Ohmic Characteristics Research Articles

Effect of Sulfurization Temperature on Properties of Cu2ZnSnS4 Thin Films and Diffusion of Ti Substrate Elements

The addition of flexible Cu2ZnSnS4 (CZTS) thin film solar cells to titanium (Ti) substrates is an attractive way to achieve the low-cost manufacturing of photovoltaics. Prior research has indicated that the appropriate diffusion of Ti elements can enhance the crystalline growth of CZTS films. However, the excessive diffusion of Ti has been shown to adversely affect the photovoltaic performance of CZTS photovoltaic devices. Therefore, it is essential to regulate the diffusion of Ti elements within CZTS thin films to optimize their photovoltaic properties. The tendency for Ti substrate elements to diffuse into CZTS films is also influenced by the activation energy associated with these Ti elements. The sulfurization temperature is posited to be a critical factor in modulating the diffusion and activation energy of Ti elements within CZTS thin films. Consequently, this research investigates the alteration of the sulfurization temperature of CZTS thin films in order to enhance the properties of these thin films and to examine the diffusion behavior of titanium elements. The results reveal that as the sulfurization temperature increases, the diffusion of Ti elements within the CZTS thin films initially increases, then decreases, and subsequently increases again. This pattern suggests that the diffusion of Ti elements is affected not only by the activation energy of the Ti elements but also by the defect hopping distance within the CZTS thin films. Notably, at a sulfurization temperature of 550 °C, the grains at the base of the CZTS thin film demonstrate an increased density, which is associated with a reduced defect hopping distance, thereby hindering the diffusion of Ti elements within the CZTS thin films. Furthermore, at this specific sulfurization temperature, the slope of the current–voltage (I–V) curve for the CZTS/Ti structure reaches its maximum, indicating optimal ohmic contact characteristics.

CURRENT OSCILLATIONS IN IMPURITY SEMICONDUCTORS WITH BOTH SIGNS OF CURRENT CARRIERS IN THE PRESENCE OF AN EXTERNAL ELECTRIC FIELD, A TEMPERATURE GRADIENT AND A WEAK MAGNETIC FIELD (μ_± H<<C)

It is theoretically shown for the first time that in an external electric and weak magnetic fields, when there is a temperature gradient, an impurity semiconductor radiates energy from itself with a certain frequency. The values of the frequency of current oscillations and the limit of change of the external electric field are found. It is shown that the resistance in the medium has only ohmic character. It is stated that in the above semiconductor, when the concentration of electrons and holes are determined from the obtained expression in theory, the injection of contacts plays a major role for the appearance of the indicated current oscillation in the circuit.

Solution process of graphene-induced ohmic contact between the metal and AlGaN/GaN for hemts application

This work demonstrates an AlGaN/GaN high electron mobility transistor (HEMT) with Cr/Graphene ohmic contacts constructed without heat treatment. The Cr/Graphene ohmic contact was fabricated using a spray-coated graphene nanoflakes solution and electron-beam-evaporated Cr. This method does not require a high-temperature annealing step in conventional Ti/Al/Ni/Au ohmic contact. It is suggested that the Cr/graphene combination acts similarly to a doped n-type semiconductor in contact with AlGaN/GaN heterostructures, enabling carrier transport to the AlGaN layer. The investigated Au/Cr/ Graphene/AlGaN/GaN HEMT device exhibits ohmic drain characteristics in the range of -4 V to 4 V of drain-source voltage with a calculated contact resistance density of 2.5 mΩcm2. Our results have important implications for the fabrication and manufacturing of AlGaN/GaN-based microelectronic and optoelectronic devices/sensors of the future.

Impact of oxygen plasma power on the performance of Ga2O3 passivated GaN ultraviolet photodetectors

The role of oxygen plasma power on the extent of surface passivation of Gallium Nitride (GaN) epitaxial layers and the photo-response of Au/Ni/GaN Schottky detectors is investigated. The surface morphology is found to be preserved in oxide passivated GaN at intermediate plasma power which significantly deteriorates at higher power. The photoluminescence spectrum shows a fall in the intensity of band edge and defects related yellow luminescence at higher power indicating the generation of non-radiative recombination centres. The chemical and electronic structures of the passivated layer investigated by x-ray photoelectron spectroscopy revealed the formation of stoichiometric Ga2O3 up to intermediate plasma power and partial decomposition of Ga2O3 along with formation of gallium sub-oxides at higher power. This leads to an enhancement in the responsivity of the photodetector after passivation at an intermediate plasma power followed by a considerable reduction at higher power. From the electrical transport measurement across the Au/Ni/GaN Schottky diode, it is observed that the diode manifests more Schottky (Ohmic) character after oxygen plasma treatment at intermediate (higher) power. The present investigations provide a clear guideline on the selection of oxygen plasma power for surface passivation on GaN, which is highly beneficial in optimizing the performance of GaN-based optoelectronic and power devices.

Schottky-contact intrinsic current blocking layer for high efficiency AlGaInP-based red mini-LEDs.

AlGaInP-based red light emitting diodes (LEDs) are considered as promising light sources in future full-color displays. At present, vertical chip configuration is still the mainstream device structure of AlGaInP-based red LEDs. However, current crowding around p-electrode severely hinders an efficient improvement. Here, we propose a Schottky-contact current blocking layer (SCBL) to enhance current spreading and to improve light extraction efficiency of AlGaInP-based red vertical miniaturized LEDs (mini-LEDs). By utilizing the Schottky contact between ITO and p-GaP, the SCBL can hinder current crowding around the p-electrode. The current is forced to inject into an active region through a p-GaP+ ohmic contact layer, avoiding light absorption by p-electrode. Through the transfer length method, the Schottky contact characteristics between the ITO and p-GaP as well as the ohmic contact characteristics between ITO and p-GaP+ are demonstrated. Benefiting from superior current spreading and improved light extraction, a mini-LED with SCBL realizes an enhancement of 31.8% in external quantum efficiency (EQE) at 20 mA in comparison with a mini-LED without SCBL.

Study on electrical conductive mechanism of mayenite derivative C12A7:C

Abstract This study explains the conductive mechanism of C12A7:C from the perspective of crystal structure. C12A7:C is a carbon derivative of C12A7 and prepared by CaCO3 and Al2O3 in sealed graphite crucible through high-temperature sintering experiments. The main component was confirmed to be C12A7:C through X-ray diffraction inversion analysis. The four-probe method revealed that it is a semiconductor with conductivity of 4,339 S/m. A conductive model of C12A7:C crystal was established to study its conductive mechanism. Through theoretical calculations of the conductive structure model, the density of states and transfer function are important factors determining the conductivity of C12A7:C crystals. Based on the analysis of these two factors, C is the key to electron transfer in the C12A7:C crystal. Further research indicates that the C–C bond is the main form of C in C12A7:C crystals. These C–C bonds satisfy the formation conditions of conjugated systems and are key to the conductivity of C12A7:C crystals. Through simulation calculations, the volt ampere characteristic curve of C12A7:C exhibits Ohmic conductor characteristics. The conductivity of C12A7:C obtained through theoretical calculation is consistent with the experimental results. In conclusion, the conductivity of C12A7:C crystal is mainly due to the C–C conjugated system formed by carbon atoms in the crystal.

Exploring the Odd–Even Effect, Current Stabilization, and Negative Differential Resistance in Carbon-Chain-Based Molecular Devices

The transport properties of molecular devices based on carbon chains are systematically investigated using a combination of non-equilibrium Green’s function (NEGF) and density functional theory (DFT) first-principle methods. In single-carbon-chain molecular devices, a distinct even–odd behavior of the current emerges, primarily influenced by the density of states (DOS) within the chain channel. Additionally, linear, monotonic currents exhibit Ohmic contact characteristics. In ladder-shaped carbon-chain molecular devices, a notable current stabilization behavior is observed, suggesting their potential utility as current stabilizers within circuits. We provide a comprehensive analysis of the transport properties of molecular devices featuring ladder-shaped carbon chains connecting benzene-ring molecules. The occurrence of negative differential resistance (NDR) in the low-bias voltage region is noted, with the possibility of manipulation by adjusting the position of the benzene-ring molecule. These findings offer a novel perspective on the potential applications of atom chains.

Electronic properties, interface contact and transport properties of strain-modulated MS2/borophosphene and MSeS/borophosphene (M = Cr, Mo, W) heterostructure: Insights from first-principles

Controlling the interface contact performance to form low-resistance ohmic contact is of great importance in designing low-power two-dimensional (2D) devices. Here, we explore a 2D semi-metal with Dirac cones, borophosphene, for different types of contact with MS2, MSeS/borophosphene (M = Cr, Mo, W) using density functional theory (DFT) and non-equilibrium Green's function (NEGF) methods. The results indicate that under no strain, different van der Waals heterojunctions (vdWHs) exhibit an n-type (p-type) Schottky contact type, with the CrS2/borophosphene vdWHs exhibiting a lower barrier height (Φn = 0.08 eV). Next, we find that the in-plane strain is more efficient than the vertical strain. Under in-plane strain modulation, the contact type will change from Schottky to Ohmic contacts as the tensile strain increases. Similarly, the contact type will change from Schottky to semiconductor as the compressive strain increases. Under the influence of vertical strain, the CrS2/borophosphene vdWHs transition into ohmic contact only when the interlayer spacing increases to above 0.4 Å. Finally, we study the ohmic contact formation and transport characteristics based on the device angle. These findings demonstrate that interface contact types can be effectively regulated by strain, which is crucial for the design and manufacturing of novel nano electronic devices composed of borophosphene based vdWHs.

The multi-variable stepwise algorithm for internal short circuit detection in a serial battery pack with inconsistent state of health

Internal short circuit of cells is one of the main causes of thermal runaway in electric vehicle battery systems. Therefore, one of the most effective ways to prevent thermal runaway is to detect and identify internal short-circuit lithium-ion batteries before thermal runaway using a battery management system. This paper investigates the detection and identification of internal short circuits in batteries by proposing a multi-variable stepwise analysis (MSA) method. The MSA method is proposed for detecting and identifying faulty batteries by combining horizontal and vertical comparison methods and aging cells' ohmic internal resistance variation characteristics. A less consistent pack containing aging cells was designed to perform internal short-circuit experiments. Based on setting the appropriate threshold and moving the window frame horizontally, comparing the deviation degree of the ohmic internal resistance of each cell in the battery pack and the average ohmic internal resistance of the normal battery, the aging battery in the battery pack can be effectively identified. State of health (SOH) is the percentage remaining of the battery's actual maximum capacity value. The deviation degree of ohmic internal resistance of aging batteries with SOH of 92% and 80% is maintained at more than 15% and 45%. For early internal shorts with an equivalent internal short-circuit resistance of 100 Ω, the internal short-circuit detection time is 3896 s. For the short circuit in the middle and later periods (<10Ω), the MSA algorithm can achieve rapid internal short-circuit detection within the 50 s window, reducing the risk of thermal runaway. The results verified that the method could effectively identify aging cells within the battery pack and detect internal short circuits for other cells, reducing false positives and effectively preventing thermal runaway.

Studies of structural, dielectric and impedance spectroscopy of Bi4Ti2.8Sn0.2O12

The polycrystalline sample Bi4Ti2.8Sn0.2O12 was synthesized using the solid-state reaction method at 850 °C. The sample was formed in a single-phase orthorhombic structure and having space group B2ab, according to the XRD study at room temperature. The dielectric behaviors of the sample have been studied for the frequency range 1 kHz-1 MHz and a wide range of temperature 25-500 °C, which provide some important properties of the synthesized sample. The Nyquist plots provide the effect of grains and grain boundaries to the total resistance and capacitance of the synthesized compound. From ac-conductivity studies, various kinds of conduction mechanisms have been examined. The J–E characteristics support the Ohmic character of the prepared sample. The ferroelectric property at room temperature at frequency 50 Hz has been studied from polarization study.

Analysis of mortar with brake lining waste by electrical impedance spectroscopy

Several researchers have been committed to developing multifunctional mortars, that is, beyond those usual purposes, such as laying masonry, coating, and sealing. These multifunctional mortars may be able to regenerate, store energy, and self-monitor, among other features. Some of these features involve the need to increase the electrical conductivity of the mortar. In this sense, a cement mortar was produced with gradual replacement of the sand with the brake lining waste, to evaluate the electrical impedance and phase angle in a frequency spectrum from 40 Hz to 100 kHz. The specimens had aluminum electrodes embedded in them to measure the properties in question, in the hardened state. This work is a complement to preliminary research that evaluated compressive strength and impedance only at a frequency of 60 Hz, in mortars with the same mix proportion. The results indicated that increasing the content of brake lining waste when replacing sand was able to reduce electrical resistance, both at low and high frequencies. This reduction was due to the increase in electrical conductivity caused by the composition of the brake lining waste, which gives the waste ohmic characteristics. In addition to improving electrical properties, the use of brake lining waste helps to reduce waste disposal in landfills, as well as reducing the consumption of natural aggregates.

Exploring the impact of different annealing conditions on physical properties of CdSeTe thin films for solar cell absorber layer applications

The perovskite and Silicon based single junction solar cells certainly showed higher efficiency but the perovskite solar cells are highly degradable and unstable in environment whereas conventional Silicon solar cells are relatively costly. The CdTe absorber based thin film solar cells have attained efficiency of greater than 22% where doping of Selenium into the CdTe absorber layer seems to improve the photovoltaic performance. The CdCl2 treatment is proven to be critical process which induces the grain growth and recrystallization in CdSeTe films. Thus herein, air and CdCl2 annealing is performed over thermally evaporated CdSeTe thin films to seek out their applicability as an effective absorber for Cd-based thin film photovoltaics. The XRD diffractograms exposed the appearance of cubic phase with (111) preferred orientation where crystallite size is increased with annealing temperature. The optical absorbance is found to be altered with temperature of annealing and Tauc’s plots exhibited that bandgap is found to be changed in the range of 1.40–1.52 eV with increasing annealing temperature. Electrical analysis divulges Ohmic character of films where electrical resistivity and conductivity are affected by nature and temperature of post-deposition annealing. The EDS patterns confirmed the deposition of CdSeTe thin films and post deposition CdCl2 activation treatment. The FESEM images demonstrated alteration in surface morphology by grain growth where the grain size of CdSeTe films is increased from 70 nm to 235 nm with CdCl2 annealing temperature. The findings confirm that annealed CdSeTe thin films showed demanding behavior for solar cell devices as prominent light harvesting absorber layers.

Local electrical characteristic of memristor structure in a high-resistance state obtained using electrostatic force microscopy: Fractal and multifractal dynamics of surface

A heterostructure BiFeO3/TiO2(Nt)Ti (BFOT) was obtained by the atomic layer deposition (ALD) method. After thermal treatment, the redistribution of Fe/Ti atoms forms an Aurivillius intermediate layered phase, and local charge capture centers are formed in the sample. Due to cationic non-stoichiometry, the BFO film exhibits p-type conductivity, while the nanotubes exhibit n-type conductivity due to oxygen vacancies. It was observed that lateral displacement of the sample can lead to ferroelectric switching, which can, in turn, affect the transition of the memristive structure from high-resistance (HRS) to low-resistance states (LRS). The hysteresis suppression tends to transition to an ohmic character and depends on the amplitude, frequency, and duration of the periodic signal. It has been found that compensation of static charge during resistive switching can affect the transport properties of the material. Fractal dimension analysis showed an acceleration of structure restructuring with increasing voltage, possibly contributing to the transition from an insulator to a metal in certain areas of the film volume. The joint analysis of piezoresponse force microscopy (PFM), electrostatic force microscopy (EFM), and fractal/multifractal dynamics showed a correlation between surface static charge and piezopotential. The new methodology described in this work can help understand the resistive switching processes in ferroelectric/semiconductor memristive structures.

Silicon Solar Cell with Tunneling Oxide on Sulfur‐Deficient Intrinsic MoS2 Thin Film

The thermolytic growth of molybdenum disulfide thin films for solar cell applications is investigated. The thin films are spin‐coated and thermally annealed, and they show a sulfur‐deficient nanosheet structure with various spectral emissions. The intrinsic thin films are used to form heterostructures in silicon solar cells. Two types of Si solar cells are fabricated using a MoS2/p‐Si heterojunction structure and MoS2/SiOx/pn‐Si tunneling structure. The former heterojunction cell does not show photovoltaic cell character. However, the later oxide tunneling cell shows a short‐circuit current of 8.23 A, an open‐circuit voltage of 0.602 V, and a conversion efficiency of 14.6%. This indicates that the sulfur defect‐induced MoS2 thin film shows an n‐type Ohmic character, but it might not form a stable interfacial charge depletion layer with p‐Si wafers in large‐scale cell fabrication.

Influence of the Mn5Ge3/Ge ohmic-contact interface on the Seebeck coefficient of the Mn5Ge3/Ge bilayer

Thermoelectricity is a well-known effect that can be used to convert heat energy into electrical energy. However, the yield of this conversion is still low compared to current photovoltaic technology. It is limited by the intrinsic properties of materials, leading to intensive materials science investigations for the design of efficient thermoelectric (TE) materials. Interface engineering was shown to be a valuable solution for improving materials’ TE properties, supporting the development of multiphase TE materials. In particular, interfaces have been suggested to promote the increase of the Seebeck coefficient of materials without significantly impacting their electrical conductivity through the so-called energy filtering effect. This work aims at determining experimentally the effect of a metal/semiconductor interface exhibiting an ohmic character on the effective Seebeck coefficient of multiphase materials, focusing on the n-type Mn5Ge3/p-type Ge interface. This interface is shown not to contribute to carrier transport, but to contribute to carrier concentration filtering due to carrier injection or recombination. The Seebeck coefficient of the bi-phase material is shown to be dependent on the direction carriers are crossing the interface. The interface effect mainly results from a modification of charge carrier concentrations in the semiconductor.

ZrTe2 Compound Dirac Semimetal Contacts for High-Performance MoS2 Transistors.

Recent investigations reveal elemental semimetal (Bi and Sb) contacts fabricated with conventional deposition processes exhibit a remarkable capacity of approaching the quantum limit in two-dimensional (2D) semiconductor contacts, implying it might be an optimal option to solve the contact issue of 2D semiconductor electronics. Here, we demonstrate novel compound Dirac semimetal ZrTe2 contacts to MoS2 constructed by a nondestructive van der Waals (vdW) transfer process, exhibiting excellent ohmic contact characteristics with a negligible Schottky barrier. The band hybridization between ZrTe2 and MoS2 was verified. The bilayer MoS2 transistor with a 250 nm channel length on a 20 nm thick hexagonal boron nitride (h-BN) exhibits an ION/IOFF current ratio over 105 and an on-state current of 259 μA μm-1. The current results reveal that 2D compound semimetals with vdW contacts can offer a diverse selection of proper semimetals with adjustable work functions for the next-generation 2D-based beyond-silicon electronics.

Photo-induced conduction behaviour of chemically synthesized copper- doped lead sulphide hexapod

A hexapod-like structure of pure and copper-doped lead sulphide was synthesized by the chemical bath deposition technique. Subsequently, the synthesized structure was analysed through XRD, FESEM, UV–Vis and FTIR spectroscopy. The UV–Vis spectra showed a band gap exceeding 5 eV, a significant variation from the previously reported values. The investigation encompassed the study of photoconductivity switching behaviour of the samples. The results showed that the exposure to UV illumination substantially increases the photo-current. Also, the Ohmic current-voltage characteristic of the pure sample gets transformed to non-linear in the case of the doped sample. This has been attributed to the formation of intermediate states in the forbidden gap as well as the formation of local junctions between host and dopant atom. The optical switching characteristics of samples were also studied and the decay has been well-fitted with second-order exponential decay. This study is a pioneer investigation of photoconductive traits of copper-doped lead sulphide hexapod-like nanostructures.

Lead-free complex double perovskite SrLiFeWO6: Structural, microstructure, electrical and optical study

In this work, synthesis (solid-state reaction) and characterizations (structural, microstructure, dielectric, conductivity, Raman & UV–vis) of a newly prepared lead-free complex perovskite SrLiFeWO6 are reported. Preliminary X-ray diffraction (XRD) analysis suggests a tetragonal phase. The scanning electron microscope (SEM) micrograph and energy dispersive x-ray analysis (EDX) spectrum show the well-grown grains and sample purity. The study of Raman active lines determines the vibrational modes of the constituent molecules in the reported compound. Dispersed dielectric plots were explained by the Maxwell-Wagner polarization effect. The modulus study reveals the presence of a non-Debye type of relaxation. Jonscher's Power Law is fitted in ac conductivity data which follows a correlated barrier hopping mechanism. The direct bandgap energy of the studied sample is found to be 1.68 eV, which may be a good range for photovoltaic applications. For NTC thermistor applications, the analyzed thermistor constant and sensitivity factor are found to be within the permissible range. The idea of ferroelectric nature is opened up by the study of polarization versus electric field. The examination of current density versus electric field reveals that the sample has an ohmic character in the low region and a space charge-limited conduction (SCLC) mechanism in the higher field region.

First-principles study of the rectifying properties of Au/SnO2 interface

Based on the first-principles calculations, we investigate the properties of Au contacts, surface structure, and band bending for Au/SnO2(101) and Au/SnO2(100) contacts under different conditions. Our results show that the Schottky barrier height (SBH) strongly depends on the interface structure. A stoichiometric Au/SnO2(101) interface forms a Schottky contact, while Au/SnO2(100) exhibits ohmic contact characteristics. When oxygen vacancy (VO) is present in the interfacial SnO2 layer, the Fermi level shifts up to the conduction band minimum, resulting in a smaller SBH. Although Au contact on SnO2(101) with VO has non-Schottky properties, it gains Schottky properties after doping with a low-valence element. In addition, the SBHs of each interface structure are different, indicating that the modulation effect of SBH mainly depends on the rearrangement of interfacial potentials caused by the different interface structures. Such a rearrangement causes corresponding changes in the energy band at the interface, resulting in different SBHs.

Study on P-AlGaAs/Al/Au Ohmic Contact Characteristics for Improving Optoelectronic Response of Infrared Light-Emitting Device.

The Al/Au alloy was investigated to improve the ohmic characteristic and light efficiency of reflective infrared light-emitting diodes (IR-LEDs). The Al/Au alloy, which was fabricated by combining 10% aluminum and 90% gold, led to considerably improved conductivity on the top layer of p-AlGaAs of the reflective IR-LEDs. In the wafer bond process required for fabricating the reflective IR-LED, the Al/Au alloy, which has filled the hole patterns in Si3N4 film, was used for improving the reflectivity of the Ag reflector and was bonded directly to the top layer of p-AlGaAs on the epitaxial wafer. Based on current-voltage measurements, it was found that the Al/Au alloyed material has a distinct ohmic characteristic pertaining to the p-AlGaAs layer compared with those of the Au/Be alloy material. Therefore, the Al/Au alloy may constitute one of the favored approaches for overcoming the insulative reflective structures of reflective IR-LEDs. For a current density of 200 mA, a lower forward voltage (1.56 V) was observed from the wafer bond IR-LED chip made with the Al/Au alloy; this voltage was remarkably lower in value than that of the conventional chip made with the Au/Be metal (2.29 V). A higher output power (182 mW) was observed from the reflective IR-LEDs made with the Al/Au alloy, thus displaying an increase of 64% compared with those made with the Au/Be alloy (111 mW).