Barrier Heights Of Schottky Contacts Research Articles

Comprehensive Analysis of E478 Single-Component Epoxy Resin and Tungsten-E478 Interface for Metallic-Polymer Composite Electron Source Applications.

This study provides comprehensive elemental, optical, and energy gap characteristics of the E478 single-component epoxy resin. This type of epoxy resin has imperative applications in medium voltage insulation and cold field emission of electrons. X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and hydrogen nuclear magnetic resonance (1H-NMR) were used to study the elemental and structural analyses, ultraviolet photoelectron spectroscopy (UPS) was used to obtain the local work function and the ionization potential energies, and ultraviolet/visible light spectroscopy (UV/VIS) was used to report the optical and energy gap characteristics of the epoxy resin being studied. Moreover, the UPS and UV/VIS analyses were merged to obtain the electron affinity of the E478 epoxy resin and to study the epoxy's energy band diagram and the tungsten-epoxy interface band structure. The results showed that the E478 epoxy resin is considered an n-type semiconductor of energy gap ∼3.94 eV, local work function ∼3.42 eV, ionization potential ∼6.10 eV, electron affinity ∼2.16 eV, and tungsten-epoxy Schottky contact barrier height ∼2.50 eV.

The Role of Nonidealities in the Scaling of MoS2 FETs

2-D material FETs hold the promise of excellent gate control, but the impact of nonidealities on their performance remains poorly understood. This is because of the need, so far, to use computationally intensive nonequilibrium Green’s function (NEGF) simulations. Here, we therefore use a semiclassical model to investigate the role of nonidealities in the scaling of back-gated (BG) and top-gated (TG) monolayer MoS2 FETs. We verify the electrostatics and transport of the semiclassical model with density functional theory-based NEGF simulations and calibrate nonidealities, such as interface traps ( ${D}_{\textsf {it}}$ ) and Schottky contact barrier height ( $\phi _{\textsf {SB}}$ ) to experimental monolayer and bilayer MoS2 FETs. We find that among the nonidealities, ${D}_{\textsf {it}}$ has the strongest subthreshold swing impact with 70 mV/dec obtainable in BG devices for a ${D}_{\textsf {it}}$ of $5\times {10}^{11}$ cm−2eV $^{-1}$ , an equivalent oxide thickness (EOT) of 1 nm, and a channel length ( ${L}_{\textsf {ch}}$ ) of 5 nm. For scaled EOT, $\phi _{\textsf {SB}}$ only strongly impacts ${I}_{ \mathrm{\scriptscriptstyle ON}}$ for the TG case, as the overlapping gate thins the Schottky barriers in the BG case. We show in TG devices that a spacer of only 5 nm results in a 1000-fold drop in ${I}_{ \mathrm{\scriptscriptstyle ON}}$ because of the nonidealities. We propose positive spacer oxide charge as a solution and show that a charge density of above 1013 cm−2 is required to fully recover the device performance.

Resistivity and Barrier Height of Nano-Resistors Made from Zr-Doped HfO2 High-K Dielectric on Si Wafer

Recently, a new type of nano-resistor device made from the high-k dielectric MOS structure was reported [1-5]. Nano-resistors are formed after a dielectric breakdown process. The nano-resistors are conductive paths that allow the current flowing from the substrate to the gate but not in the other direction [4]. In addition to light emission, it shows the antifuse- and diode-like characteristics [3,4]. For the antifuse application, it has a large current ratio of >105 between the “programmed” and “unprogrammed” states [3]. Previously, it was reported that the Schottky contact was formed between the conductive path and the Si substrate after the hard dielectric breakdown [6]. In this paper, authors investigated the resistivity of the nano-resistor surrounded by the Zr-doped HfO2 (ZrHfO) high-k dielectric and its Schottky contact barrier height with Si. The nano-resistors were formed from the dielectric breakdown of a MOS capacitor with the ZrHfO high-k film deposited on top of a p-type <100> Si (11-20 Ω∙cm) wafer. The detailed fabrication process of the 300 µm-diameter MOS capacitor and the nano-resistor formation step could be found in refs. 1-5. The sample surface was imaged with the JEOL JSM-7500F SEM after being stressed at the gate voltage (Vg ) of -20 V for 20 min. The I-V curve was measured with an Agilent 4155C semiconductor parameter analyzer. Figure 1 shows the top view of the device after being stressed at Vg = -20 V. Many tiny bumps are evenly distributed across the electrode surface. Each bump correspond to a nano-resistor of which the rough surface is formed from the high local temperature generated from the current flow [1]. The actual nano-resistor is located in the center of the bump and is much smaller than the size of the bump [5]. The total cross-sectional area ratio of bumps to the gate in the Fig. 1 structure is estimated to be approximately 0.04443. Figure 2 shows the I-V curve of the nano-resistor device. In the large voltage range, the current increases linearly with the increase of the magnitude of Vg (|Vg |). It has a constant resistance (Rs ) of 396.6 Ω. It is composed of several resistors connected in series: the bulk Si wafer, the Schottky contact between the Si and the nano-resistor, the nano-resistor, the ohmic contact between the nano-resistor and the gate, and the ITO gate electrode. The bulk Si resistance can be calculated based on ref. 7. At the large |Vg |, the Schottky contact resistance is negligibly small compared with other resistances. If the ohmic contact and gate electrode resistances are also neglected, the total resistance of the nano-resistors can be estimated. We assume that each nano-resistor has the same resistivity. Then, the resistivity of the nano-resistor is estimated to be 2673–7075 Ω∙cm, which is in the order of 103 Ω∙cm. At the low |Vg | range, we used the Schottky contact equation to fit the device’s I-V curve, as shown in equations 1 and 2 [7]. The voltage drop across the Schottky contact is taken as V-IRs . Figure 3 shows that the Schottky contact equation fits well with the experimental data and the nano-resistor has a barrier height of 0.66 eV on Si. In summary, the resistivity and barrier height of the nano-resistor can be estimated from the experimental data based on some basic assumption of the material properties. [1] Y. Kuo et al, APL, 102, 031117 (2013). [2] Y. Kuo, IEEE TED, 62, 3536-3540 (2015). [3] Y. Kuo, ECST, 67, 183 (2015). [4] Y. Kuo, ECST, 69, 23 (2015). [5] C.-C. Lin et al, APL, 106, 121107 (2015). [6] A. Avellán et al, IEEE EDL, 29, 366 (2008). [7] S. M. Sze et al, Physics of Semiconductor Devices, John Wiley & Sons, New Jersey (2007). Figure 1

On selenium p–n heterojunctions and Schottky contacts

Experimental capacitance–voltage data of selenium p–n heterojunctions on n-type Ge, Si, and GaN and flat-band barrier heights of selenium Schottky contacts are reanalyzed. The resulting built-in potentials of the p–n heterojunctions as well as the flat-band barrier heights of the Schottky contacts are explained by the well established concept of interface-induced gap states (IFIGS) where the interfacial electric dipoles are estimated by using the differences of the respective electronegativities. The analysis of the built-in potentials of the heterojunctions between crystalline p-Se films and n-Si and n-GaN substrates give an energy distance of 0.06 eV between the bulk Fermi level and the branch point of the IFIGS. The evaluation of the Schottky barrier heights reveals the IFIGS branch point of crystalline selenium to lie 0.03 ± 0.15 eV above the valence-band maximum. In summary, the valence-band offsets of c-Se/Si and c-Se/GaN heterostructures are estimated as 0.29 and 2.22 eV, respectively.

On the band-structure lineup at Schottky contacts and semiconductor heterostructures

The band-structure lineup at semiconductor interfaces is explained by the intrinsic interface-induced gap states (IFIGS) that derive from the complex band structures of the semiconductors. The barrier heights of metal–semiconductor or Schottky contacts as well as the band-edge offsets of semiconductor heterostructures are composed of a zero-charge-transfer term plus an electrostatic-dipole contribution which are determined by the IFIGS branch-point energies of the semiconductors and the electronegativity difference of the two materials in contact, respectively. This concept will be illustrated by experimental core-level shifts induced by metal adatoms on group-IV semiconductor surfaces. Choosing Si and SiO2 Schottky contacts and heterostructures as typical examples, it will be demonstrated that the IFIGS-and-electronegativity concept self-consistently explains the barrier heights of Schottky contacts and the valence-band offsets of heterostructures. The IFIGS-and-electronegativity concept also resolves the alleviation of the Fermi-level pinning by ultra-thin insulator interlayers in Schottky contacts. Finally, the modification of Schottky barriers by atomic interlayers will be discussed.

On the alleviation of Fermi-level pinning by ultrathin insulator layers in Schottky contacts

With a few exceptions, metal-semiconductor or Schottky contacts are rectifying. Intimate n-Ge Schottky contacts are the most extreme example in that their barrier heights are almost independent of the metal used. Such behavior is characterized as pinning of the Fermi level. Quite recently, ultrathin insulator layers placed between the metal and the semiconductor were found to lower the barrier heights of Schottky contacts and to increase their dependence on the metals used. In this way ohmic behavior was achieved without alloying. The barrier heights of intimate Schottky contacts and the valence-band offsets of heterostructures are well described by the intrinsic interface-induced gap states (IFIGS). Insulators fit in this concept because they are large-gap semiconductors. This article demonstrates that the IFIGS concept also explains the experimentally observed alleviation of the Fermi-level pinning or, as it is also addressed, the Fermi-level depinning in metal-ultrathin insulator-semiconductor or MUTIS structures. Their barrier heights are determined by the IFIGS branch-point energy of the semiconductor and the dependence of the barrier heights of the insulator Schottky contacts on the metals used. Furthermore, saturation of the semiconductor dangling bonds by, for example, sulfur or hydrogen adatoms prior to the deposition of the metals also reduces or increases the barrier heights of Schottky contacts irrespective of the metals applied. In other words, no alleviation of the Fermi-level pinning or depinning occurs. These modifications of the barrier heights are explained by the partial ionic character of the covalent bonds between the adatoms and the semiconductor atoms at the interface, i.e., by an extrinsic electric-dipole layer.

Analysis of degradation mechanisms in lattice-matched InAlN/GaN high-electron-mobility transistors

We address degradation aspects of lattice-matched unpassivated InAlN/GaN high-electron-mobility transistors (HEMTs). Stress conditions include an off-state stress, a semi-on stress (with a partially opened channel), and a negative gate bias stress (with source and drain contacts grounded). Degradation is analyzed by measuring the drain current, a threshold voltage, a Schottky contact barrier height, a gate leakage and an ideality factor, an access, and an intrinsic channel resistance, respectively. For the drain-gate bias &amp;lt;38 V parameters are only reversibly degraded due to charging of the pre-existing surface states. This is in a clear contrast to reported AlGaN/GaN HEMTs where an irreversible damage and a lattice relaxation have been found for similar conditions. For drain-gate biases over 38 V InAlN/GaN HEMTs show again only temporal changes for the negative gate bias stresses; however, irreversible damage was found for the off-state and for the semi-on stresses. Most severe changes, an increase in the intrinsic channel resistance by one order of magnitude and a decrease in the drain current by ∼70%, are found after the off-state ∼50 V drain-gate bias stresses. We conclude that in the off-state condition hot electrons may create defects or ionize deep states in the GaN buffer or at the InAlN/GaN interface. If an InAlN/GaN HEMT channel is opened during the stress, lack of the strain in the barrier layer is beneficial for enhancing the device stability.

On the explanation of the barrier heights of InP Schottky contacts by metal-induced gap states

The barrier heights of metal-semiconductor or Schottky contacts are explained by the continuum of metal-induced gap states (MIGSs). A verification of the theoretically predicted values requires experimental barrier heights of Schottky contacts, which are not only intimate, abrupt, and free of impurities but also laterally homogeneous. Such data may be obtained from current-voltage and capacitance-voltage characteristics. Results of corresponding studies with Ag, Au, Cr, Pd, and Ti contacts on InP were recently published. The barrier heights of the respective laterally homogeneous Schottky contacts evaluated from those experimental data quantitatively confirm the predictions of the MIGS theory.

On the electric-dipole contribution to the valence-band offsets in semiconductor-oxide heterostructures

The continua of interface-induced gap states (IFIGS) determine the band-structure lineup at semiconductor interfaces. Hence, both barrier heights of Schottky contacts and valence-band offsets in semiconductor heterostructures are composed of a zero-charge-transfer and an electric-dipole term. The analysis of experimental barrier heights and valence-band offsets yields IFIGS branch-point energies of 3.51±0.07eV for SiO2 and 2.98±0.26eV, 2.27±0.14, and 2.87±0.14eV for the high-κ oxides Al2O3, HfO2, and ZrO2, respectively. In the oxide heterostructures, the electric-dipole terms come up to 30% of the valence-band offsets and can thus not be neglected.

Schottky contact barrier height extraction by admittance measurement

Different from the conventional current-voltage and capacitance-voltage methods, Schottky contact barrier height extraction by admittance measurement is proposed and discussed in this paper. In this method, the barrier height can be simply extracted from the difference between the measured admittance at zero bias and a reasonably high forward bias. Both simulation results and experimental data demonstrate that the proposed method is effective not only for extraction of Schottky contacts with higher barrier heights (&amp;gt;0.4eV) but also for extraction of those with moderately lower barrier heights (0.2–0.4eV).

On the band structure lineup at interfaces of SiO2, Si3N4, and high-κ dielectrics

The interface-induced gap states (IFIGS) are the fundamental mechanism which determines the band structure lineup at semiconductor interfaces. The valence-band offsets of semiconductor heterostructures and the barrier heights of Schottky contacts are given by the branch-point energies of the IFIGS of the semiconductors and respective electric-dipole terms. The branch-point energies of SiO2, Si3N4, and of the high-κ dielectrics Al2O3, HfO2, and ZrO2 are determined as 3.99±0.10, 1.93±0.14, 3.23±0.42, 2.62±0.18, and ≈3.2eV, respectively, from experimental valence-band offsets of heterostructures of these insulators.

Barrier heights of Schottky contacts on strained AlGaN/GaN heterostructures: Determination and effect of metal work functions

Ir, Ni, and Re Schottky contacts on strained Al0.25Ga0.75N/GaN heterostructures are characterized using capacitance–voltage (C–V) and I–V techniques. Based on the measured C–V characteristics, two dimensional electron gas sheet carrier concentrations at the AlGaN/GaN interface and barrier heights of Ir, Ni, and Re Schottky contacts are calculated. The barrier heights of 1.12, 1.27, and 1.68 eV are obtained for Ir, Ni, and Re Schottky contacts, respectively. The results show that the barrier heights of Schottky contacts on strained AlGaN/GaN heterostructures are strongly dependent on the metal work functions. However, contrary to Schottky contacts on bulk AlGaN or GaN, the barrier height on strained AlGaN/GaN heterostructures is lower for a Schottky contact with a higher metal work function. This is attributed to the stronger wave function coupling between electrons in the Schottky metal and surface donor electrons. The I–V characteristics for Ir, Ni, and Re Schottky contacts confirm the results obtained by C–V characteristics.

Cryogenic processing of thin metal films

Cryogenic processing has been proven to be efficient in increasing Schottky contact barrier height, and significantly reducing device reverse leakage current. Metal-semiconductor-metal (MSM) photodetectors are widely used in optoelectronic integrated circuit (OEIC) receivers because of their compatibility with the preamplifier for their planar integration scheme, the minimum number of processing steps, high performance, and low cost. InGaAs/InP is usually chosen for the long wavelength application. However, there is always a potential problem of high dark current in an InGaAs/InP MSM photodetector due to the lower barrier height for such a material. In a recent study on Ag/InGaAs/InP contacts fabricated by a low temperature (LT) processing the Schottky barrier height was found to be as high as 0.64 eV. This value is more than double that of the same contact obtained by room temperature (RT) processing. Therefore, it is believed that the LT processing could greatly enhance the performance of a MSM photodetector. In this work, the effect of LT processing on the properties of thin metal films was investigated. Atomic force microscopy (AFM), transmission electron microscopy (TEM), and in-situ resistivity measurements were conducted.

The Influence of Annealing on Current-Voltage Characteristics of H2SeO3 Treated Al-nGaAs Schottky Contact

In this study the annealing effects on current–voltage and low-frequency noise characteristics of Al–nGaAs Schottky contact were investigated. Selenious acid treatment of GaAs surface prior Al deposition resulted in effective barrier height (φ*b) reduction up to 0.36 eV and to the Ohmic contact formation after annealing above 450 °C. SEM analysis revealed that Se passivation affected both metallisation morphology and interface reaction kinetic during the Al–GaAs anneals. Observed changes of the Schottky contact barrier height, low-frequency noise and thermostability are explained by the interface Se reactions with both GaAs and Al.

Electronic properties of ideal and interface-modified metal-semiconductor interfaces

The electronic properties of metal-semiconductor or Schottky contacts are characterized by their barrier heights. At ideal contacts, they are determined by the continuum of metal-induced gap states. Extrinsic interface defects and dipoles as well as interlayers may be present in real contacts and will modify the barrier heights. The zero-charge-transfer barrier height and a slope parameter describe the chemical trends of the barrier heights of Schottky contacts on a specific semiconductor. The zero-charge-transfer barrier heights may be calculated by using the empirical tight-binding method with universal parameters and the width of the dielectric band gaps and the slope parameters are given by the optical dielectric constants of the semiconductors. This is verified by comparison with numerical data from well-established theoretical approaches. Hydrogen doping of metal–diamond and metal–silicon interfaces changes their barrier heights with opposite sign. This is explained by a different orientation of H–C and H–Si interface dipoles. Ag and Pb/Si(111) contacts may be prepared with a ‘‘7×7’’ and a 1×1 interface structure. The difference of their barrier heights is explained by the electric dipole correlated with the stacking fault which is a characteristic of 7×7 reconstructions. Interlayers will also alter the barrier heights of Schottky contacts. Typical examples are SiO2 and Si3N4, i.e., MOS and MNS structures. Previous investigations found their barrier heights to vary as a function of the metals used. The chemical trends of these two data sets are described by the slope parameters predicted from the optical dielectric constants of SiO2 and Si3N4.

Schottky contact barrier height enhancement on p-type silicon by wet chemical etching

A wet chemical etch preceding the usual cleaning process has been found to yield Schottky barriers of high values on p-type silicon. This procedure produces a passivated surface layer which has resulted in Al/0-Si Schottky diodes with barrier height of 0.75 eV and ideality factor of 1.15. Measurements have confirmed the presence of electrically active donor-like states in this surface layer. The origin of the donor states is explained in terms of the deactivation of the boron acceptor by the formation ofH+B− pairs.

Pressure dependence of barrier heights of schottky contacts on silicon

physica status solidi (a)Volume 101, Issue 1 p. K29-K32 Short Note Pressure dependence of barrier heights of schottky contacts on silicon N. Balasubramanyam, N. Balasubramanyam Department of Physics, Indian Institute of Science, Bangalore Search for more papers by this authorVikram Kumar, Vikram Kumar Department of Physics, Indian Institute of Science, Bangalore Search for more papers by this author N. Balasubramanyam, N. Balasubramanyam Department of Physics, Indian Institute of Science, Bangalore Search for more papers by this authorVikram Kumar, Vikram Kumar Department of Physics, Indian Institute of Science, Bangalore Search for more papers by this author First published: 16 May 1987 https://doi.org/10.1002/pssa.2211010137Citations: 3 Bangalore 560012, India. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume101, Issue116 May 1987Pages K29-K32 RelatedInformation

Schottky contact barrier height modification by ion implantation of Al into GaAs

The barrier height of Al/GaAs Schottky contacts have been increased from 0.82 to 0.99 eV by the ion implantation of Al into GaAs prior to metal deposition. The contacts have lower leakage currents and higher breakdown voltages than contacts made on unimplanted samples. I-V, C-V, and photoresponse data will be presented to show clear evidence of barrier height increase. Carrier concentration profiling, scanning electron microscopy (SEM) and Auger analysis will also be used to show that the barrier height increase is due to the formation of a thin layer of AlGaAs by the Al implantation.