measuring low rc values [3]. Several material parameters are known to affect the final contact resistivity. Novel epitaxial growth schemes are considered to maximize the active doping concentration to narrow the Schottky barrier at the metal - S/D interface. Additionally, the composition of and strain relaxation in the S/D layer affect band alignment and must be considered.This contribution focuses on S/D epitaxial layers grown and in-situ doped by chemical vapor deposition, and on the properties of fabricated Ti / p-Si1-xGex contacts. For a given Ge concentration, the Ti / Si1-xGex:B contact resistivity is minimized for an optimized range of Si1-xGe1-x:B layer thickness, and increases as the layer relaxes [4]. With increasing Ge content, the rise in contact resistivity begins for lower thicknesses. Observed trends are nevertheless similar (Fig. 1). Please note that the targeted boron concentration is constant within each series of samples but differs for different Ge concentrations. The variations in resistivity and contact resistivity as seen for different series are assigned to the different boron concentrations rather than the variation in Ge concentration. Indeed, lower resistivities and contact resistivities are measured for higher active boron concentrations.The correlation between the electrical properties and layer thickness reported in figure 1 confirms that preserving strain in the Si1-xGex:B S/D material is important. However, the increase in S/D layer and contact resistivities with increasing layer thickness is not caused by the (small) increase in electrical band gap. Instead, B incorporation during epitaxial growth is affected by the initiation of layer relaxation and decreases as the material relaxes (R) as can be concluded from Fig. 2. This figure shows the boron concentration as function of depth for two partially relaxed Si1-xGex with 25% and 65% Ge, respectively. A reduction in B incorporation when the S/D material thickness exceeds the critical thickness for strain relaxation (tc) is observed for the whole range of Ge concentrations. This phenomenon is supported by density functional theory results which indicate a reduced propensity of boron to occupy substitutional lattice sites in relaxed Si1-xGex.

Electrochemical Control and Understanding of the Electronic and Optical Properties of ZnO Formed in Rechargeable Zn-Alkaline Batteries

Rechargeable alkaline batteries using zinc metal (Zn) electrodes are of significant interest for next-generation energy storage because of their high energy density, low cost, environmental friendliness, and inherent safety. Rechargeable Zn-alkaline batteries, however, have not been widely commercialized in part due to the low cyclability of Zn electrodes. At high depths of discharge, zinc oxide (ZnO) discharge product accumulates in the electrode, passivating the zinc-electrolyte interface and ultimately leading to cell failure. While the ZnO discharge product has been studied for decades, there is no general consensus on its local structure, composition, and electrochemical properties, nor on how these properties are affected by the electrode potential or cycling conditions.In this work, we used in operando analytical techniques including X-Ray diffraction (XRD), confocal Raman spectroscopy, electrochemical impedance spectroscopy (EIS), and ultraviolet-visible (UV-vis) spectroscopy to demonstrate that the discharge product is proton-doped ZnO with oxygen vacancies, and that the electrical conductivity, band gap, and color vary systematically as a function of electrode potential. To investigate local hydrogen and zinc environments within the ZnO discharge product, we performed ex situ solid-state 1H, 2H, and 67Zn magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. Solid-state 1H and 2H NMR measurements establish that hydrogen environments change as a function of potential, while solid-state 67Zn NMR spectra indicate that the local zinc environments are distorted compared to ZnO generated via conventional routes. We also performed 2D 1H-1H exchange (EXSY) NMR measurements to investigate proton mobility between defect environments and acquired 1D 1H-1H dipolar-mediated double quantum-filtered MAS NMR spectra to establish through-space molecular-level proximities between proton sites. This work provides insights into the dynamics of zinc electrodes in alkaline environments, as well as how to electrochemically control the defect structures and electronic and optical properties of ZnO in alkaline media, which are expected to aid the development of next-generation Zn alkaline batteries and electronic devices utilizing ZnO.

(Invited) Highly Doped Si1-XGex Epitaxy in View of S/D Applications

This contribution focuses on S/D epitaxial layers grown and in-situ doped by chemical vapor deposition, and on the properties of fabricated Ti/p-Si1-xGex contacts. The Ti/Si1-xGex:B contact resistivity and the Si1-xGe1-x:B layer resistivity are both minimized for an optimized range of layer thickness. Both parameters increase as the layer relaxes. Preserving strain in Si1-xGex:B S/D material is therefore important. The increase in S/D layer resistivity and contact resistivity with increasing layer thickness is, however, not caused by the (small) increase in electrical band gap induced by (partial) layer relaxation. Instead, B incorporation during epitaxial growth is affected by the initiation of layer relaxation and decreases with increasing degree of strain relaxation. This effect is observed for the whole range of Ge concentrations. The reduced B incorporation results in a lower carrier concentration near the layer surface which, in-turn, explains the increase in contact resistivity and layer resistivity.

The role of Al and Co co-doping on the band gap tuning of TiO2 thin films for applications in photovoltaic and optoelectronic devices

Titanium dioxide (TiO2) thin film samples were synthesized with the help of a thermal spray pyrolysis method. In our investigation, the effect of Al, Co co-doping on the structural, morphological, topographical, optical, and electronic properties of TiO2 thin films were investigated. The deposited films show that as-deposited samples are nanostructured and crystallite size is varied from 66 nm to 72 nm. The structural parameters are well-matched with experimental and theoretical calculations. Energy dispersive analysis of X-rays (EDAX) spectra show that all samples are in stoichiometric conditions. The surface roughness values are varying from 66 nm to 89 nm seen by atomic force microscopy (AFM) images. The Fermi energy level tuning was investigated both experimental and theoretical simulations. The study of optical properties recognized that the absorption edge of the (Al, Co)-co-doped TiO2 sample is tuned toward the low energy region compared to the pristine sample. The calculated electrical band gap energy is matched by the optical band gap energy. A combined study of the structural, morphological, topographical, optical and electronic properties of the compound suggests that Ti1-x Al0.06 CoxO2 is a suitable candidate for optoelectronic and photovoltaic applications.

Strain-modulated electrical and optical bandgaps of tetragonal WO3: An HSE06 hybrid functional calculation

The Heyd–Scuseria–Ernzerhof screened hybrid functional is used to investigate the strain-modulated band structure and optical properties of tetragonal WO3. An electronic bandgap of 1.53 eV for the ground state of unstrained WO3 is obtained, which is consistent with the experimental value. Upon in-plane strains of 1.36%, 3.18%, 3.37%, and 4.36% along the directions of lattice vectors a→ and b→, i.e., biaxial strains, as realized by growing WO3 on the (001) surface of LaAlO3, NdGaO3, La0.3Sr0.7Al0.65Ta0.35O3, and SrTiO3, the bandgap decreases down to 1.47 eV, 1.37 eV, 1.36 eV, and 1.30 eV, respectively. The largest change in band structure can induce the downshift of the optical absorption edge, with the optical bandgap decreasing from 2.65 eV to 2.28 eV. Further applying a strain along the direction of lattice vector c→, the bandgap can be additionally tuned very finely. Our research provides a promising tuning method for designing high efficient inorganic photovoltaic materials.

Electronic Properties of Nitrogen- and Boron-Doped Amorphous Carbon (a-C:N and a-C:B) Films from Palmyra Sugar

Amorphous carbon (a-C) film is a unique material that attracts the attention of scientists to be investigated. Nitrogen- and boron- doped amorphous carbon (a-C:N and a-C:B) have been deposited on ITO glass substrates by using nanospray method. Palmyra sugar is heated at temperature 250o C for 2.5 hours to obtain a-C. Boric acid (H3BO3) and amonium hidroxide (NH4OH) are used as the sources of boron doping and nitrogen doping. a-C:N and a-C:B are made by the variations of mole ratio for doping and amorphous carbon, that are 1:15 and 1:20. Then, these samples are dissolved into mixed dymethyl sulfoxide (DMSO) and aquades. The exfoliation process of samples has been done by applying ultrasonic cleaner for 2 hours and also centrifugated at 4000 rpm for 45 minutes. Electrical conductivity and band gap are measured by using four point probe and UV Vis. The results show that electrical conductivity increases but band gap decreases than pure a-C. Furthermore, the larger mole ratio of a:C-N and a-C:B also increases conductivity and decreases band gap, resulting between 5.5×10-1S/cm – 6.1×10-1 S/cm and 1.43 eV – 1.71 eV.

Graphitic carbon nitride/graphene nanoflakes hybrid system for electrochemical sensing of DNA bases in meat samples

This research presents a simple, fast and simultaneous electrochemical quantitative determination of nucleobases, for example guanine (G), adenine (A), and thymine (T) in a beef and chicken livers samples to measure the quality of food products based on hybrids of graphitic carbon nitride/Graphene nanoflakes (g-C3N4/GNF) modified electrode. Graphitic carbon nitride (g-C3N4) made of graphite-like covalent link connects nitrogen, nitride, and carbon atoms in the structural design with improved the electrical properties and low band gap semiconductor. The g-C3N4/GNF nanocomposite was synthesized by the hydrothermal treatment to form a porous g-C3N4 interconnected three dimensional (3D) network of g-C3N4 and GNF. The 3D g-C3N4/GNF/GCE was utilized for the detection of nucleic acid bases with a well resolved oxidation peak for the individual analyte. The electrocatalytic current was established to be a linear range from 0.3 × 10–7 to 6.6 × 10–6, 0.3 × 10–7 to 7.3 × 10–6, and 5.3 × 10−6 to 63.3 × 10−4 M for G, A, and T with a detection limit of 4.7, 3.5 and 55 nM, respectively. The diffusion co-efficient and the kinetic parameters were derived from the chronoamperometry technique. The proposed sensing strategy has been effectively used for the application in real sample analysis and observed that the electrode free from the surface fouling.

Defective boron carbide monolayer as a chemical sensor for dopamine drug

By implementing density functional theory method, we studied the dopamine (DA) drug adsorption onto pristine and double-vacancy defected BC3 (DV-BC3) monolayer in order to evaluate the potential application of this nanostructure as a sensing material. The sensitivity of the perfect BC3 nanosheet was negligible toward DA identification of the compound. The adsorption energy of the DA drug on the DV-BC3 surface was calculated to be −29.03 kcal/mol. The electrical band gap and the work function of DV-BC3 decreased from 1.75 and −4.49 to 0.95 eV and −3.27 eV, respectively, after the DA adsorption process. This illustrates the potential application of the DV-BC3 nanosheet as the electronic and work function type sensor, while the perfect BC3 may be only an electronic sensor. A major shift in the adsorption energy was predicted as the solvent dielectric constant increased.

Improved dielectric breakdown strength and energy storage properties in Er2O3 modified Sr0.35Bi0.35K0.25TiO3

The development of lead-free dielectric ceramics with excellent energy storage properties has received extensive research attention. Herein, Er2O3 modified Sr0.35Bi0.35K0.25TiO3 (SBKT) composite ceramic is investigated. As 2 wt.% Er2O3 is added, a certain amount of insulating second phase with fewer regions of high local electric field (numerically simulated by COMSOL) is formed, giving rise to the increase in the dielectric breakdown strength (BDS) due to the increased electrical resistivity and band gap, the decreased average grain size and the decreased leakage current density. This optimal composition exhibits many excellent energy storage properties, such as high energy storage density of 2.59 J/cm3, high recoverable energy storage density (Wrec) of 2.17 J/cm3 with high efficiency (η) of 83.9% at 245 kV/cm, superior stability of temperature (<1% variation of Wrec and η in −25 ~ 150 °C), frequency (~1.6% variation of Wrec with ~3.6% variation of η in 10 ~ 500 Hz) and cycling (almost no change of Wrec and η within 105 cycles), and high discharge energy density of 1.51 J/cm3 with high power density of 39.6 MW/cm3 at 200 kV/cm. In this work, we provide a novel strategy and understanding to design the advanced pulse energy storage ceramics.

Analysis on Band Layer Design and J-V characteristics of Zinc Oxide Based Junction Field Effect Transistor

This paper presents the band gap design and J-V characteristic curve of Zinc Oxide (ZnO) based on Junction Field Effect Transistor (JFET). The physical properties for analysis of semiconductor field effect transistor play a vital role in semiconductor measurements to obtain the high-performance devices. The main objective of this research is to design and analyse the band diagram design of semiconductor materials which are used for high performance junction field effect transistor. In this paper, the fundamental theory of semiconductors, the electrical properties analysis and bandgap design of materials for junction field effect transistor are described. Firstly, the energy bandgaps are performed based on the existing mathematical equations and the required parameters depending on the specified semiconductor material. Secondly, the J-V characteristic curves of semiconductor material are discussed in this paper. In order to achieve the current-voltage characteristic for specific junction field effect transistor, numerical values of each parameter which are included in analysis are defined and then these resultant values are predicted for the performance of junction field effect transistors. The computerized analyses have also mentioned in this paper.

Mesomorphic, electro-optic and dielectric behaviour of a semi-fluorinated chiral liquid crystalline material forming polar smectic phases

Attributed to the superior dielectric and electro-optical properties, ferroelectric liquid crystals have a wide implementation to display industries and academic communities. In this work, we attempt to study the mesomorphic, vibrational, dielectric, and electro-optical behaviour of a semi-fluorinated chiral liquid crystal. The chemical name of the compound is (2S)-octan-2-yl-3-fluoro-4’-[4-({6-[(2,2,2-trifluoroacetyl)oxy]hexyl}oxy)phenyl]-[1,1′-biphenyl]-4-carboxylate (acronym 1F6T(2F)). The compound is identified as a smectogen exhibiting antiferroelectric, ferroelectric and orthogonal paraelectric mesophases. The compound has a lateral dipole moment of 2.63 debye, electrical bandgap of 4.21 eV, and a non-vanishing first-order static hyperpolarizability. The dielectric studies underline three different types of collective relaxation processes which are readily modelled by the modified Cole-Cole relaxation model. Employing reverse current technique, the spontaneous polarization, rotational viscosity, and response time are calculated for the compound.

Bixbyite-Ta2N2O film prepared by HiPIMS and postdeposition annealing: Structure and properties

High-power impulse magnetron sputtering of a Ta target in precisely controlled Ar+O2+N2 gas mixtures was used to prepare amorphous N-rich tantalum oxynitride (Ta–O–N) films with a finely varied elemental composition. Postdeposition annealing of the films at 900°C for 5 min in vacuum led to their crystallization without any significant change in the elemental composition. The authors show that this approach allows preparation of a Ta–O–N film with a dominant Ta2N2O phase of the bixbyite structure. As far as the authors know, this phase has been neither experimentally nor theoretically reported yet. The film exhibits semiconducting properties characterized by two electrical (indirect or selection-rule forbidden) bandgaps of about 0.2 and 1.0 eV and one optical (direct and selection-rule allowed) bandgap of 2.0 eV (suitable for visible-light absorption up to 620 nm). This observation is in good agreement with the carried out ab initio calculations and the experimental data obtained by soft and hard X-ray photoelectron spectroscopy. Furthermore, the optical bandgap is appropriately positioned with respect to the redox potentials for water splitting, which makes this material an interesting candidate for this application.

Tunability of conductivity type and energy band gap of CdTe thin film in the electrodeposition technique

In this research, cadmium telluride (CdTe) thin films were fabricated using electrodeposition technique at 1400 mV cathodic potential. CdTe films were deposited on fluorine doped tin oxide (FTO) substrate of dimension 2.3 by 2.4 cm2 at varied time of deposition. X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet visible spectrophotometer (UV-vs), photoelectrochemical cell measurement (PEC), and energy dispersive X-ray spectroscopy (EDX) were used to characterize the structural, morphological, optical, electrical conductivity and elemental composition of electrodeposited films respectively. The particle average crystallite size was estimated as 11.98 nm. The energy band gap of as deposited films decreases as the period of deposition increases for both annealed and unannealed samples. Furthermore, the period of deposition was found to constitute major factor in the dominance of the constituent elements, thereby influencing the electrical conductivity and band gap properties of the films. Consequently, the conductivity of CdTe can be reasonably tuned when heat-treated and the tunability of the energy band gap can be achieved by varying the period of deposition in the electrodeposition technique. Despite the potential of electrodeposited CdTe in solar cells applications, synthesis of p-type CdTe in a stable way place a bottleneck to the utilization of CdTe as a good absorber layer in preventing front surface recombination when CdTe form a heterojunction with any window layer material.

Structures and UV resistance of Ag/SnO2 nanocomposite materials synthesized by horizontal vapor phase growth for coating applications

The structures and UV resistance of Ag/SnO2 nanocomposite materials was observed in this study for coating applications. Horizontal Vapor Phase Growth (HVPG) was used to synthesize the Ag/SnO2 nanocomposite materials. The ratio between Ag and SnO2 was fixed with stoichiometric mixtures of 0:5, 1:4, 2:3, 3:2, 4:1, and 5:0. Scanning electron microscope–energy-dispersive X-ray spectroscopy (SEM–EDX) was used to evaluate the morphology of the materials. The results were then compared with Density Functional Theory (DFT) analysis. Computational DFT analysis of the SnO2 (110) and Ag (111) cells have verified nanorods formation of the composite material. Moreover, DFT results of Ag/SnO2 confirmed the UV blocking properties from their computed electrical bandgap energies of the range from 2.72 to 4.84 eV. The highest UV absorbance of nanocomposite was observed for 1:4 Ag/SnO2 stoichiometric ratio with 8.09 A. The study shows that the ration of SnO2 over Ag increases, the absorbance increases as well.

Optical Properties of a Two-Dimensional GeTe Layer

Using the first principles calculations, we explored the optical properties of the two-dimensional α-GeTe structure. The 2D monolayer α-GeTe had an indirect band gap of 1.79 eV, and that indirect band gap was still observed in the bilayer although the band gap had decreased to 0.61 eV. We found that the optical band gap was much larger than the electrical band gap, which was due to the indirect band gap feature of the 2D α-GeTe system. In both systems, we found a very large refractive index in the visible range. Particularly, the bilayer system had a refractive index larger than 2.5 for blue light. Furthermore, the bilayer structure was found to have a larger reflectivity at ultraviolet frequencies. Consequently, we propose that the bilayer α-GeTe film can be utilized for potential optical device applications.

A few-layer InSe-based sensitivity-enhanced photothermal fiber sensor

Two-dimensional (2D) InSe has recently attracted increasing attention due to its outstanding electrical transport property, excellent photo-response, and direct band gap characteristics.

Investigation on energy bandgap states of amorphous SiZnSnO thin films

The variation in energy bandgaps of amorphous oxide semiconducting SiZnSnO (a-SZTO) has been investigated by controlling the oxygen partial pressure (Op). The systematic change in Op during deposition has been used to control the electrical characteristics and energy bandgap of a-SZTO. As Op increased, the electrical properties degraded, while the energy bandgap increased systematically. This is mainly due to the change in the oxygen vacancy inside the a-SZTO thin film by controlling Op. Changes in oxygen vacancies have been observed by using X-ray photoelectron spectroscopy (XPS) and investigated by analyzing the variation in density of states (DOS) inside the energy bandgaps. In addition, energy bandgap parameters, such as valence band level, Fermi level, and energy bandgap, were extracted by using ultraviolet photoelectron spectroscopy, Kelvin probe force microscopy, and high-resolution electron energy loss spectroscopy. As a result, it was confirmed that the difference between the conduction band minimum and the Fermi level in the energy bandgap increased systematically as Op increases. This shows good agreement with the measured results of XPS and DOS analyses.

A review on multifunctional attributes of zinc antimonate nanostructures towards energy and environmental applications

Zinc antimonate (ZnSb2O6/ZSO) has gained attention as a promising nanostructure because of its distorted Sb–O polyhedra in their structure, superior electrical conductivity and thermal stability. This review focuses on the most important properties of ZnSb2O6 and their applications till date. The review begins with representation of crystal structure, electronic structure and density of states of ZnSb2O6 and it continues with the representation of most important properties such as thermal, electrical, optical and carrier density to understand the electrical conductivity, Seebeck coefficient, thermal stability and band gap. Finally, the discussion is intended on the various applications of ZnSb2O6 to understand the key outcomes. In particular, energy harvesting and storage devices, including lithium-ion batteries (LIBs), supercapacitors (SCs), and solar cells, take part in a crucial role in day-today life owing to the likelihood of replacing conformist energy from fossil fuels. However, proposing an electrode material with efficiency and cost-effectiveness is crucial. This can prevail by implementing ZnSb2O6 as an electrode material and additionally in this review, this material is highlighted in sensing and catalytic applications in an extensive intellect. Finally, the futuristic outlooks are featured based on the latest advances and important findings. Hence, this review proposes that ZnSb2O6 nanostructures can be a crucial material for various environmental and energy-based multifunctional applications.

Effect of Cobalt Phthalocyanine on Synthesis and Physicochemical Properties of Polyaniline

AbstractOrganic transition metal complexes are successfully used in polymerization due to their catalytic activity in oxidative reactions. Here, polyaniline was synthesized with cobalt phthalocyanine as catalysts for the aniline oxidative polymerization. The conditions for obtaining polyaniline significantly affect the final product and the introduction of the component into the reaction mixture leads to a change in the physicochemical properties of the polymer. Thus, the effect of the catalyst on the polymer chain was determined using FTIR, UV‐visible spectral methods and atomic adsorption analysis. Electrical conductivity, thermal stability, electrochemical parameters (HOMO‐LUMO, band gap), surface morphology, and fluorescence emission spectra were estimated for the polymer samples obtained. The study of synthesized polymeric materials resulted that the use of cobalt phthalocyanines in the aniline oxidative polymerization process leads to better physicochemical properties, namely electrical conductivity, band gap and fluorescence quantum yield.

Thermoelectric Properties of Cu2SnSe3-SnS Composite.

Heavily doped degenerate semiconductors such as Cu2SnSe3 (CTSe) attracted attention in thermoelectric (TE) and optoelectronic fields, due to their high electrical conductivity and small band gap. The small Seebeck coefficient of undoped CTSe, however, is the major issue in achieving high TE performance (figure of merit, ZT). Here, we report that the Seebeck coefficient of CTSe can be controlled by adding SnS within a CTSe matrix. CTSe-SnS composite has not only high Seebeck coefficient in the range of 300–500 µVolt/K but thermal conductivity which is lower than that of pristine CTSe due to the scattering at the interface between the matrix and the SnS particles. A reasonable ZT of 0.18 is achieved at 570 K by adding a small amount (3 wt.%) of SnS to the CTSe matrix.