Schottky Barrier Height Reduction Research Articles

The Role of Carbon and Dysprosium in Ni[Dy]Si:C Contacts for Schottky-Barrier Height Reduction and Application in N-Channel MOSFETs With Si:C Source/Drain Stressors

We clarify the role of carbon and dysprosium in nickel-dysprosium-silicide (Ni[Dy]Si:C) contacts formed on silicon:carbon (Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-</sub> yCy or Si:C) for Schottky-barrier height (SBH) reduction. Carbon-induced energy bandgap Eg narrowing and the segregation of dysprosium (Dy) at the Ni[Dy]Si:C/Si:C interface were shown to be responsible for SBH reduction in this paper. First, we show that electron barrier height (PhiBN) reduction of up to 69 meV (or 10.3%) for NiSi can be achieved with the scaling of substitutional carbon C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sub</sub> concentration from 0% to 1.0%. Second, new evidence revealing the segregation of Dy-based interlayer at the Ni[Dy]Si:C/Si:C interface and an additional 321 meV (or 53%) reduction in PhiBN for NiSi:C are presented. This could be due to charge transfer at the Ni[Dy]Si:C/Si:C interface. The successful modulation of PhiBN for Ni[Dy]S:C translates to an effective 41% reduction in device R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">EXT</sub> , resulting in improved drive current performance. This opens new avenues to optimize the Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-y</sub> C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> contact interface for extending transistor performance in future technological generations.

Selenium Segregation for Lowering the Contact Resistance in Ultrathin-Body MOSFETs With Fully Metallized Source/Drain

We report the first integration of selenium (Se) segregation contact technology in ultrathin-body (UTB) n-MOSFET featuring Ni fully silicided source and drain. During the Ni silicidation process, the implanted Se segregated at the NiSi-n-Si interface, leading to significant reduction of Schottky barrier height and contact resistance. The UTB n-MOSFETs integrated with Se segregation (SeS) contact technology show significant external series resistance reduction and drive current performance enhancement. Drain-induced barrier lowering and gate leakage current density are not adversely affected by the SeS process.

An Anomalous Gain Mechanism in GaN Schottky Barrier Ultraviolet Photodetectors

The gain mechanism in GaN Schottky barrier ultraviolet photodetectors is investigated by focused light beam. When the incident light illuminates the central region of the Schottky contact electrode, the responsivity changes very little with the increase of reverse bias voltage. However, when the incident light illuminates the edge region of the electrode, the responsivity increases remarkably with the increase of reverse bias voltage, and the corresponding quantum efficiency could be even higher than 100%. It is proposed that the surface states near the edge of the electrode may lead to a reduction of effective Schottky barrier height and an enhancement of electron injection, resulting in the anomalous gain.

Novel Aluminum Segregation at NiSi/ ${p}^{+}$-Si Source/Drain Contact for Drive Current Enhancement in $P$-Channel FinFETs

This letter reports the first demonstration of the integration of nickel-silicide (NiSi) source/drain (S/D) contact technology with a novel aluminum (Al) segregation at the NiSi/p +-Si interface in the S/D of p-channel FinFETs to reduce contact resistance. This leads to reduction in parasitic series resistance. We show that the addition of a low-dose (2times1014 atom/cm2) Al ion implant step in the Si S/D of p-channel FinFETs could achieve ~ 19% enhancement in drive current. This is attributed to the reduction in effective Schottky barrier height of holes at NiSi/p+-Si interface, from ~ 0.4 to ~ 0.12 eV, using Al segregation.

Hydrogen sensors based on Pt‐AlGaN/GaN back‐to‐back Schottky diode

AbstractIn this paper, platinum (Pt) with a thickness of 45 nm was sputtered on the surface of AlGaN/GaN heterostructure to form the Schottky contact and the back‐to‐back Schottky diodes were characterized for H2 sensing at room temperature. Both the forward and reverse current of the devices increased with exposure to H2 gas, which was attributed to Schottky barrier height reduction caused by hydrogen absorption in the catalytic metals. A shift of 0.7 V at 297 K was obtained at a fixed forward current of 0.1 mA after switching from N2 to 40% H2 in N2. The sensor's responses under different concentrations from 2500 ppm H2 to 40% H2 in N2 at 297 K were investigated. Time response of the sensor at a fixed bias of 1 V was given. Finally, the decrease of the Schottky barrier height and the sensitivity of the sensor were calculated. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Thermodynamic and Kinetic Analysis of Hydrogen Sensing in Pt/AlGaN/GaN Schottky Diodes at High Temperatures

Schottky diodes on AlGaN/GaN heterostructures with Pt catalytic metal are fabricated and characterized for hydrogen sensing at a wide range of temperature and hydrogen concentration. The thermodynamic and kinetic processes of hydrogen adsorption/desorption at Pt/AlGaN are analyzed based on their steady and transient state sensing characteristics. The devices have great hydrogen detection capability even at sub-ppm level reliably at temperatures up to 800. Both forward and reverse currents of Schottky diodes increase with exposure to containing ambient, which is attributed to the reduction of Schottky barrier heights resulted by hydrogen absorption at Pt/AlGaN. As temperature increases, the device sensitivity () is improved due to the more effective dissociation, but starts saturating from 600. The coverage of hydrogen at the Pt/AlGaN interface exhibits the same trend as and . The thermodynamic process of hydrogen adsorption in Pt/AlGaN is endothermic with an adsorption enthalpy of 21 . The adsorption time constant shortens as the temperature or the concentration increases. On the other hand, the desorption time constant exhibits opposite trend on the temperature and concentration. The absolute magnitudes of the activation energies for hydrogen adsorption/desertion at Pt/AlGaN increase with the concentration.

High temperature sensing characteristics of a high performance Pd/AlGaN/GaN Schottky diode hydrogen sensor obtained by oxygen gettering

AbstractHigh temperature sensing characteristics of a Pd/AlGaN/GaN Schottky diode hydrogen sensor were investigated. By applying an oxygen gettering process, the diode showed very small leakage currents even at elevated temperatures. On exposure to 10 Torr hydrogen in an air ambient (200 Torr), the diode showed a large current change of four orders of magnitude. The observed sensing behaviour could be fitted to a theory based on the sensing mechanism involving Schottky barrier height reduction due to interface dipole formation by atomic hydrogen. The diode showed much improved characteristics at 110 °C than at room temperature. This surprising result is explained in terms of the current transport mechanism. The diode showed much better sensing characteristics than those of GaAs and InP. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Dopant Condensation beyond Solubility Limit in the Vicinity of Silicon/Silicide Interface Based on First-Principles Calculations

ABSTRACTIn the trend of scaling down metal-oxide-semiconductor field effect transistors (MOSFETs), reduction of contact resistance at the silicide/silicon (Si) interface will be essential for higher performance. Nickel silicide (NiSi) is considered as a substi-tute for a present electrode material in MOSFETs, cobalt silicide (CoSi2), because silicidation temperature can be reduced as compared with the case of the conventional CoSi2. Hence, we have focused on the NiSi/Si Schottky interface. An ordinary method to increase the dopant concentration at the interface is ion implantation before silicidation process. The dopant atoms are consequently condensed around the interface by snowplow effect, leading to the effective lowering of the Schottky bar-rier height (SBH) because of the band bending enhancement of the Si layer. However, this band bending technique does not reduce the SBH in further scaled MOSFETs. In this context, we studied another possibility of SBH modulation technique, based on the first-principles calculations. Throughout our calculations, we found that a large atomic-scale dipole between impurity and silicide atoms is generated across the interface. Impurity atoms are expected to be condensed because of a large energy gain at the interfaces, leading to the dramatic reduction of the SBH. Based on these results, we proposed a novel di-pole comforting Schottky (DCS) junction. We have also found that the thickness of the Si layer interfacing with the NiSi layer can be 1nm or less. In the present work, we applied this idea to the actual process through experimental techniques. The calculated results suggest that B implantation after silicidation leads to larger B concentration at the interface than that before silicidation, and thereby larger SBH modulation due to interface dipoles can be produced. Then, the NiSi/Si Schottky diodes were formed by ion implantation after silicidation process for dopants (As, B). We evaluated the interface dipoles contribution to the measured SBH reduction. As a result, the dopant atoms were found to be condensed beyond solubility limits on the interface Si side and we confirmed the generated interface dipoles actually reduces the SBT. Furthermore, we explored the other possibility of another type of impurity atoms applicable to the DCS junction. Among some other impurity atoms (Al, In, Mg), the calculated SBH modulation due to dipoles generated around these impurity atoms were found to be further enhanced in some cases. Based on these understandings, we propose a principle for choosing dopants towards ulti-mate lowering of the contact resistance in ultimately scaled MOSFETs.

Effective Schottky Barrier Height Reduction Using Sulfur or Selenium at the NiSi/n-Si (100) Interface for Low Resistance Contacts

We explore a novel integration approach that introduces valence-mending adsorbates such as sulfur (S) or selenium (Se) by ion implantation and prior to nickel silicidation for the effective reduction of contact resistance and Schottky barrier (SB) height at the NiSi/n-Si interface. While a low SB height of ~0.12 eV can be obtained for NiSi formed on S-implanted n-Si, the insertion of a 1000degC anneal prior to silicidation leads to S out-diffusion and loss of SB modulation effects. We demonstrate that Se-implanted Si does not suffer from Se outdiffusion even after a 1000degC anneal, and subsequent Ni silicidation formed an excellent ohmic contact with a low SB height of 0.13 eV. Se segregation at the NiSi/n-Si (100) interface occurred. Implantation of Se and its segregation at the NiSi/n-Si interface is a simple and promising approach for achieving reduced SB height and contact resistance in future high-performance n-channel field-effect transistors.

Silicidation of Ni(Yb) Film on Si(001)

The influence of the addition of Yb to Ni on the silicidation of Ni was investigated. The Ni(Yb) film was deposited on a Si(001) substrate by co-sputtering, and silicidation was performed by rapid thermal annealing (RTA). After silicidation, the sheet resistance of the silicide film was measured by the four-point probe method. X-ray diffraction and micro-Raman spectroscopy were employed to identify the silicide phases, and the redistribution of Yb after RTA was characterized by Rutherford backscattering spectrometry and Auger electron spectroscopy. The influence of the Yb addition on the Schottky barrier height (SBH) of the silicide/Si diode was examined by current–voltage measurements. The experimental results reveal that the addition of Yb can suppress the formation of the high-resistivity Ni2Si phase, but the formation of low-resistivity NiSi phase is not affected. Furthermore, after silicidation, most of the Yb atoms accumulate in the surface layer and only a small number of Yb atoms pile up at the silicide/Si(001) interface. It is believed that the accumulation of a small amount of Yb at the silicide/Si(001) interface results in the SBH reduction observed in the Ni(Yb)Si/Si diode.

Hydrogen sensing characteristics and mechanism of Pd∕AlGaN∕GaN Schottky diodes subjected to oxygen gettering

Hydrogen sensing characteristics in vacuum and in air were investigated on Pd Schottky diodes that were formed on AlGaN∕GaN two-dimensional electron gas wafer and subjected to a surface control process for oxygen gettering. By applying the surface control process, leakage currents in Pd∕AlGaN∕GaN Schottky diode were greatly reduced. Such diodes showed high hydrogen detection sensitivities and fast turn-on and -off characteristics in air, although they showed very slow turn-off behavior in vacuum. From detailed measurements of current-voltage (I-V), capacitance-voltage (C-V), and current transient characteristics, the sensing mechanism was explained in terms of Schottky barrier height reduction caused by formation of interface dipole by atomic hydrogen. It was shown that dipole formation is controlled in air by the Langmuir isotherm type adsorption behavior, including the reaction between atomic hydrogen and oxygen. Discrepancies in Schottky barrier height values deduced from I-V and C-V measurements have indicated that current transport is not by the standard thermionic emission process, but by the thermionic field emission process through the thin surface barrier (TSB) in accordance with the TSB model.

Sensing dynamics and mechanism of a Pd/AlGaN/GaN Schottky diode type hydrogen sensor

Hydrogen sensing characteristics of surface-controlled Pd/AlGaN/GaN Schottky diodes were investigated in air. Sensors showed high detection sensitivities and fast turn-on and turn-off characteristics. Sensing dynamics and mechanism were explained in terms of Schottky barrier height reduction due to hydrogen-induced interface dipole. Here, the dipole formation is controlled by the Langmuir isotherm including an oxygen reaction, and current transport is due to thermionic field emission. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Transfer matrix method modelling of inhomogeneous Schottky barrier diodes on silicon carbide

The paper presents a novel modelling technique for the static characteristics of power Schottky barrier diodes on SiC. Starting from an accurate and physically sound estimation of the transmission coefficient for the electrons movement across the Schottky barrier, the forward and reverse bias static current is evaluated and compared to experimental results. In order to properly reproduce experimental results, an inhomogeneous parallel conduction description of the Schottky barrier is shown to be required in reverse bias. Furthermore, consistently with previous work, a Schottky barrier height reduction is observed in moving from forward to reverse bias.

High-reflectivity Al-Pt nanostructured Ohmic contact to p-GaN

The effect of nanoscale Pt islands on the electrical characteristics of contacts to p-type gallium nitride (GaN) has been investigated to explore the feasibility for the flip-chip configuration light-emitting diodes (LEDs) using an Al-based reflector. An as-deposited Al contact to p-GaN with a net hole concentration of 3times1017cm-3 was rectifying. However, an Al contact with nanoscale Pt islands at the interface exhibited ohmic behavior. A specific contact resistivity of 2.1times10-3Omegamiddotcm2 and a reflectance of 84% at 460 nm were measured for the Al contact with nanoscale Pt islands. Current-voltage temperature measurements revealed a Schottky barrier height reduction from 0.80 eV for the Al contact to 0.58 eV for the Al contact with nanoscale Pt islands. The barrier height reduction may be attributed to electric field enhancement and the enhanced tunneling due to the presence of the nanoscale Pt islands. This will offer an additional silver-free option for the p-type ohmic contact in flip-chip configuration LEDs. Theory suggests that the ohmic contact characteristics may be improved further with smaller Pt islands that will enhance tunneling across the interface with the GaN and in the vicinity of the Pt-Al interface

Drivability improvement in Schottky barrier source/drain MOSFETs with strained-Si channel by Schottky barrier height reduction

Due to an extra barrier between source and channel, the drivability of Schottky barrier source/drain MOSFETs (SBMOSFETs) is smaller than that of conventional transistors. To reach the drivability comparable to the conventional MOSFET, the Schottky barrier height (SBH) should be lower than a critical value. It is expected that SBH can be effectively reduced by a bi-axially strain on Si. In this letter, p-channel MOSFETs with PtSi Schottky barrier source/drain, HfAlO gate dielectric, HfN/TaN metal gate and strained-Si channel are demonstrated for the first time using a simplified low temperature process. Devices with the channel length of 4μm have the drain current of 9.5μA/μm and the transconductance of 14μS/μm at Vgs−Vth=Vds=−1V. Compared to the cubic Si counterpart, the drain current and the transconductance are improved up to 2.7 and 3.1 times respectively. The improvement is believed to arising from the reduced barrier height of the PtSi/strained-Si contact and the enhanced hole mobility in the strained-Si channel.

Formation of low resistance nonalloyed ohmic contacts to p‐type GaN by KrF laser irradiation

AbstractKrF excimer‐laser‐irradiation treatment in a N2 atmosphere is introduced to improve the electrical properties of p ‐type GaN and so to form low resistance nonalloyed Ni/Au ohmic contacts. The as‐grown sample exhibits non‐linear electrical behavior. However, the samples laser‐annealed in N2 ambient become ohmic with specific contact resistance of 8.9(±0.6)×10–5 Ωcm2. Hall measurement and current‐voltage‐temperature results show that the laser irradiation is effective in increasing a hole concentration in the surface region of p ‐GaN, leading to both the enhancement in field emission and the reduction of the effective Schottky barrier heights at the metal‐semiconductor interface. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Low-resistance Ti/n-type Si(100) Contacts by Monolayer Se Passivation

Low-resistance contacts fabricated by selenium passivation between Ti and n-type Si(100) substrates have been characterized by low-temperature I-V, four-point probe and circular transmission line methods. The Ti-Si contacts on Se- passivated samples demonstrate a significant reduction in Schottky barrier height over control samples in low- temperature I-V. Sheet resistance of the contacts on Se- passivated 1019 cm-3 doped n-type Si(100) substrates shows a 30% reduction as compared with control samples. Accordingly, the extracted contact resistance decreases by about one order of magnitude for samples with different Ti thicknesses and different annealing temperatures. A 125%-2900% reduction in contact resistivity is achieved by Se passivation on highly- doped n-type SOI substrates with 500 Aå un-doped Si buffer layer. The reduction in contact resistance is attributed to the minimization of interface states between Ti and Si(100) surface.

Pt - Al Ga N ∕ Ga N Schottky diodes operated at 800°C for hydrogen sensing

Schottky diodes on AlGaN∕GaN heterostructures with Pt catalytic metal are fabricated and characterized from 200to800°C for H2 sensing. Over this large range of temperature, the forward current of Schottky diodes increases with exposure to H2 gas, which is attributed to the reduction of Schottky barrier heights resulting from hydrogen absorption in the catalytic metal. The results indicate that AlGaN∕GaN heterostructure Schottky diodes are capable of high-temperature operation for H2 sensing up to 800°C. As temperature increases, the hydrogen detection sensitivity of Pt–AlGaN∕GaN Schottky diodes improves due to the more effective H2 dissociation. When the testing ambient is changed from N2 to 5% H2/95% N2, the value of the Schottky barrier height decreases by 11 and 120meV at 200 and 800°C, respectively.

AlGaN/GaN Schottky diode hydrogen sensor performance at high temperatures with different catalytic metals

Schottky diodes on AlGaN/GaN heterostructures with Pt, IrPt, and PdAg catalytic metals are fabricated and characterized from 200 °C to 800 °C for H 2 sensing. Over this large range of temperature, the forward current of all the diodes increases with exposure to H 2 gas, which is attributed to Schottky barrier height reduction caused by the atomic hydrogen absorption on the metal–oxide interface. The results indicate that AlGaN/GaN heterostructure Schottky diodes are capable of high-temperature H 2 sensor operation up to 800 °C. As temperature increases, the hydrogen detection sensitivity of Pt and IrPt diodes improves due to the more effective H 2 dissociation. However, the sensitivity of PdAg diodes degrades with the increase of temperature due to thermal instability of PdAg. At a range of temperature from 200 °C to 300 °C, PdAg diodes exhibit significant higher sensitivity compared with Pt and IrPt diodes. IrPt and Pt diodes show higher sensitivity at temperatures above 400 °C.

Voltage dependence of effective barrier height reduction in inhomogeneous Schottky diodes

The Schottky barrier height (SBH) variation and its dependence on applied voltage for NiSi/n-Si Schottky diodes with different SBH inhomogeneities have been studied by temperature-dependent current–voltage technique. The results show that the effective barrier height is strongly dependent on the SBH inhomogeneity and the applied voltage. The reduction of effective barrier height increases as the bias varies from forward to reverse, indicating that the pinch off, or more precisely saying, the presence of saddle point in the depletion region, does strongly affect the current transport. Under low reverse bias, the SBH reduction is proportional to one-fourth power of the band bending, which indicates that strip-like SBH inhomogeneity rather than patch-like SBH inhomogeneity exists in our samples. The strip region parameter ω is determined to be 1.63 × 10 −3 and 3.21 × 10 −3 V −1/2 cm −1/2 for the two diodes respectively. Under high reverse bias, the SBH reduction shows different behaviours for diodes with different SBH inhomogeneity. For diodes with small inhomogeneity, the SBH reduction increases faster than the one-fourth power of the band bending while for diodes with large inhomogeneity, the reduction increases more slowly than in the low reverse bias region. The reason is also explained in term of pinch off.