Barrier Height Measurements Research Articles

TiN x / HfO 2 interface dipole induced by oxygen scavenging

Electron barrier height measurements at TiNx/HfO2 interfaces in metal-insulator-metal structures using internal photoemission of electrons reveal a significant (≈1 eV, i.e., about 1/3 of the total barrier height) influence of the opposite electrode material, i.e., Hf versus TiNx. This effect is suggested to be caused by oxygen scavenging from HfO2 by the opposite Hf electrode resulting in generation of positive charges in the oxide above the metal electrode surfaces. Such a considerable interface dipole component demonstrates a principle that may be used to tune the barrier.

Predicting tidal flooding of urbanized embayments: A modeling framework and data requirements

Numerous urbanized embayments in California are at risk of flooding during extreme high tides caused by a combination of astronomical, meteorologic and climatic factors (e.g., El Niño), and the risk will increase as sea levels rise and storminess intensifies. Across California, the potential exists for billions of dollars in losses by 2100 and predictive inundation models will be relied upon at the local level to plan adaptation strategies and forecast localized flood impacts to support emergency management. However, the predictive skill of urban inundation models for extreme tide events has not been critically examined particularly in relation to data quality and flood mapping methodologies. With a case study of Newport Beach, California, we show that tidal flooding can be resolved along streets and at individual parcels using a 2D hydraulic inundation model that captures embayment amplification of the tide, overtopping of flood defenses, and overland flow along streets and into parcels. Furthermore, hydraulic models outperform equilibrium flood mapping methodologies which ignore hydraulic connectivity and are strongly biased towards over-prediction of flood extent. However, infrastructure geometry data including flood barriers, street and parcel elevations are crucial to accurate flood prediction. A real time kinematic (RTK) survey instrument with an error of approximately 1 cm (RMSE) is found to be suitable for barrier height measurement, but an error of approximately15 cm (RMSE) typical of aerial laser scanning or LiDAR is found to be inadequate. Finally, we note that the harbor waterfront in Newport Beach is lined by a patchwork of public and private parcels and flood barriers of varied designs and integrity. Careful attention to hydraulic connectivity (e.g., low points and gaps in barriers) is needed for successful flood prediction.

The direct measurement of energy barrier height at metal/ polyfluorene derivatives interface by internal photoemission spectroscopy

ABSTRACTWe have investigated the barrier height for electron injection at the cathode / polyflu-orene derivatives interface by the internal photoemission (IPE) spectroscopy techniques using the “electron only device” structure consisting of TiO2, electron transporting polyimide inter-layer (IL), and polyfluorene derivatives. We also estimated the barrier height by the current analysis based on the Schottky thermal emission current model, and it coincides well to the threshold energy of IPE result only when the energy is lower than 1.1eV. The measured barrier height obtained by IPE linearly increases with both the work-function of cathode materials. However, the slope parameter becomes less than 1 (~0.6) for poly (9,9-dioctylfluorene) (F8) probably due to the interfacial gap states. On the other hand, the slope parameter becomes very small (~0.18) for the poly (9,9-dioctylfluorene)-co- benzo- thiadiazole) (F8BT) probably due to the electron pinning at the cathode/ acceptor interface.

Characterization of Indium Segregation in Metalorganic Vapor Phase Epitaxy-Grown InGaP by Schottky Barrier Height Measurement

Surface/interface segregation of indium in InGaP layers grown by metalorganic vapor phase epitaxy has been studied. Al/InGaP Schottky barrier height (ΦB) measurement was used for the evaluation of the segregation. It is shown that ΦB of GaAs/InGaP/GaAs double heterostructure (DH) is larger than that of InGaP/GaAs single heterostructure (SH), suggesting the diffusion of indium into upper GaAs layer. It is shown that the indium segregation progresses at the initial stage of InGaP growth and saturates when the InGaP thickness reaches about 15 nm. Using the segregation model, we calculated the exchange coefficient of indium as 0.76 at 620 °C.

Electrical and physical characteristics of HfLaON-gated metal–oxide-semiconductor capacitors with various nitrogen concentration profiles

The comparative studies of electrical and physical characteristics of HfLaON-gated metal–oxide-semiconductor (MOS) capacitors with various nitrogen concentration profiles (NCPs) were investigated. Various NCPs in HfLaON gate dielectrics were adjusted by Hf 2La 2O 7 target sputtered in an ambient of modulated nitrogen flow. The related degradation mechanisms of various NCPs in HfLaON dielectrics have been investigated under various post-deposition annealing (PDA). The results indicate that by developing full nitrogen profile (FNP) incorporated into HfLaON dielectric enhances electrical characteristics, including oxide trap charge, interface trap density, and trap energy level. Detailed understand of current mechanisms of various NCPs incorporated into HfLaON dielectrics using current–voltage characteristics under various temperature measurements were investigated. Energy band diagram of MOS capacitor with Ta/HfLaON/SiO 2/P-Si(1 0 0) structure was demonstrated by the measurement of Schottky barrier height and the optical band gaps.

New Strategies for e‐Beam Characterization of Catalysts

AbstractBuilding on the success of aberration correction and the construction of in situ reaction chambers, electron microscopy is poised to make fresh advances in catalyst characterization. More profitable use should be made of photons both as input drivers and as output signals. Secondary electron imaging can provide extra information about the support structure. When collected in coincidence with primary beam energy losses, the secondary electron signal may even open the way to surface barrier height measurement at surface facets on individual nanoparticles.

Photoelectrochemical applications of In2Se3 thin films by chemical deposition

Indium selenide films have been synthesized by chemical bath deposition method onto stainless steel plate. The configuration of fabricated cell is n-In2Se3| NaOH(1 M) + S(1 M) + Na2S(1 M) |C(graphite). Characterization of the photoelectrochemical cell was carried out by studying X-ray diffraction, current–voltage and capacitance–voltage characteristics in the dark, barrier height measurements, power output, photoresponse and spectral response. The study shows that the In2Se3 thin films are n-type semiconductor. The junction ideality factor was found to be 3.24. The flat band potential and the barrier height were found to be 0.720 V and 0.196 eV, respectively. From the study of power output characteristics, open circuit voltage, short circuit current, fill factor and efficiency were found to be 310 mV, 20 μA, 37.64 and 0.61%, respectively. Photoresponse studies show that the lighted ideality factor is 2.78. Maximum current was observed at 575 nm.

Temperature-dependent barrier height in CdSe Schottky diode

This article reports the measurements of temperature-dependent barrier height (BH) of CdSe Schottky diodes. These diodes have been made by thermal evaporation technique on ITO glass and glass substrates at room temperature. The XRD measurements have been made and the average particle size has been calculated which comes out to be ~20 nm. The Au dots have been made for non-ohmic contacts. I–V characteristics have been measured at different temperatures (280–330 K). These characteristics obey the thermionic emission theory. The BH decreases and ideality factor increases with the increase in temperature. Richardson’s plot has been made and Richardson’s constant has been calculated which is less than the expected value. Capacitance measurements have been done at different frequencies and the interface states have been calculated. The results have been explained on the basis of BH inhomogeneities.

Microstructural and electrical characteristics of rapidly annealed Ni/Mo Schottky rectifiers on cleaned n-type GaN (0001) surface

We have investigated the electrical and microstructural properties of Ni/Mo Schottky rectifiers to n-type GaN by current–voltage (I–V) and transmission electron microscopy (TEM) before and after annealing at 600 °C. The obtained barrier height for as-deposited Ni/Mo contact is 0.66 eV. It is observed that the barrier height increases with annealing temperature up to 500 °C, reaching a maximum value of 0.75 eV at this temperature. However, the Schottky barrier height of the Ni/Mo Schottky contact slightly decreased to 0.67 eV (I–V) when the contact was annealed at 600 °C. According to the HRTEM, STEM and EDX analysis, the formation of Ga-Ni interfacial layer at the interface results in the accumulation of gallium vacancies near the surface of the GaN layer. This could be the reason for increase in barrier heights upon annealing at elevated temperatures. The variation in the measured barrier height after annealing at 600 °C may be due to the formation of native oxide layer at the interface compared to the 500 °C annealed contact.

Current Transport, Fermi Level Pinning, and Transient Behavior ofGroup-III Nitride Schottky Barriers

The current transport, Fermi level pinning and transient behavior of Group-III nitride Schottky barriers are reviewed. First, an overview of interface models is given. Then, the current transport mechanism in GaN, AlGaN, and InGaN Schottky barriers is discussed. We show that discrepancy in barrier height measurements in the I-V and the C-V methods, as well as large reverse leakage currents, can be explained by using the thin surface barrier (TSB) model. This understanding has led to a large leakage reduction by using an oxygen gettering process. Finally, the transient behavior of AlGaN/ GaN planar Schottky diodes is discussed to get insight into the surface-related current collapse phenomenon in AlGaN/GaN high electron mobility transistors (HEMTs). The responses are explained in terms of the dispersive transport caused by a time-continual random walk with hopping through surface states. This provides a new understanding of the current collapse.

Internal photoemission spectroscopy measurement of Alq 3/cathode interface by three layered electron only device

We have investigated the Schottky barrier height for electrons at aluminum tris (8-hydroxyquinoline) (Alq 3)/cathode interfaces by internal photoemission (IPE) measurement. A three layered device consisting of ITO/TiO 2/intermediate layer (IL)/Alq 3/cathode structure was used to fabricate the “electron-only device” and to reduce the equivalent thickness of TiO 2 and IL stack. The measured barrier heights were 0.86, 1.05, 1.3 and 1.55 eV for MgAg, Al, Ag and Au electrodes, and it gradually decreased with external voltage and it was explained as Schottky effect. Barrier height showed linear relationship with work-function and electronegativity of cathode materials. The slope parameter of 0.6 with electronegativity was attributed to the interfacial charge transfer through the metal-induced gap states at the cathode/Alq 3 interface.

Platinum Germanosilicide Contacts Formed on Strained and Relaxed $\hbox{Si}_{1 - x}\hbox{Ge}_{x}$ Layers

Contact resistivity is a key contributor to the parasitic series resistance of nanoscale MOSFETs. Since the contact resistivity is an exponential function of the Schottky barrier height, new contact materials that can provide smaller barrier heights to source-drain junctions are needed. Platinum germanosilicide (PtSi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> ) is of interest as a contact material to the recessed Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> junctions of p-channel MOSFETs due to the large work function of platinum silicide (PtSi). In this paper, we explore the impact of in-plane biaxial compressive strain in Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> layers on PtSi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> formation and the impact of the PtSi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> on the strain in Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> . The parameters considered in this paper include the Ge content, the thickness of the Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> epitaxial layer, and the PtSi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> thickness. The results show that the resistance, surface morphology, and the crystalline structure of the PtSi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> films are independent of the strain in the original Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> layer. The results also indicate that PtSi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> does not influence the strain in the Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> layer. The barrier-height measurements suggest the presence of Fermi-level pinning, and the pinning position is independent of the strain in the alloy, and it is primarily determined by the Ge concentration. As a result of Fermi-level pinning, hole Schottky barrier height of PtSi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> -Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> contacts is 0.1-0.2 eV higher than that of the PtSi-Si contacts.

Conducting atomic force microscopy studies of nanoscale cobalt silicide Schottky barriers on Si(111) and Si(100)

Cobalt silicide (CoSi2) islands have been formed by the deposition of thin films (∼0.1–0.3 nm) of cobalt on clean Si(111) and Si(100) substrates in ultrahigh vacuum (UHV) followed by annealing to ∼880 °C. Conducting atomic force microscopy has been performed on these islands to characterize and measure their current-voltage (I-V) characteristics. Current-voltage curves were analyzed using standard thermionic emission theory to obtain the Schottky barrier heights and ideality factors between the silicide islands and the silicon substrates. Current-voltage measurements were performed ex situ for one set of samples (termed “passivated surfaces”) where the silicon surface surrounding the islands was passivated with a native oxide. Other samples (termed “clean surfaces”) remained in UHV, while I-V curves were recorded. By comparing the barrier heights and ideality factors for islands on passivated surfaces and clean surfaces, the effects of the nonpassivated surfaces on conduction have been studied. The barrier heights measured from CoSi2 islands on clean surfaces are found to be ∼0.2–0.3 eV below barrier heights measured from similar islands on passivated surfaces. The main cause of the reduced Schottky barrier in the clean surface samples is attributed to Fermi level pinning by nonpassivated surface states of the clean silicon surface. However, the measured barrier heights of the islands are equivalent on both clean Si(111) and Si(100) surfaces, suggesting that the nonpassivated surface is influenced by cobalt impurities. Furthermore, the barrier heights of islands on the clean surfaces are lower than what can be explained by Fermi level pinning alone, suggesting the presence of additional reductions in the Schottky barrier heights. These variations are greater than what can be attributed to experimental error, and the additional barrier height lowering is primarily attributed to spreading resistance effects. Schottky barrier inhomogeneity is also identified as a possible cause of the additional barrier height lowering and nonideality in the Schottky contacts. Current-voltage measurements of the clean surface samples were also obtained at several temperatures. The barrier heights were found to decrease, and the ideality factors were found to increase with decreasing temperature. The dependence of the barrier height is attributed to the temperature variation of the Fermi level.

Structure and electronic properties of epitaxial fluorite-typeIrSi2on Si(001)

An epitaxially stabilized Ir-silicide phase was grown in ultrathin two-phase films on Si(001). Using transmission electron microscopy it was found to have the fluorite structure. Due to the misfit between this epitaxially stabilized phase and the silicon substrate, elastic and plastic strain relaxation can be observed. Optoelectronic measurements of transmission, resistivity, and Schottky barrier height show a transition from infrared absorbing to infrared transparent films depending on thickness and reaction temperature. First-principles calculations confirm the experimental data on the structure and electronic properties of fluorite-type Ir disilicide.

Molecular nanostructures with strong dipole moments on the Si(111)5 × 2-Au surface

Switchable organic molecules adsorbed on a silicon surface combine the flexibility and thelow cost of molecular electronic devices with the sophistication of modern silicontechnology. The first step towards creating such hybrid devices is the formation of regular,ordered patterns of molecules on a silicon surface. A stepped Si surface passivated by asub-monolayer of gold is found to provide a useful substrate for forming ordered molecularpatterns. Molecules with strong dipole moments, such as fluorophenols, form aone-dimensional molecular array on such a substrate by adsorbing on top of the step edges.Local barrier height measurement by scanning tunneling spectroscopy demonstrates thepossibilities to detect the direction of the dipole moment of an individual molecule.Polarization-dependent x-ray absorption spectroscopy reveals an oriented adsorption inboth the azimuthal and polar directions.

Photoelectrochemical studies of CdSe thin films deposited by dip method

Cadmium selenide photoelectrodes have been synthesized by chemical bath method onto stainless steel plate. The configuration of fabricated cell is n-CdSe|NaOH (1 M) + S (1 M) + Na 2S (1 M)|C (graphite). The photoelectrochemical cell characterization of the photoelectrodes is carried out by studying current–voltage characteristics in dark, capacitance–voltage in dark, barrier-height measurements, power output, photoresponse and spectral response. The junction ideality factor was found to be 3.23. The flat band potential was found to be 0.7 V. 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 was found to be 260 mV, 169 μA, 36.91% and 0.55%, respectively. Photoresponse shows lighted ideality factor is 4.06. Spectral response shows the maximum current observed at 730 nm.

Cu contact on NiSi substrate with a Ta/TaN barrier stack

The thermal and electrical stabilities of Cu contact on NiSi substrate with and without a Ta/TaN barrier stack in between were investigated. Four-point probe (FPP), X-ray diffraction (XRD), scanning electron microscopy (SEM), depth-profiling X-ray photoelectron spectroscopy (XPS), and Schottky barrier height (SBH) measurement were carried out to characterize the diffusion barrier properties. The SBH measurement provides a very sensitive method to characterize the diffusion barrier properties for the copper contact on NiSi/Si. The results show that the Ta/TaN stack can be both thermally and electrically stable after annealing at 450 °C for 30 min and it will have a potential application as a diffusion barrier for Cu contact on NiSi.

The Role of Band Bending in Affecting the Surface Recombination Velocities for Si(111) in Contact with Aqueous Acidic Electrolytes

The role of band bending in affecting surface recombination velocity measurements has been evaluated by combining barrier height data with charge-carrier lifetime measurements for Si(111) surfaces in contact with a variety of acidic aqueous electrolytes. Charge-carrier lifetimes and thus surface recombination velocities have been measured by contactless radio frequency photoconductivity decay techniques for long bulk lifetime n-Si(111) samples in contact with 11 M (40% by weight) NH4F(aq), buffered (pH = 5) HF(aq), 27 M (48% by weight) HF(aq), or concentrated 18 M H2SO4. Regardless of the sample history or surface condition, long charge-carrier lifetimes were observed for n-Si(111) surfaces in contact with 11 M NH4F(aq) or buffered HF(aq). On the basis of previous barrier height measurements, this behavior is consistent with the formation of an electrolyte-induced surface accumulation layer that reduces the rate of steady-state surface recombination even in the presence of a significant density of surface trap sites. A straightforward evaluation of the surface trap state density from the measured surface recombination velocities, S, is thus precluded for such Si/liquid contacts. In contrast, a wide range of S values, depending on the history of the sample and the state of the surface, were observed for n-Si(111) surfaces in contact with 27 M HF(aq). These results in conjunction with previously measured barrier height data indicate that the charge-carrier lifetimes measured for n-Si(111) in contact with 27 M HF(aq) can be directly correlated with the surface condition and the effective surface-state trap density. These conclusions were confirmed by measurements of the apparent S values of n-Si(111) surfaces in contact with various solutions in the presence of the known deep trap, Cu. For Si(111)/HF(aq) contacts, very high (≥920 ± 270 cm s-1) surface recombination velocities were observed when 0.16 mM (10 ppm) Cu2+ was in the solution and/or adsorbed onto the Si(111) surface as Cu0 deposits, whereas low (100 ± 75 or 225 ± 20 cm s-1) apparent surface recombination velocities were measured for Cu-contaminated Si(111) samples in contact with 0.16 mM (10 ppm) Cu2+-containing 11 M NH4F(aq) or BHF(aq) solutions, respectively.

Tunneling spectroscopy of ultrathin insulating films: CuN on Cu(100)

Scanning tunneling microscopy is used to characterize the electronic structure of 1 ML films of CuN on Cu(100). We find that CuN acts as an insulator with a band gap that exceeds 4eV. Measurements of the tunneling barrier height and image potential states indicate that the CuN work function is ∼0.9eV larger than bare Cu. This suggests a significant surface dipole, consistent with charge transfer predicted by theory. Our results indicate that CuN films are useful for controlling the electronic coupling between adsorbates and surface electron density on the nanometer scale.

Chemical deposition of ZnSe thin films: Photoelectrochemical applications

Abstract Zinc selenide films have been synthesized by chemical bath deposition method onto stainless steel plate. The configuration of fabricated cell is n-ZnSe|NaOH (1 M) + S (1 M) + Na2S (1 M)|C(graphite) .The photoelectrochemical 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 ZnSe thin films are n-type conductivity. The junction ideality factor was found to be 3.85. The flat band potential is found to be −0.530 V. The barrier height value was found to be 0.171 eV. The study of power output characteristic shows open circuit voltage, short circuit current, fill factor and efficiency was found to be 153 mV, 20 μA, 29.41% and 0.13%, respectively. Photoresponse shows lighted ideality factor is 6.78. Spectral response shows the maximum current observed at 440 nm.