Barrier Height Measurements Research Articles

Photoelectrochemical Properties of Chemical Bath Deposited CdNiSe Thin Films

The chemical bath deposition approach was used to prepare Cd1−xNixSe thin film photoelectrodes on a substrate made of stainless-steel plate. The constructed cell has the configuration: p-CdNiSe | NaOH (1M)+S (1M)+Na2S (1M) | C (graphite). Studying current-voltage characteristics in the dark, capacitance–voltage in the dark, barrier-height measurements, power output, photo response, and spectral response are all part of characterizing the photoelectrochemical cell of the photoelectrodes. For the composition of Cd0.7Ni0.3Se, the junction ideality factor was determined to be minimal. It was discovered that the flat band potential and barrierheight was 710 mV and 0.181 eV respectively. The power output characteristic reveals that, for composition x = 0.3, the short circuit current, open circuit voltage, conversion efficiency and fill factor are respectively, 161 μA/cm2, 260 mV, 0.64% and 48.11%. The greatest current recorded at 725 nm is displayed in the spectral response.

Over 6 MV/cm operation in β-Ga2O3 Schottky barrier diodes with IrO2 and RuO2 anodes deposited by molecular beam epitaxy

β -Ga2O3 is actively touted as the next ultrawide bandgap material for power electronics. To fully utilize its high intrinsic critical electric field, development of high-quality robust large-barrier height junctions is essential. To this end, various high-work function metals, metal oxides, and hole-conducting oxides have been deposited on Ga2O3, primarily formed by sputter deposition. Unfortunately, reports to date indicate that measured barrier heights often deviate from the Schottky–Mott model as well as x-ray photoelectron spectroscopy (XPS) extractions of conduction band offsets, suggesting significant densities of electrically active defects at these junctions. We report Schottky diodes made from noble metal oxides, IrO2 and RuO2, deposited by ozone molecular beam epitaxy (ozone MBE) with barrier heights near 1.8 eV. These barriers show close agreement across extraction methods and robust to high surface electric fields upward of 6 MV/cm and 60 A/cm2 reverse current without degradation.

Analysis of barrier inhomogeneities in Ti/p–type strained Si0.95Ge0.05 Schottky diodes using reverse current-voltage characteristics

Extracting electrical parameters such as barrier height inhomogeneities (BHi) from the forward bias can be very challenging in metal/semiconductor (M/Sc) contacts characterized by low barrier height and high series resistance. In this work we demonstrate that the reverse bias characteristics can be used as an efficient alternative method to investigate the inhomogeneity of low barrier height in M/Sc contacts. In particular, the BHi in Ti/p-strained Si0.95Ge0.05 Schottky barrier diodes (SBD) has been investigated using reverse current–voltage-temperature (IR-VR-T) characteristics over the temperature range of 100–300 K. The temperature dependence of the measured barrier heights (ΦRBp) using reverse-bias is successfully explained in terms of a thermionic emission (TE) current transport associated with Gaussian distribution of the barrier height due BHi. The mean homogeneous barrier height (Ф‾RBp) and its corresponding standard deviation (σRs) were determined for different reverse voltages. A decrease in Ф‾RBp and an increase in σRs with increasing reverse bias are observed, indicating a large barrier height distribution upon high applied reverse bias. The deduced average zero-field barrier height (ФFBp≈0.59eV) from IR-VR agrees well with the corresponding value determined from the forward characteristics. Moreover, the reverse bias extracted values for Richardson constant A* based on BHi model, are found in fair agreement with the reported theoretical value of 32 A cm−2 K−2 for our p-type strained Si0.95Ge0.05 alloy. Finally, the results obtained on Pd/n-type Si0.90Ge0.10 structure shown in this work fully support the utilization of such reverse bias method.

Optimizing Photovoltaic Efficiency Through Di-Indium Tri-Selenide Thin Film Solar Cells

This study focuses on investigating the photovoltaic efficiency of chemically deposited In2Se3 thin films for solar energy conversion. Thin film solar cells have several advantages, including reduced material usage, cost-effectiveness, and the potential for improved efficiency. Our research specifically explores the viability of chemically deposited In2Se3 thin films for converting solar energy into electrical energy through chemical processes. The photovoltaic (PV) cell configuration consists of In2Se3 thin films as the photoanode and a sulfide-polysulphide (0.15 M) solution as the electrolyte. The structure of the cell is n-In2Se3 | NaOH (0.15 M)+ S (0.15 M)+Na2S (0.15 M) |C (graphite). To comprehensively analyze the performance of the thin films, we employ various characterization techniques. These include studying the current-voltage characteristics under both dark and light conditions, capacitance–voltage in the dark, barrier height measurements, power output analysis, photo response evaluation, and spectrum response examinations. Through these analyses, we have discovered that In2Se3 exhibits n-type conductivity. Noteworthy results include a junction ideality factor of 3.43, a flat band potential of −0.680 V, and a barrier height of 0.193 eV. The power output characteristics provide crucial insights into the performance of the PV cell. We measured the open circuit voltage, short circuit current, fill factor, efficiency, and photo response lighted ideality factor, which were found to be 320 mV, 25.4 μA, 36.46%, 0.69%, and 2.56, respectively. This research significantly contributes to our understanding of the photovoltaic efficiency of di-indium tri-selenide thin film solar cells. It offers valuable insights for optimizing their performance in solar energy conversion applications.

Green synthesis of carbon dot structures from Rheum Ribes and Schottky diode fabrication.

In this study, we aimed to synthesize new carbon dot structures (CDs) in a single step by using the plant Rheum Ribes for the first time and to contribute to the studies in the field of diode fabrication by using the new CDs. The CDs were obtained by hydrothermal synthesis, which is commonly used in the literature. TEM and zeta potential measurements were used to determine morphology and sizes of the CDs, and XRD, XPS, and FTIR and micro-Raman spectroscopy were used for structural characterization. Optical characterization of the CDs was done by absorption and steady-state fluorescence measurements. In the second part of the study, CDs were dripped onto silicon substrates, and a CDs thin film was formed by evaporation. A diode structure was obtained by evaporating gold with the shadow mask technique on the CDs film, and the current-voltage characteristics of this diode were examined. The synthesized CDs are spherical with an average size of 5.5 nm, have a negative surface charge and contain 73.3 atom % C, 24.0 atom % O, and 2.7 atom % N. The CDs exhibit fluorescence at approximately 394 nm. The layer thickness and bandgap energy of the prepared CDs film were calculated as 566 nm and 5.25 eV, respectively. The ideality factor and the measured barrier height (Φb) of the CDs-based Schottky diode were calculated as 9.1 and 0.364 eV, respectively. The CDs were used as semiconductor material in a Schottky diode, and the diode exhibited rectification behavior. The results obtained from this study showed that CDs can be applied in the field of electronics, apart from sensor studies, which are common application areas.

Dependence of diode behaviour and photoresponse of Ga-doped ZnO (GZO)/p-Si junction on the carrier concentration of GZO layer

Ga-doped ZnO (GZO)/p-Si junctions were fabricated by reactive co-sputtering of Zn-GaAs target in Ar–O2 atmosphere. Highly degenerate GZO (carrier concentration ∼1021 cm−3) deposited at 4 % O2 forms non-rectifying contact with p-Si. GZO/p-Si diodes fabricated with moderately doped GZO layers deposited at 5 % O2, having carrier concentration ∼1019 cm−3 display low turn-on voltage (≲ 0.5 V) and ideality factor ≈ 2. Measurement of barrier height by temperature dependent I–V and built-in potential by C–V reveal respective values of (0.74 ± 0.07 eV) and (0.44 ± 0.04 eV), suggesting formation of Schottky type diodes. These diodes display nearly linear I–V characteristics under UV illumination, yielding photoresponsivity ∼1 A/W at ± 1 V. In contrast, GZO/p-Si diodes fabricated with lightly doped (non-degenerate) GZO layers deposited at 6–8 % O2, having carrier concentration ∼1018 cm−3, show higher turn-on voltages (4.5–6.5 V) and ideality factors of 2.5–2.7. I–V and C–V measurements reveal nearly equal values of barrier height and built-in potential, indicating formation of n-p heterojunctions, with near-elimination of conduction band discontinuity. Under UV illumination, I–V characteristics of these GZO/p-Si diodes display non-linear behaviour in forward bias and yield photoresponsivity of ∼0.1 A/W at ±1 V.

Probing unfolding barriers in high throughput.

Energy barriers between protein states determine the rate at which a folded protein makes excursions to and from any high energy states. These may include functional states or potentially harmful states. Although barriers between states are important features of a protein's energy landscape, we do not understand how they are encoded in a protein's primary sequence. Therefore, we have developed an assay coupling quantitative proteolysis with a high throughput display system to probe the effect of sequence changes on a protein's unfolding barrier. Under certain conditions, proteolytic resistance arises solely from a large kinetic barrier to unfolding, allowing us to measure barrier heights directly. In addition to expanding our basic knowledge of protein folding, exploration of the relationship between sequence and kinetic barrier heights may contribute to a greater understanding of how pathogenic protein states arise and may aid to the development of long-lived, shelf-stable protein drugs.

Fabrication and characterization of Ag-BaF2/GaSb Schottky diode

The Ag-BaF2/GaSb Schottky diode measurement has been investigated by using voltage versus current (I-V) at different temperatures, voltage versus capacitance (C-V) and hotoelectric measurements on n-type GaSb carrier per cm-3, Current – voltage measurement were used to study the interface layer. Near ideal characteristics were observed for Ag-BaF2/GaSb contact with ideality factor values (1.21-1.451). The Schottky barrier height and donor concentration (Nd) have been obtained from C-V characteristics. Barrier height results from these methods were the same approximately with the results obtained from current – voltage measurement and were in the same range which suggests that the Fermi level is pinned in the lower half of the band gap. Photoelectric measurements were used for barrier height measurements by applying the fowler method. The surfaces of sample was analyses using scanning electron microscopy (SEM) and also the x-ray is used to investigate the reasons for the non-ideal behavior of Ga contacts and to study the surface of Ag-BaF2 layer on the air-cleaved n-GaSb surface.

Effect of Temperature on Photovoltaic Solar Cell Cadmium Telluride Thin Film

Solar cell technology comes with unique temperature coefficients. These temperature coefficients are important and temperature of the solar cell has direct influence on the power output of a photovoltaic cells. CdTe is a very robust and chemically stable material and for this reason its related solar cell. Thin film photovoltaic technology is now the only thin film technology in the first top 10 producers in the world. The strong improvement in efficiency in the last 7 years was obtained by a new redesign of the CdTe solar cell device reaching a single solar cell. In this paper, we describe the fabrication process following the history of the solar cell as it was developed in the early years up to the latest development and changes. The configuration of fabricated cell is n-CdTe/NaOH (0.15 M) + S (0.15 M) + Na2S (0.15 M)/C(graphite). The junction ideality factor was found to be 2.63, 2.13, and 1.89. The flat band potential is found to be -0.400, -0.450, -0.501 V. The barrier height value was found to be 0.523, 0.487, and 0.436 eV. The study of power output characteristic shows open circuit voltage, short circuit current, fill factor and efficiency were found to be 120 mV, 24.2 μA, 32.68%, 26.18%, and 19.73% and 0.63%, 0.37%, and 0.23%, respectively. The lighted ideality factor was calculated and found to be 3.26, 1.87, and 1.17. Spectra attain maximum value of current at λ = 580 nm and decrease with increase in wavelength. The photovoltaic cell characterization of the thin films is carried out by studying current-voltage characteristics in dark, capacitance-voltage in dark, barrier height measurements, power output characteristics.

Photoelectric, optical and microstructural characterization of thin palladium silicide (Pd2Si) layers fabricated by magnetron sputtering from a stoichiometric target

The properties of thin Pd2Si layers fabricated by means of magnetron sputtering deposition from a stoichiometric target was examined. Optical parameters were determined using spectroscopic ellipsometry. The refraction indexes (n) and extinction coefficients (k) of a Pd2Si layer as a function of light wavelength were obtained. The microstructural properties of the Pd2Si layer were investigated using Transmission Electron Microscopy (TEM), Energy-Dispersive X-ray Spectroscopy (EDS), X-ray Diffraction (XRD), X-ray reflectivity (XRR) and Secondary Ion Mass Spectrometry (SIMS). The work function of the silicide layer was measured on the fabricated metal(Pd2Si)-insulator-semiconductor (MIS) structures using Internal Photoemission Spectroscopy (IPS). The IPS technique was used to determine the barrier energy heights at the gate/dielectric (EBG) and dielectric/substrate (EBS) interfaces of the investigated Pd2Si/SiO2/Si system. The appropriate model allowing calculations of fractions of light absorbed by the gate and transmitted to the substrate was developed. The barrier energy from the Fermi level of the silicide gate and from the substrate valence band to the dielectric conduction band are estimated to be EBG = 4.11 ± 0.05 eV and EBS = 4.34 ± 0.05 eV, respectively. Taking the measured barrier height values and reported values of Si electron affinity (χSi = 4.05 eV) and Si band gap (EG = 1.12 eV), the electron affinity of the thermally grown oxide (SiO2) was determined to be χSiO2 = 0.83 ± 0.05 eV and the Pd2Si work function equal to ϕM = 4.94 ± 0.1 eV. It is shown that the application of a single, stoichiometric sputtering target allows to obtain thin Pd2Si layers with work function value resembling that for the bulk material.

Photovoltaic Solar Application Study of Cu0.5Zn0.5Se Thin Films by Chemical Bath Deposition Method

Inorganic ternary type materials are induced compound is worked as fundamental applications in transformation of the solar light energy into electrical energy. Copper zinc selenide thin films have been synthesized by chemical bath deposition method on to stainless steel plate. The configuration of fabricated cell is p-Cu0.5Zn0.5Se| NaOH(1M) + S(1M) + Na2S(1M) |C(graphite). The Photovoltaic cell characterization of the films is carried out by studying current–voltage characteristics in dark, capacitance–voltage in dark, barrier height measurements, power output, photoresponse and spectral response. The study shows that Cu0.5Zn0.5Se thin films are p-type conductivity. The junction ideality factor was found to be 2.93. The flat band potential was found to be -0.708V. The barrier height value was found to be 0.186 eV. The study of power output characteristic shows open circuit voltage, short circuit current, fill factor and efficiency were found to be 150 mV, 21 μA, 42.13%, and 0.63%, respectively. Photoresponse shows lighted ideality factor is 2.89. Spectral response shows the maximum current observed at 580 nm.

One-Step Synthesis of NbSe2/Nb-Doped-WSe2 Metal/Doped-Semiconductor van der Waals Heterostructures for Doping Controlled Ohmic Contact.

van der Waals heterostructures (vdWHs) of metallic (m-) and semiconducting (s-) transition-metal dichalcogenides (TMDs) exhibit an ideal metal/semiconductor (M/S) contact in a field-effect transistor. However, in the current two-step chemical vapor deposition process, the synthesis of m-TMD on pregrown s-TMD contaminates the van der Waals (vdW) interface and hinders the doping of s-TMD. Here, NbSe2/Nb-doped-WSe2 metal-doped-semiconductor (M/d-S) vdWHs are created via a one-step synthesis approach using a niobium molar ratio-controlled solution-phase precursor. The one-step growth approach synthesizes Nb-doped WSe2 with a controllable doping concentration and metal/doped-semiconductor vdWHs. The hole carrier concentration can be precisely controlled by controlling the Nb/(W + Nb) molar ratio in the precursor solution from ∼3 × 1011/cm2 at Nb-0% to ∼1.38 × 1012/cm2 at Nb-60%; correspondingly, the contact resistance RC value decreases from 10 888.78 at Nb-0% to 70.60 kΩ.μm at Nb-60%. The Schottky barrier height measurement in the Arrhenius plots of ln(Isat/T2) versus q/KBT demonstrated an ohmic contact in the NbSe2/WxNb1-xSe2 vdWHs. Combining p-doping in WSe2 and M/d-S vdWHs, the mobility (27.24 cm2 V-1 s-1) and on/off ratio (2.2 × 107) are increased 1238 and 4400 times, respectively, compared to that using the Cr/pure-WSe2 contact (0.022 cm2 V-1 s-1 and 5 × 103, respectively). Together, the RC value using the NbSe2 contact shows 2.46 kΩ.μm, which is ∼29 times lower than that of using a metal contact. This method is expected to guide the synthesis of various M/d-S vdWHs and applications in future high-performance integrated circuits.

Optical spectra and interfacial band offsets of pulse-laser-deposited metal-oxides: SnO2, TiO2, and ZnO

Transparent conducting oxides are electrically conductive materials with high optical transmittance in the visible region of the spectrum and are useful in a wide range of applications. In this study, the optical spectra of a set of single-phase transparent conducting oxides TiO2, ZnO, and SnO2 grown by pulse laser deposition are measured by vacuum ultraviolet spectroscopic ellipsometry and the optical bandgaps are determined to be 3.30 ± 0.05 eV, 3.13 ± 0.05 eV, and 3.95 ± 0.05 eV, respectively. Differences between these values and previous measurements are discussed. SnO2 and ZnO optical responses at the bandgap reveal that they are a direct bandgap, while TiO2 appears to show an indirect type. For the interfacial electronic characteristics, the internal photoemission measurement shows that the electronic barriers of these naturally n-type-doped metal oxides adjacent to an Al2O3 layer originate from the Fermi level in their conduction bands. The band offset determination shows that the barrier heights are similar and have a small internal field dependence. The work functions are then estimated from the measured barrier heights.

Probing Folding Barriers in High Throughput using Proteolysis and Yeast Display

A protein's primary sequence encodes its energy landscape, including the thermodynamic stability and dynamics of all accessible conformations. While the field has come a long way in understanding how thermodynamics are encoded, how the sequence encodes kinetic barriers is still poorly understood. Therefore, we are developing a novel combination of yeast display and proteolysis to select for high kinetic barriers. Proteolysis is an accessible and regularly used method that probes the energetics and dynamics of protein folding. Under the right conditions, proteolytic resistance arises solely from a large kinetic barrier to unfolding, allowing us to measure barrier heights directly. We have coupled proteolysis with yeast display, creating a high-throughput approach to select and monitor unfolding barrier heights, allowing us to systematically investigate how kinetic barrier height varies with changes in protein sequence. In addition to expanding our basic knowledge of protein folding, exploration of the relationship between sequence and kinetic barriers will allow for the development of long-lived drugs and shelf-stable detergents or a greater understanding of how pathogenic protein states arise.

Determination of the energetic resolution of Schottky barrier visualization via interface band structure and parallel momentum conservation

The energetic resolution of Schottky barrier visualization is determined by utilizing differences in interface band structures between the Au/Si(001) and Au/Si(111) non-epitaxial interfaces and parallel momentum conservation of the carriers. The visualization technique is based on ballistic electron emission microscopy and spectroscopy, where tens of thousands of spectra are collected on a grid and then fit to extract a spatially resolved map and histogram of the electrostatic barrier height. A resolution of 10 meV is determined from the minimal splitting and eventual merging of the histograms as the gold thickness decreases for the Au/Si(001) and Au/Si(111) samples. This splitting is below previously measured differences in barrier heights extracted from computational modeling of measured barrier height distributions from other interfaces.

Nanoscale Probing of Image-Potential States and Electron Transfer Doping in Borophene Polymorphs.

Because synthetic 2D materials are generally stabilized by interfacial coupling to growth substrates, direct probing of interfacial phenomena is critical for understanding their nanoscale structure and properties. Using field-emission resonance spectroscopy with an ultrahigh vacuum scanning tunneling microscope, we reveal Stark-shifted image-potential states of the v1/6 and v1/5 borophene polymorphs on Ag(111) with long lifetimes, suggesting high borophene lattice and interface quality. These image-potential states allow the local work function and interfacial charge transfer of borophene to be probed at the nanoscale and test the widely employed self-doping model of borophene. Supported by apparent barrier height measurements and density functional theory calculations, electron transfer doping occurs for both borophene phases from the Ag(111) substrate. In contradiction with the self-doping model, a higher electron transfer doping level occurs for denser v1/6 borophene compared to v1/5 borophene, thus revealing the importance of substrate effects on borophene electron transfer.

Photovoltaic Application Study of Zinc Telluride Thin Films Grown by Chemical Bath Deposition Method

Photovoltaic solar thin films zinc telluride studies on chemically deposited have been carried out to assess its suitability for use in the conversion of solar energy to electrical energy. The configuration of fabricated cell is n-ZnTe| NaOH (0.1M) + S (0.1M) + Na2S (0.1M)|C(graphite). The study shows that ZnTe thin films are n-type conductivity. The junction ideality factor was found to be 2.87. The flat band potential is found to be -0.652 V. The barrier height value was found to be 0.583 eV. The study of the power output characteristic shows open circuit voltage, short circuit current, fill factor and efficiency were found to be 150 mV, 25.6 μA, 24.86% and 0.49%, respectively. The photovoltaic cell characterization of the thin films is carried out by studying current-voltage characteristics in dark, capacitance-voltage in dark, barrier height measurements, power output characteristics.

Current–voltage characteristics and photovoltaic effect of a Au/ZnFe2O4/GaN Schottky junction

A Au/ZnFe2O4/GaN Schottky junction with a semiconducting heteroepitaxial ZnFe2O4 insertion layer was prepared by using a combined synthesis process of pulsed laser deposition and sputtering. The current–voltage (I–V) and capacitance–voltage (C–V) characteristics of the Schottky junction, as well as its photovoltaic effect, were investigated under dark conditions or ultraviolet (UV) or blue illumination. Insertion of the semiconducting ZnFe2O4 interlayer clearly induced an increase in the rectification ratio. Based on I–V measurements in a forward bias region, the barrier height and ideality factor of the Au/ZnFe2O4/GaN junction were estimated to be about 0.89 eV and 1.58, respectively. On the other hand, C–V measurement in a reversed bias region suggested a relatively larger barrier height of ∼1.32 eV. The Au/ZnFe2O4/GaN junction showed an open-circuit voltage of ∼0.5 V under UV light and a clear switching photocurrent behavior with UV ON/OFF. A schematic band model with two interfaces, Au/ZnFe2O4 and ZnFe2O4/GaN, was proposed to explain the measured barrier heights in forward and reverse bias regions.

Bias-voltage-dependent measurement of apparent barrier height on low-work-function thin film

Using a scanning tunneling microscope, we have examined the effect of the bias voltage on the apparent barrier height. The sample used in this study was a nitrogen-doped lanthanum hexaboride film. We experimentally proved that a linear relationship exists between the apparent barrier height and the sample bias voltage. As a consequence, we estimated the work function of the film to be 2.35 eV by theoretical fitting. This value is in good agreement with that obtained by photoemission spectroscopy in a previous study. Our results demonstrate that the work function calculated through apparent barrier height measurements is guaranteed to be highly reliable in spite of the simple one-dimensional model. We anticipate that the sensitivity of the barrier height to the sample work function can be utilized for elemental identification on surfaces with characteristic work functions.

Direct observation of potential phase at joining interface between p-MgO and n-MgFe2O4

Visualization of the depletion layer is a significant a guideline for the material design of gas sensors. We attempted to measure the potential barrier at the interface of core–shell microspheres composed of p-MgO/n-MgFe2O4/Fe2O3 from the inside out by means of Kelvin probe force microscopy (KPFM) as a first step to visualizing enlargement of the depletion layer. As determined by high-angle annular dark-field scanning transmission electron microscopy, ca. 70% of the microspheres were hollow with a wall thickness of ca. 200 nm. Elemental mapping revealed that the hollow particles were composed of ca. 20 nm of MgO, ca. 80 nm of MgFe2O4, and ca. 100 nm of Fe2O3. A difference of 0.2 V at the p-MgO/n-MgFe2O4 interface was clarified by KPFM measurements of the hollow particles, suggesting that this difference depends on the formation of a p–n junction. The potential barrier enlarged by the formation of a p–n junction was considered to increase the resistance in air (Ra), since the Ra of the core–shell hollow microspheres was higher than that of MgO, Fe2O3, MgO–Fe2O3, and MgO/MgFe2O4/Fe2O3 particles with irregular shapes. Measurement of the potential barrier height by KPFM is a promising potential approach to tuning the gas sensitivity of oxide semiconductors.