Effective Schottky Barrier Height Research Articles

Phosphorous ion implantation into NiGe layer for Ohmic contact formation on n-type Ge

Low-resistivity Ohmic contacts on n-type germanium (Ge) together with ideal rectifying characteristics for p-type Ge were achieved using phosphorous-ion-implanted nickel germanide (NiGe). A pre-germanidation process prior to ion implantation was employed, and subsequent drive-in annealing at low temperature was used to precisely control the phosphorous profile and optimize the process conditions. Very low contact resistance on n-type Ge was demonstrated by using low-temperature drive-in annealing at 300 °C. Further process optimization (ion dose of 2 × 1015 cm−2; drive-in annealing at 400 °C for 30 min) resulted in an effective electron Schottky barrier height as low as 0.09 eV for n-type Ge and an on/off current ratio of five orders of magnitude for p-type Ge. The proposed low-temperature contact formation process offers a significant advantage in source/drain contact formation for Ge-based high mobility n-channel transistors.

The Effect of Dielectric Capping on Few-Layer Phosphorene Transistors: Tuning the Schottky Barrier Heights

Phosphorene is a unique single elemental semiconductor with two-dimensional layered structures. In this letter, we study the transistor behavior on mechanically exfoliated few-layer phosphorene with the top-gate. We achieve a high ON-current of 144 mA/mm and hole mobility of 95.6 cm 2 /V·s. We deposit Al 2 O 3 by atomic layer deposition (ALD) and study the effects of dielectric capping. We observe that the polarity of the transistors alternated from p-type to ambipolar with Al 2 O 3 grown on the top. We attribute this transition to the changes for the effective Schottky barrier heights for both electrons and holes at the metal contact edges, which is originated from fixed charges in the ALD dielectric.

Numerical Simulation on the Influence of Via and Rear Emitters in MWT Solar Cells

In this paper, we analyze, by means of numerical simulations, metal wrap through (MWT) silicon solar cells without a rear emitter and/or via an emitter that feature a Schottky contact between the Ag metal and the p-base. We show how the effective Schottky barrier height affects both dark and illuminated properties of the cell. An equivalent electrical model for the dark analysis is proposed, which accounts for the shunting effects and the thermionic-emission current at Ag/p-base contact. We investigate the figures of merit of MWT solar cells for different via configurations, highlighting the influence of the Ag/p-base barrier height. Moreover, the influence of the rear busbar width, as well as of the operating temperature, is analyzed.

In–Ga–Zn–O MESFET with transparent amorphous Ru–Si–O Schottky barrier

AbstractRectifying transparent amorphous Ru–Si–O Schottky contacts to In–Ga–Zn–O have been fabricated by means of reactive sputtering without any annealing processes nor semiconductor surface treatments. The ideality factor, effective Schottky barrier height and rectification ratio are equal to 1.6, 0.9 eV and 105 A/A, respectively. Ru–Si–O/In–Ga–Zn–O Schottky barriers were employed as gate electrodes for In–Ga–Zn–O metal–semiconductor field‐effect transistors (MESFETs). MESFET devices exhibiting on‐to‐off current ratio at the level of 103 A/A in a voltage range of 2 V, with subthreshold swing equal to 420 mV/dec were demonstrated. A channel mobility of 7.36 cm2/V s was achieved. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Barrier inhomogeneities in titanium Schottky contacts formed on argon plasma etched p-type Si0.95Ge0.05

Electrical properties of Ti Schottky barrier diode fabricated on argon plasma etched p-type Si0.95Ge0.05 were studied using current–voltage (I–V) over a wide temperature range (100–300 K). The transport properties of the junction were analyzed by investigating the temperature dependence of both the effective Schottky barrier height (Φ0bp) and the ideality factor (n). It is shown that the ideality factor increases and the Schottky barrier height (SBH) decreases with decreasing temperature. This abnormal temperature dependence of the Φ0bp and n is explained on the basis of a thermionic emission conduction mechanism with Gaussian distributed barrier heights due to the barrier height inhomogeneities at the metal-p-Si0.95Ge0.05 interface. From the linear plot of the experimental SBH versus 1/T, a homogeneous SBH (\(\overline{\varPhi }_{0bp}\)) and a zero-bias standard deviation (σ0s) values of approximately 0.55 eV and 67 mV, respectively were computed. Furthermore the modified Richardson plot according to the Gaussian distribution model resulted in a homogeneous SBH (\(\overline{\varPhi }_{0bp}\)) and a Richardson constant (A*) of 0.55 eV and 35 A/cm2 K2, respectively. The A* value obtained from this plot is in very close agreement with the theoretical value of 32 A/cm2 K2 for p-type Si0.95Ge0.05. Furthermore, the SBH is found to decrease linearly as the interface states density (Nss) increases. It is proposed that the lateral inhomogeneities of the SBH are actually attributed to the distribution of the interface states which are in turns resulting from the plasma etching induced defects beneath the Si0.95Ge0.05 surface.

Direct Observation of Dipole Influence Induced by a Spin Coated Organic Interfacial Layer on Effective Schottky Barrier Height Modulation of Hg/Si Contact

A thin organic interfacial layer fabricated by a spin coating method based on 80% ethoxylated polyethylenimine (PEIE) solution is demonstrated to be able to effectively modulate the Schottky barrier height (SBH) of Hg/Si contact. A 0.28 eV reduction of effective electron affinity for the PEIE coated Si is observed by Kelvin probe measurement, which directly reveals the dipole influence induced by the PEIE layer. Capacitance-voltage and current-voltage measurements further demonstrate that the SBH modulation is dominated by the interlayer dipole effect.

Barrier inhomogeneities at vertically stacked graphene-based heterostructures

The integration of graphene and other atomically flat, two-dimensional materials has attracted much interest and been materialized very recently. An in-depth understanding of transport mechanisms in such heterostructures is essential. In this study, vertically stacked graphene-based heterostructure transistors were manufactured to elucidate the mechanism of electron injection at the interface. The temperature dependence of the electrical characteristics was investigated from 300 to 90 K. In a careful analysis of current-voltage characteristics, an unusual decrease in the effective Schottky barrier height and increase in the ideality factor were observed with decreasing temperature. A model of thermionic emission with a Gaussian distribution of barriers was able to precisely interpret the conduction mechanism. Furthermore, mapping of the effective Schottky barrier height is unmasked as a function of temperature and gate voltage. The results offer significant insight for the development of future layer-integration technology based on graphene-based heterostructures.

Schottky barrier height reduction for metal/n-InP by inserting ultra-thin atomic layer deposited high-k dielectrics

Fermi level pinning at metal/n-InP interface and effective Schottky barrier height (ФB,eff) were optimized by inserting ultrathin dielectrics in this work. Comparing the inserted monolayer and bilayer high-k dielectrics, we demonstrated that the introduction of bilayer dielectrics can further reduce ФB,eff (from 0.49 eV to 0.22 eV) than the monolayer dielectric (from 0.49 eV to 0.32 eV) even though the overall dielectric thickness was thicker. The additional dipole formed at high-k/high-k interfaces could be used to expound the mechanism. This work proposed an effective solution to reduce resistance contacts for InP based transistors and Schottky barrier transistors.

Band structure effect on the electron current oscillation in ultra-scaled GaSb Schottky MOSFET: tight-binding approach

This paper explores band structure effect on the quantum transport of a low-dimensional GaSb Schottky MOSFET (SBFET) for the implementation of III---V transistor with a low series resistance. Precise treatment of the full band structure is employed applying sp 3 d 5 s ∗ tight-binding (TB) formalism. A remarkable distinction between the thickness dependent effective masses extracted from the TB and the bulk values imply that the quantum confinement modifies the device performance. Strong transverse confinement leads to the effective Schottky barrier height increment. Owing to the adequate enhanced Schottky barriers at low drain voltages, a double barrier gate modulated potential well is formed along the channel. The double barrier profile creates a longitudinal quantum confinement and induces drain current oscillation at low temperatures. Significant factors that may affect the current oscillation are thoroughly investigated. Current oscillation is gradually smoothed out as the gate length shrinks down in ultra scaled structure. The results in this paper are paving a way to clarify the feasibility of this device in nanoscale regime.

Adaptive semiconductor/electrocatalyst junctions in water-splitting photoanodes

High-efficiency photoelectrochemical water-splitting devices require the integration of electrocatalysts (ECs) with light-absorbing semiconductors (SCs), but the energetics and charge-transfer processes at SC/EC interfaces are poorly understood. We fabricate model EC-coated single-crystal TiO2 electrodes and directly probe SC/EC interfaces in situ using two working electrodes to independently monitor and control the potential and current at both the SC and the EC. We discover that redox-active ion-permeable ECs such as Ni(OH)2 or NiOOH yield 'adaptive' SC/EC junctions where the effective Schottky barrier height changes in situ with the oxidation level of the EC. In contrast, dense, ion-impermeable IrOx ECs yield constant-barrier-height 'buried' junctions. Conversion of dense, thermally deposited NiOx on TiO2 into ion-permeable Ni(OH)2 or NiOOH correlated with increased apparent photovoltage and fill factor. These results provide new insight into the dynamic behaviour of SC/EC interfaces to guide the design of efficient SC/EC devices. They also illustrate a new class of adaptive semiconductor junctions.

Transport mechanisms and effective Schottky barrier height of ZnO/a-Si:H and ZnO/μc-Si:H heterojunction solar cells

The impact of boron doping on the p-layer of thin film silicon solar cells is assessed by measuring the effective Schottky barrier height of ZnO/a-Si:H and ZnO/μc-Si:H heterojunctions. A deviation from ideal diode characteristics is revealed by an increase of ideality factor with doping concentration. Higher current densities and lower effective Schottky barriers are evaluated for higher doping levels, resulting in increasingly Ohmic behaviour. This is attributed to an enhancement of tunneling through a thinner depletion region, as supported by computer simulations. Extracted barriers are in the range of 0.7–1 eV for the heterojunctions with rectifying behaviour.

Effects of plasma-induced defects on electrical characteristics of AlGaN/GaN heterostructure before and after low-temperature annealing

We investigated the electrical characteristics of an AlGaN/GaN heterostructure exposed to Ar plasma. In the near-surface region of the AlGaN/GaN heterostructure, we found that plasma-induced defects reduced the two-dimensional electron gas (2DEG) density and mobility at the AlGaN/GaN interface with increasing exposure time. The decrease in 2DEG density suggests that plasma-induced disordering partly extinguishes the piezo-polarization of the AlGaN layer, that the effective Schottky barrier height is increased by the introduction of negatively changed defects, or that the negatively charged defects induced during plasma exposure deactivate or compensate Si donors. In addition, we investigated the postannealing behavior of plasma-induced defects in the AlGaN/GaN heterostructure as well as in the n-GaN layer under an applied bias voltage.

Tight-binding analysis of current oscillation in nanoscale In0.53Ga0.47As Schottky MOSFET

A comprehensive study of band structure effect on the quantum transport of nanoscale In0.53Ga0.47As Schottky MOSFET for the implementation of III–V MOSFET with low source/drain series resistance is presented. Rigorous treatment of the full band structure in ultra-thin body MOSFET is employed using sp3d5s* tight-binding approach. Strong transverse confinement increases the energy of subbands and, indeed, the effective Schottky barrier height. Due to enhanced Schottky barriers and at low drain voltages, a double barrier gate modulated potential well is created along the channel that results in source-to-drain confinement of states. As tunnelling is the main current component in this device, longitudinal confinement induces drain current oscillation at low temperatures. Important factors that may affect current oscillation are demonstrated. Current oscillation that alters the normal performance of the device is investigated in nanowire Schottky MOSFET, as well. Additional quantum confinement in nanowire Schottky MOSFET provides higher effective Schottky barrier height than the double gate structure. Accordingly, the drain current oscillation is more apparent in nanowire Schottky MOSFET than in the double gate device and is gradually smoothed out as the gate length shrinks down in ultra-scaled structure. Effect of diffusive scattering on the quantum transport of the device is investigated, too. What is prominent in our result is that the drain current oscillations degrade as the channel mobility is decreased. The results in this paper are paving a way to elucidate the feasibility of this device in the nanoscale regime.

AlGaN/GaN Schottky Diode Fabricated by Au Free Process

An AlGaN/GaN Schottky diode is fabricated using an Au free process. Both ohmic and Schottky contact are studied. The ohmic contact results show low contact resistance and good surface morphology. The specific resistance (ρc) and contact resistance (Rc) of the ohmic contact are ~ 3.5×10-5 Ω×cm2 and 2.1 Ω·mm, respectively. Several current transport mechanisms are employed to analyze the measured I- V curves of the diode. The data have demonstrated that at a lower forward bias the combination of generation recombination and tunneling current mechanisms are dominant, whereas the thermionic emission mechanism becomes more significant at a higher forward bias. The effective Schottky barrier height is estimated to be 0.99 eV. The breakdown voltage of AlGaN/GaN Schottky diode is ~ 125 V.

Variation of Schottky barrier height induced by dopant segregation monitored by contact resistivity measurements

Change of contact resistivity (ρc) is monitored for evaluation of Schottky barrier height (SBH) variation induced by dopant segregation (DS). This method is particularly advantageous for metal–semiconductor contacts of small SBH, as it neither requires low-temperature measurement needed in current–voltage characterization of Schottky diodes nor is affected by reverse leakage current often troubling capacitance–voltage characterization. With PtSi contact to both n- and p-type diffusion regions, and the use of opposite or alike dopants implant into pre-formed PtSi films followed by drive-in anneal at different temperatures to induce DS at PtSi/Si interface, the formation of interfacial dipole is confirmed as the responsible cause for modification of effective SBHs thus the increase or decrease of ρc. A tentative explanation for the change of contact resistivity based on interfacial dipole theory is provided in this work. Influences and interplay of interfacial dipole and space charge on effective SBH are also discussed.

Tight-binding study of quantum transport in nanoscale GaAs Schottky MOSFET

This paper explores the band structure effect to elucidate the feasibility of an ultra-scaled GaAs Schottky MOSFET (SBFET) in a nanoscale regime. We have employed a 20-band sp3d5 s* tight-binding (TB) approach to compute E — K dispersion. The considerable difference between the extracted effective masses from the TB approach and bulk values implies that quantum confinement affects the device performance. Beside high injection velocity, the ultra-scaled GaAs SBFET suffers from a low conduction band DOS in the Γ valley that results in serious degradation of the gate capacitance. Quantum confinement also results in an increment of the effective Schottky barrier height (SBH). Enhanced Schottky barriers form a double barrier potential well along the channel that leads to resonant tunneling and alters the normal operation of the SBFET. Major factors that may lead to resonant tunneling are investigated. Resonant tunneling occurs at low temperatures and low drain voltages, and gradually diminishes as the channel thickness and the gate length scale down. Accordingly, the GaAs (100) SBFET has poor ballistic performance in nanoscale regime.

Performance assessment of nanoscale Schottky MOSFET as resonant tunnelling device: Non-equilibrium Green’s function formalism

A comprehensive study is performed on the electrical characteristics of Schottky barrier MOSFET (SBMOSFET) in nanoscale regime, by employing the non-equilibrium Green’s function (NEGF) approach. Quantum confinement results in the enhancement of effective Schottky barrier height (SBH). High enough Schottky barriers at the source/drain and the channel form a double barrier profile along the channel that results in the formation of resonance states. We have, for the first time, proposed a resonant tunnelling device based on SBMOSFET in which multiple resonance states are modulated by the gate voltage. Role of essential factors such as temperature, SBH, bias voltage and structural parameters on the feasibility of this device for silicon-based resonant tunnelling applications are extensively studied. Resonant tunnelling appears at low temperatures and low drain voltages and as a result negative differential resistance (NDR) is apparent in the transfer characteristic. Scaling down the gate length to 6 nm increases the peak-to-valley ratio (PVR) of the drain current. As the effective SBH reduces, the curvature of the double barrier profile is gradually diminished. Therefore, multiple resonant states are contributed to the current and consequently resonant tunnelling is smoothed out.

Ohmic contact to n-type Ge with compositional Ti nitride

Fermi-Level pinning at Ge surface results in high Schottky barrier height (SBH) for nearly all metal/n-Ge contacts. By varying composition of the TiNx, modulation of the SBH was demonstrated for TiNx/n-Ge contact. The effective SBH of the TiN0.1/n-Ge Schottky contact was found decreased to 0.45eV, as compared to the Ti/n-Ge contact SBH which was originally pinned at 0.56eV. Ohmic contact to n-type Ge was realized by increasing the nitrogen composition to x=0.8 in TiNx. Dipoles formed by the difference of the Pauling electronegativities for Ge and N at the contact interface is proposed to alleviate the Fermi-Level pinning effect.

Back-gate tuning of Schottky barrier height in graphene/zinc-oxide photodiodes

We demonstrate back-gate-tuning of the Schottky barrier height in graphene/zinc oxide photodiodes that are devised by a selective sputter-growth of ZnO on pre-patterned single-layer graphene sheets. The devices show a clear rectifying behavior (e.g., Schottky barrier height ∼0.65 eV and ideality factor ∼1.15) and an improvement in the photo-response via application of a back-gate voltage. The back-gate bias tunes the effective Schottky barrier-height and also promotes the activation of photo-excited carriers, which leads to an enhancement in the thermionic emission process.

Electrical characteristics and carrier transport mechanism for Ti/p-GaN Schottky diodes

The temperature dependence of the electrical characteristics of non-alloyed Ti/p-GaN Schottky diodes was examined using current-voltage-temperature, turn-on voltage-temperature, and series resistance-temperature measurements. The thermal coefficient (Kj) and characteristic temperature (T0) at T ≥ 293 K were determined to be −4.1 mV/K and 65.06 K, respectively. The effective Schottky barrier height (SBH) was also determined to be 2.1 (±0.03) eV, which was in good agreement with the theoretical value. The possible carrier transport mechanisms at the interface are described in terms of the thermally decreased energy-band gap of p-GaN layers, thermally increased deep-level acceptor and increased further-activated-shallow-level acceptor. These were confirmed by the thermally increased ideality factor and high tunnelling parameter.