Distribution Of Schottky Barrier Height Research Articles

On the temperature dependence of the current conduction mode in non-homogeneous Pt/n-GaN Schottky barrier diode

Forward current-voltage (I–V) measurements of Pt/n-GaN Schottky barrier diode (SBD) are investigated in a wide temperature range (80–400 K). The temperature dependence of the effective Schottky barrier height (SBH) and ideality factor are analyzed on the basis of the thermionic emission (TE) model by considering a double Gaussian distribution (DGD) of SBH due to the presence of barrier height inhomogeneities at the Pt/n-GaN interface. In the high temperature (HT) region (200–400 K), Pt/n-GaN SBD exhibits nearly an ideal behavior in accordance with the TE conduction mode. The obtained values of the homogeneous SBH Φ‾0bn = 1.33 eV and Richardson constant AHT* = 26.86 A cm−2 K−2are in agreement with the theoretical values for n-type GaN. In the low temperature (LT) region (80–160 K), the corresponding values Φ‾0bn = 0.94 eV and ALT* = 14.74 A cm−2 K−2 deduced within the TE mode deviate strongly from the ideal behavior. This deviation is further confirmed by the large ideality factor. In this work, we provide a strong evidence that the tunneling current including thermionic field emission (TFE) largely dominates the conduction mode at low temperature.

Analyzed electrical performance and induced interface passivation of fabricated Al/NTCDA/p-Si MIS–Schottky heterojunction

In this research, the significant role of 1,4,5,8-naphthalenetetracarboxylic-dianhydride, NTCDA, thin film on the Al/p-Si barrier under different temperatures is investigated. The structural and topographical properties of the thermally evaporated NTCDA thin film are investigated using a transmission electron microscope, TEM, and atomic force microscope, AFM, respectively, and elucidated that the fabricated films have a smooth nanocrystalline nature with an average crystallite size about 89 nm and average roughness about 3.15 nm. Furthermore, the current–voltage (I–V) characteristics of Al/NTCDA/p-Si/Al device are studied under dark conditions at different temperatures (313–383 K). The Schottky diode electronic parameters such as ideality factor, n, barrier height, ΦB, and reverse saturation current, Is, are calculated at each temperature. A clear increment of ΦB from 0.74 to 0.88 eV accompanied by a clear decrement of n values from 5.83 to 4.99 under increasing temperature (313–383) K is noticed. Due to the inhomogeneity of barrier height, the Gaussian distribution of Schottky barrier height is employed to estimate the mean value of barrier height and standard deviation and found to be 1.5 eV and 20 mV, respectively. The modified Richardson plot is used to estimate the modified Richardson constant and found to be 35.2 A cm−2 K−2 which is close to the known value of p-Si. Moreover, the conduction mechanism in forward and reverse biasing is explained in details. The modified Norde's function is employed for estimating the series resistance, Rs, and barrier height of the fabricated device at each temperature, where the values of Rs showed a decrement behavior from 3.564 to 1.165 kΩ upon increasing the temperature. The process of inserting NTCDA between electrode and p-Si influenced the distribution of interface states for MIS Schottky diode at different temperatures and is explained as a passivation process of the device's interface states.

Barrier Height Inhomogeneity in Mixed-Dimensional Graphene/Single CdSe Nanobelt Schottky Junctions

Mixed-dimensional graphene/single CdSe nanobelt (NB) Schottky junctions are fabricated, and the influence of Schottky barrier inhomogeneity on the electrical transport mechanism is investigated. The ideality factor increases and the zero-bias Schottky barrier height (SBH) decreases monotonically, as temperature decreases from 300 to 80 K. The temperature-dependent electrical transport characteristics can be explained by the SBH inhomogeneity. We use a spatial potential fluctuation model to analyze the conduction mechanism, where the SBH with a Gaussian distribution is assumed. The standard deviations of SBH distribution are up to 13.06% and 14.09% of the mean value of zero-bias SBH in 80–140 and 140–300 K, respectively, implying strong SBH inhomogeneity in typical graphene/CdSe NB junctions.

Barrier inhomogeneity in microscale Pt/MoS2 Schottky barrier diode

Temperature dependent electrical characterization of microscopic Pt/MoS2 Schottky diode fabricated using electron beam lithography has been studied. The diode exhibits rectifying current–voltage characteristics in the whole temperature range from room temperature to 80 K. As temperature decreases from 296 to 80 K, Schottky barrier height (SBH) decreases whereas ideality factor increases. The temperature dependence of barrier height of the diode is explained on the basis of barrier inhomogeneity model. Assuming the Gaussian distribution of SBH, the inhomogeneity level is found to be 64 and 102 meV in the temperature regions 80 K–140 K and 160 K–296 K, respectively. The present study can be useful in deeper understanding of electrical behavior of rectifying metal contacts to MoS2.

Investigation of electrical inhomogeneity in ZnO varistor ceramics based on electronic relaxations

Spatially non-uniform electrical performance in ZnO varistor ceramics, which restricts application for higher energy absorption capability, is investigated in terms of electronic relaxations corresponding to intrinsic point defects. Decreased breakdown field and nonlinear coefficient are observed from 135.5 V/mm and 53 in central area to 122.0 V/mm and 20 in peripheral area as well as significantly increased leakage current density from 3.4 μA/cm2 to 18.3 μA/cm2. From microstructure analysis, grain size distribution is found relatively homogeneous, suggesting that electrically non-uniform grain boundaries should be responsible for divergent electrical properties. Investigation via energy dispersive spectrometer (EDS) shows higher Zn/O ratio in peripheral area, indicating higher possibility of generating intrinsic point defects like zinc interstitials and oxygen vacancies. This is further verified via dielectric spectroscopy that the densities of zinc interstitials and oxygen vacancies are both larger in peripheral area than those in central area. Oxygen is easier to be removed from ZnO lattice and diffuse into atmosphere during high-temperature sintering process, resulting in larger amount of oxygen vacancies in peripheral area. Meanwhile, more zinc atoms are removed from lattice and form interstitials as a result of distortion of ZnO lattice in peripheral area. Increased donor density in peripheral area attributed by oxygen vacancies and zinc interstitials results in decreased Schottky barrier height. Non-uniform distribution of Schottky barrier height is the origin of overall electrical inhomogeneity.

Research on the growth of β-(AlGa)2O3 film and the analysis of electrical characteristics of Ni/Au Schottky contact using Tung's model

Single crystalline β-(AlGa)2O3 epilayer was grown on β-Ga2O3 (010) substrate using pulsed laser deposition. By high resolution X-ray diffraction and X-ray photoelectron spectroscopy measurements, the Al composition was determined to be 11%–13%, somewhat larger than that of target. In addition, Schottky diodes were fabricated on epitaxial β-(Al0.11Ga0.89)2O3 film using Ni/Au as the anode contacts and the electrical characteristics were performed in the temperature range from 300 K to 573 K. From the forward I-V curves, the Φb and n were obtained and they are both strongly dependent on the temperature, which was attributed to the inhomogeneous Schottky barrier height distribution. According to the Tung's model, the mean barrier height of 1.38 eV and A* of 46.52 Acm−2K−2 are extracted by the modified Richardson plot.

Ambipolar MoS2 Transistors by Nanoscale Tailoring of Schottky Barrier Using Oxygen Plasma Functionalization.

One of the main challenges to exploit molybdenum disulfide (MoS2) potentialities for the next-generation complementary metal oxide semiconductor (CMOS) technology is the realization of p-type or ambipolar field-effect transistors (FETs). Hole transport in MoS2 FETs is typically hampered by the high Schottky barrier height (SBH) for holes at source/drain contacts, due to the Fermi level pinning close to the conduction band. In this work, we show that the SBH of multilayer MoS2 surface can be tailored at nanoscale using soft O2 plasma treatments. The morphological, chemical, and electrical modifications of MoS2 surface under different plasma conditions were investigated by several microscopic and spectroscopic characterization techniques, including X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), conductive AFM (CAFM), aberration-corrected scanning transmission electron microscopy (STEM), and electron energy loss spectroscopy (EELS). Nanoscale current-voltage mapping by CAFM showed that the SBH maps can be conveniently tuned starting from a narrow SBH distribution (from 0.2 to 0.3 eV) in the case of pristine MoS2 to a broader distribution (from 0.2 to 0.8 eV) after 600 s O2 plasma treatment, which allows both electron and hole injection. This lateral inhomogeneity in the electrical properties was associated with variations of the incorporated oxygen concentration in the MoS2 multilayer surface, as shown by STEM/EELS analyses and confirmed by ab initio density functional theory (DFT) calculations. Back-gated multilayer MoS2 FETs, fabricated by self-aligned deposition of source/drain contacts in the O2 plasma functionalized areas, exhibit ambipolar current transport with on/off current ratio Ion/Ioff ≈ 103 and field-effect mobilities of 11.5 and 7.2 cm2 V-1 s-1 for electrons and holes, respectively. The electrical behavior of these novel ambipolar devices is discussed in terms of the peculiar current injection mechanisms in the O2 plasma functionalized MoS2 surface.

Strong Fermi-level pinning induced by argon inductively coupled plasma treatment and post-metal deposition annealing on 4H-SiC

The effect of pre–metal deposition cleaning on 4H-SiC Schottky barrier diodes (SBDs) by using Ar ion bombardment in an inductively coupled plasma (ICP) chamber was investigated. The ICP treatment produced a thin and Si-depleted amorphous layer on the SiC surface. Partial graphitization was observed in the amorphous layer after post-metal deposition (PMD) annealing. This interfacial layer strongly pinned the Schottky barrier height (SBH). PMD annealing at 500°C resulted in a constant SBH (approximately 1.1eV) and narrow SBH distribution (standard deviation<3meV). However, the amorphous layer was consumed after 600°C PMD annealing due to interfacial reactions. These results suggest that the Ar ion bombardment technique with a suitable thermal budget can be used to form relatively uniform SBDs.

Understanding Coulomb Scattering Mechanism in Monolayer MoS2 Channel in the Presence of h-BN Buffer Layer

As the thickness becomes thinner, the importance of Coulomb scattering in two-dimensional layered materials increases because of the close proximity between channel and interfacial layer and the reduced screening effects. The Coulomb scattering in the channel is usually obscured mainly by the Schottky barrier at the contact in the noise measurements. Here, we report low-temperature (T) noise measurements to understand the Coulomb scattering mechanism in the MoS2 channel in the presence of h-BN buffer layer on the silicon dioxide (SiO2) insulating layer. One essential measure in the noise analysis is the Coulomb scattering parameter (αSC) which is different for channel materials and electron excess doping concentrations. This was extracted exclusively from a 4-probe method by eliminating the Schottky contact effect. We found that the presence of h-BN on SiO2 provides the suppression of αSC twice, the reduction of interfacial traps density by 100 times, and the lowered Schottky barrier noise by 50 times compared to those on SiO2 at T = 25 K. These improvements enable us to successfully identify the main noise source in the channel, which is the trapping-detrapping process at gate dielectrics rather than the charged impurities localized at the channel, as confirmed by fitting the noise features to the carrier number and correlated mobility fluctuation model. Further, the reduction in contact noise at low temperature in our system is attributed to inhomogeneous distributed Schottky barrier height distribution in the metal-MoS2 contact region.

Tunable Schottky barrier and high responsivity in graphene/Si-nanotip optoelectronic device

We demonstrate tunable Schottky barrier height and record photo-responsivity in a new-concept device made of a single-layer CVD graphene transferred onto a matrix of nanotips patterned on n-type Si wafer. The original layout, where nano-sized graphene/Si heterojunctions alternate to graphene areas exposed to the electric field of the Si substrate, which acts both as diode cathode and transistor gate, results in a two-terminal barristor with single-bias control of the Schottky barrier. The nanotip patterning favors light absorption, and the enhancement of the electric field at the tip apex improves photo-charge separation and enables internal gain by impact ionization. These features render the device a photodetector with responsivity ( for white LED light at intensity) almost an order of magnitude higher than commercial photodiodes. We extensively characterize the voltage and the temperature dependence of the device parameters, and prove that the multi-junction approach does not add extra-inhomogeneity to the Schottky barrier height distribution. We also introduce a new phenomenological graphene/semiconductor diode equation, which well describes the experimental I–V characteristics both in forward and reverse bias.

Relating spatially resolved maps of the Schottky barrier height to metal/semiconductor interface composition

The Schottky barrier height (SBH) is mapped with nanoscale resolution at pure Au/Si(001) and mixed Au/Ag/Si(001) interfaces utilizing ballistic electron emission microscopy by acquiring and fitting spectra every 11.7 nm × 11.7 nm over a 1 μm × 1 μm area. The SBH distributions for the mixed interfaces are about four times broader than the pure gold interface and have a complex structure arising from the incomplete intermixing and its effects on the scattering of hot electrons. The maps of the barrier heights and amplitudes for the mixed samples are inhomogeneous with localization attributed to the disordered mixture of the Au and Ag. A method to calculate ratio of the Au to Ag Schottky barrier heights is presented and discussed in relationship to the interface composition. These results demonstrate how the Schottky barrier height is a function of position at the interface, and how mapping can capture the electrostatic nature of these and possibly other mixed metal–semiconductor interfaces.

Temperature Dependent Current Transport Mechanism in Graphene/Germanium Schottky Barrier Diode

We have investigated electrical properties of graphene/Ge Schottky barrier diode (SBD) fabricated on Ge film epitaxially grown on Si substrate. When decreasing temperature, barrier height decreased and ideality factor increased, implying their strong temperature dependency. From the conventional Richardson plot, Richardson constant was much less than the theoretical value for n-type Ge. Assuming Gaussian distribution of Schottky barrier height with mean Schottky barrier height and standard deviation, Richardson constant extracted from the modified Richardson plot was comparable to the theoretical value for n-type Ge. Thus, the abnormal temperature dependent Schottky behavior of graphene/Ge SBD could be associated with a considerable deviation from the ideal thermionic emission caused by Schottky barrier inhomogeneities.

Analysis of inhomogeneous barrier and capacitance parameters for Al/rubrene/n-GaAs (100) Schottky diodes

In this paper, 5,6,11,12-tetraphenylnaphthacene (rubrene) was prepared on n type GaAs (100) substrate by spin coating. The device parameters of Al/rubrene/n-GaAs (100) Schottky diode have been investigated by means of current–voltage (I–V) characteristics in the temperature range 100–300K by steps of 50K and capacitance–voltage (C–V) and conductance–voltage (G–V) characteristics at 1MHz and 300K. It was observed that ideality factors increased and barrier heights decreased with the decreasing temperature. The observed anomaly of temperature dependence of Schottky barrier height and ideality factor are explained by Gaussian distribution of Schottky barrier height in the same temperature ranges. Al/rubrene/n-GaAs Schottky barrier diode has been shown to have a Gaussian distribution with mean barrier height (Φ¯B) of 1.076eV and standard deviation (σs) of 0.119V. Schottky barrier height (ΦB), series resistance (Rs), and the density of interface trap states (Ns s) of the diode were calculated as 1.004eV, 1.18k Ω and 2.145×1011eV−1cm−2 for 1MHz, respectively.

Electronic properties of Al/p-Si/C70/Au MIS-type diode

The electrical characteristics of the Al/p-Si/C70/Au diode were investigated by current–voltage and capacitance–voltage measurements. The current–voltage characteristics confirm that the diode is a metal–insulator–semiconductor type device. The decrease in ideality factor and increase in barrier height values of the diode were observed with temperature. This behavior was explained on the basis of Schottky barrier height inhomogeneities. The zero-bias mean barrier height ϕ¯bo and Richardson values for the diode were found to be 1.06eV and 33.12A/cm2K2, respectively. The obtained Richardson constant (A*=33.12A/cm2K2) is in agreement with the theoretical value of A*=32A/cm2K2. The interface state density properties of the diode were analyzed and the shape of the interface state density is changed with temperature. The ϕB value obtained from C–V measurement is higher than that of ϕB value obtained from I–V measurements. The discrepancy between ϕB(C–V) and ϕB(I–V) values was explained by distribution of Schottky barrier height due the inhomogeneities.

Analysis of electrical properties and deep level defects in undoped GaN Schottky barrier diode

Electrical and deep level defects have been investigated in GaN Schottky barrier diode (SBD) in the temperature ranging from 125K to 425K. The study was carried out by combined current density–voltage (J–V), capacitance–voltage (C–V) and deep level transient spectroscopy (DLTS) characterization techniques. It is found that the ideality factor n of the diode decreases and the corresponding Schottky barrier height (SBH) increases with increasing temperature, which indicates the barrier in-homogeneity at metal/semiconductor interface. Thermionic emission with Gaussian distribution of SBHs is thought to be responsible for the electrical behavior of the diode over the temperature region. The possible explanation for this discrepancy in the estimated SBHs from J–V and C–V is presented. The DLTS measurement has revealed two deep level traps in GaN with activation energies Ec−0.23eV and Ec−0.45eV having different capture cross-sections. In addition, we observed that the reverse leakage current in GaN SBD above 275K is due to Frenkel–Poole emission (FPE). The estimated emission barrier height by FPE model is about ~0.25eV. Hence, the reverse leakage current is due to the emission of electrons from the trap state near the metal–semiconductor interface into a continuum of states, associated with conductive dislocations.

Thermal stability of tungsten and tungsten nitride Schottky contacts to AlGaN/GaN

Thin tungsten nitride (WNx) films were produced by reactive DC magnetron sputtering of tungsten in an Ar—N2 gas mixture. The films were used as Schottky contacts on AlGaN/GaN heterostructures. The Schottky behaviours of WNx contact was investigated under various annealing conditions by current-voltage (I—V) measurements. The results show that the gate leakage current was reduced to 10−6 A/cm2 when the N2 flow is 400 mL/min. The results also show that the WNx contact improved the thermal stability of Schottky contacts. Finally, the current transport mechanism in WNx/AlGaN/GaN Schottky diodes has been investigated by means of I—V characterisation technique at various temperatures between 300 K and 523 K. A TE model with a Gaussian distribution of Schottky barrier heights (SBHs) is thought to be responsible for the electrical behaviour at temperatures lower than 523 K.

快热退火对Co/n-Poly-SiGe肖特基结I-V-T特性的影响

On n-Si(100) substrates,the Si1-xGex films were deposited by RF magnetron sputtering technique.AES spectra determine that Ge content in the Si1-xGex film is 17% approxi-mately.The Si0.83Ge0.17 films were doped with phosphorus at high temperature through thermal diffusion to fabricate n-type polycrystalline films,that is,the n-poly-Si0.83Ge0.17.And a Co film was sputtered on it.Thus,the Co/n-poly-Si0.83Ge0.17/n-Si Schottky junctions were made.Rapid thermal annealing(RTA) was conducted on these junctions from 300 ℃ to 600 ℃.The variable temperature I-V testing has been performed on the annealed Co/n-poly-Si0.83Ge0.17 Schottky junctions.It is found that,with the test temperature increase,the Schottky barrier height(SBH) difference of samples annealed at different RTA temperatures becomes less.And the sample annealed at 500 ℃ has the least apparent SBH.As a whole,the SBHs increase and the apparent ideality factors decrease with the test temperature increasing.Based on the model of inhomogeneous distribution of SBH,a reasonable explanation has been fulfilled on the experimental data.

Correlation Between Barrier Heights and Ideality Factors of Ni/n-Ge (100) Schottky Barrier Diodes

We computed the homogeneous Schottky barrier height (SBH) at ideality factor (n) = 1.0 of Ni/nGe (100) Schottky diodes (SDs). The SDs were identically prepared by using resistive evaporation of Ni on n-Ge (100). The SBHs and n of these diodes (24 dots) were calculated from their experimental forward bias current-voltage (I-V ) and reverse bias capacitance-voltage (C-V ) measurements at room temperature. Even though the Schottky diodes were identically prepared, the values of the SBH from the I-V characteristics varied from 0.487 to 0.508 eV, the ideality factor varied from 1.34 to 1.53, and the SBH from the C 2 -V characteristics varied from 0.358 to 0.418 eV. The Gaussian fits of the experimental SBH distributions obtained from the C 2 -V and the I-V characteristics yielded mean SBH values of 0.401 ± 0.015 and 0.503 ± 0.006 eV, respectively. Furthermore, a homogeneous SBH value of approximately 0.535 eV was also computed from an extrapolation of a linear plot of the experimental SBHs versus the ideality factors. The homogeneous SBHs, rather than the eective SBHs, of individual contacts or mean values should be used to discuss the theories and the physical mechanisms that determine the SBHs of SDs.

Two Dimensional Imaging of the Laterally Inhomogeneous Au/4H-SiC Schottky Barrier by Conductive Atomic Force Microscopy

We present a novel approach based on conductive atomic force microscopy (c-AFM) for nano-scale mapping of the Schottky barrier height (SBH) between a semiconductor and an ultrathin (1-5 nm) metal film. The method was applied to characterize the uniformity of the Au/4H-SiC Schottky contact, which is attractive for applications due to the high reported (∼1.8 eV) SBH value. Since this system is very sensitive to the SiC surface preparation, we investigated the effect on the nano-scale SBH distribution of a ∼2 nm thick not uniform SiO2 layer. The macroscopic I-V characteristics on Au/SiC and Au/not uniform SiO2/SiC diodes showed that the interfacial oxide lowers the average SBH. The c-AFM investigation is carried out collecting arrays of I-V curves for different tip positions on 1μm×1μm area. From these curves, 2D SBH maps are obtained with 10- 20 nm spatial resolution and energy resolution &lt;0.1 eV. The laterally inhomogeneous character of the Au/SiC contact is demonstrated. In fact, a SBH distribution peaked at 1.8 eV and with tails from 1.6 eV to 2.1 eV is obtained. Moreover, in the presence of the not uniform oxide at the interface, the SBH distribution exhibits a 0.3 eV peak lowering and a broadening (tails from 1.1 eV to 2.1 eV).

Current transport mechanism of Au∕Ni∕GaN Schottky diodes at high temperatures

Current transport mechanism in Au∕Ni∕GaN Schottky diodes has been investigated using current-voltage characterization technique between 27 and 350°C. It is found that the ideality factor n of the diode decreases with increasing temperature when the temperature is lower than 230°C, and then increases with increasing temperature when the temperature is higher than 230°C. The corresponding Schottky barrier height (SBH) increases all through the temperature range. Thermionic-emission model with a Gaussian distribution of SBHs is thought to be responsible for the electrical behavior at temperatures lower than 230°C, while the generation-recombination (GR) process takes place in at temperatures above 230°C. The effective Richardson constant is determined to be 24.08Acm−2K−2, in excellent agreement with the theoretical value. The extrapolated activation energy of the GR process is determined to be 1.157eV. Based on the cathodoluminescence measurements, it is suggested that the deep level defects inducing yellow luminescence facilitate the GR process of the current transport in the diodes.