Hole Barrier Height Research Articles

Influence of Incorporating Rare Earth Metals on the Schottky Barrier Height of Ni Silicide

Characterized herein is a different physical mechanism for the formation of Ni silicide by incorporating rare earth (RE) metals such as ytterbium (Yb), erbium (Er), and dysprosium (Dy). Although the incorporation of any RE metal increases the Schottky barrier height (SBH) for holes in Ni silicide due to the formation of a ternary phase silicide, Yb induced the greatest increase in SBH because, unlike the other metals, Yb atoms accumulated at the silicide/silicon interface.

Flexible Single-Crystalline Ge p-Channel Thin-Film Transistors With Schottky-Barrier Source/Drain on Polyimide Substrates

Single-crystalline Ge p-channel thin-film transistors with Schottky-barrier source/drain (S/D) on flexible polyimide substrates are fabricated by a simple low-temperature process ( ? 250°C), which preserves the high mobility of Ge channel. Adhesive wafer bonding and Smart-Cut techniques were utilized to transfer the single-crystalline Ge thin film onto polyimide substrates. The Schottky-barrier S/D is formed by using Pt/n-Ge contact, showing a low hole barrier height. The device has a linear hole mobility of ~ 170 cm2·V-1·s-1 and a saturation current of ~ 1.6 ?A/?m at Vd = - 1.5 V for the channel length and width of 15 and 280 ?m, respectively.

Advanced Source/Drain Engineering for MOSFETs: Schottky Barrier Height Tuning for Contact Resistance Reduction

Contact resistance is becoming an important limiting factor for achieving high MOSFET drive current and speed in future technology nodes. In this paper, we review the technology solutions for reducing the contact resistance between a metal silicide contact and the source/drain region. Several new approaches for decreasing the electron and hole barrier heights between the source/drain region and the silicide layer in n-FET and p-FET, respectively, will be examined. Integration of these approaches in advanced device architectures will be discussed.

Fermi level depinning at the germanium Schottky interface through sulfur passivation

We demonstrate the depinning of Fermi level on both p- and n-type germanium after sulfur passivation by aqueous (NH4)2S treatment. Schottky contacts realized using metals with a wide range of work functions produce nearly ideal behavior confirming that the Fermi level is depinned. Examination of the passivated surface using x-ray photoelectron spectroscopy reveals bonding between Ge and sulfur. It is shown that good Ohmic contacts to n-type Ge and a hole barrier height (ϕBp) of 0.6 eV to p-type Ge can be achieved after this passivation treatment, with Zr Schottky contacts. This is the highest ϕBp reported so far.

Tuning of the Schottky barrier height in NiGe/n-Ge using ion-implantation after germanidation technique

In this paper, a method of ion-implantation after germanidation (IAG) has been presented to modulate the Schottky barrier (SB) heights on germanium substrates. Schottky diodes have been fabricated with improved rectifying current curves and larger Ion/Ioff ratio up to 106. A relatively high effective electron barrier height for NiGe/n-Ge has been achieved by the BF2+ IAG technique, which suggests a record-low effective hole barrier height of nearly 0.06 eV. The tuning of SB height can be mainly contributed to the effects of fluorine. In addition, there is a process temperature window between 350 to 450 °C for the drive-in annealing of IAG to obtain optimized SB heights. These results provide the design guidelines for the process integration of germanium based Schottky barrier source/drain metal-oxide-semiconductor field-effect transistors.

Morphologies, structures, and interfacial electronic structure of perylene on Au(111)

Various coverages of perylene thin films on Au(111) were investigated using scanning tunneling microscopy (STM) and ultraviolet photoelectron spectroscopy and x-ray photoelectron spectroscopy. A Schottky junction formed between Au(111) and perylene consisted of a large 0.65 eV interface dipole and a hole barrier height of 0.85 eV. A wetting layer of approximately 4 Å thickness was initially formed followed by island formation, consistent with Stranski–Krastanov growth. Room temperature STM investigations of nominal one monolayer perylene films revealed symmetry equivalent domains and two different stable commensurate lattice structures. Perylene film growth mode, film structure and the energy level diagram are discussed.

Energy-band alignment of Al2O3 and HfAlO gate dielectrics deposited by atomic layer deposition on 4H–SiC

Energy band alignment and band gap of Al2O3 and HfAlO films grown by atomic layer deposition on 4H–SiC were determined using x-ray photoelectron spectroscopy. Al2O3 exhibited a symmetric band profile with a conduction band offset (ΔEC) of 1.88 eV and a valence band offset (ΔEV) of 1.87 eV. HfAlO yielded a smaller ΔEC of 1.16 eV and ΔEV of 1.59 eV. The higher dielectric constant and higher effective breakdown field of HfAlO compared to Al2O3, coupled with sufficient electron and hole barrier heights, makes it a potential dielectric for use on 4H–SiC, and provokes interest in further investigation of HfAlO/4H–SiC properties.

Schottky Barrier Height of Nickel Silicide Contacts Formed on $\hbox{Si}_{1 - x}\hbox{C}_{x}$ Epitaxial Layers

Embedded Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1 -</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> C <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> source/drain junctions are currently considered to achieve electron mobility enhancement in nMOSFETs by inducing uniaxial tensile strain in the channel region. To utilize the mobility advantage of this technology, it is imperative to form low-resistivity contacts to Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1 -</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> C <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> alloys. In this letter, the electron and hole barrier heights at the NiSi/Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1 -</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> C <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> interface were measured up to a carbon concentration of 1.2%. The results indicate that the NiSi Fermi level moves away from the valence-band edge with increasing carbon concentration such that the hole barrier height increases by 68 meV in spite of the upward movement of the valence band. Within the same carbon concentration range, the electron barrier height decreases by as much as 170 meV, which is significant considering the exponential dependence of contact resistivity on barrier height.

Fermi-level pinning at the interface between metals and nitrogen-doped Ge2Sb2Te5 examined by x-ray photoelectron spectroscopy

The metal/α-Ge2Sb2Te5 interface was examined using x-ray photoelectron spectroscopy. Doping Ge2Sb2Te5 with nitrogen leads to an increase in hole barrier height at the interface between metals and nitrogen-doped Ge2Sb2Te5. Hole barrier height at metal/α-Ge2Sb2Te5 interface is reduced slightly by increasing the work function of the metal. We observed significant pinning of metal Fermi level toward the valence band energy of undoped or nitrogen-doped Ge2Sb2Te5. This leads to low hole barrier height and good Ohmic contact formed between metals and α-Ge2Sb2Te5.

The Dependence of the Performance of Strained NMOSFETs on Channel Width

The dependence of the performance of strained NMOSFETs on channel width was investigated. When the channel width was varied, the stress in the channel varied accordingly. This changed the electron effective mass and, consequently, the on-state current I on. By shrinking the channel width of a strained NMOSFET from 1 to 0.1 mum and by keeping the channel length at 55 nm, the on-state drain current per unit channel width was enhanced by 22%. The gate leakage current was also affected by the stress in the channel, which can be explained by the increase in hole barrier height at the Si/SiO2 interface. Furthermore, when the film stress was increased by 1 GPa, the gate leakage current density Jg of a strained NMOSFET with a channel width of 0.1 mum and a length of 55 nm under a negative bias -3 V was reduced by 63%.

Schottky Barrier Height of Erbium Silicide on $ \hbox{Si}_{1 - x}\hbox{C}_{x}$

In this letter, the Schottky barrier height of erbium silicide contacts formed on Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> alloys was measured. The alloys were pseudomorphically grown on Si wafers with 0% to 1.2% C occupying the substitutional sites. Schottky barrier diodes were fabricated with an ideality factor of 1.13 or less. The hole barrier height was found to be 0.73 eV independent of the C concentration. This suggests that the electron barrier height should decrease with increasing C concentration due to the reduction in the semiconductor bandgap. For 1.2% C, the electron barrier is estimated to be 0.29 eV.

Platinum Germanosilicide as Source/Drain Contacts in P-Channel Fin Field-Effect Transistors (FinFETs)

In this paper, platinum germanosilicide (PtSiGe) was investigated extensively as an alternative to nickel germanosilicide (NiSiGe) for contact formation on silicon-germanium (SiGe) source/drain (S/D) stressors. We show that PtSiGe has superior thermal and morphological stability as compared to NiSiGe. Our results further show that the formation of PtSiGe yields a low hole barrier height (Phi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</sup> ) of 215 meV in a self-aligned process. We also demonstrated the integration of PtSiGe contacts in FinFET devices. FinFETs with PtSiGe contacts achieve a 27% reduction in external resistance (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">EXT</sub> ) compared to FinFETs with NiSiGe contacts. Statistical comparison reveals that the drive current performance is enhanced by 21% while maintaining comparable control of short-channel effects. These results illustrate the potential of forming contacts with low Schottky barrier heights using PtSiGe in strained transistors with SiGe S/D stressors, thereby reducing R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">EXT</sub> and extending transistor performance.

Role of hybridization on the Schottky barrier height of carbon nanotube field effect transistors

The impact of hybridization on the Schottky barrier height (SBH) for holes at a metal/nanotube contact is investigated using ab initio density-functional theory. For small diameters, the impact of hybridization is a deviation of the SBH in comparison to that calculated using the ``$1/d$'' rule, where $d$ is the diameter of the carbon nanotube (CNT). In the hybridization region, the SBH reduces with chiral angle, suggesting that CNTs in this region may well be suited to microelectronic applications due to small SBH and large band gaps. Hybridization also causes a difference between the effective mass of electrons and holes, supposed to be identical within the tight-binding approximation. A strongly patterned behavior of the effective mass dependent on chirality and diameter is also reported here.

Experimental design for the determination of the injection barrier height at metal/organic interfaces using temperature dependent current-voltage measurements

Determination of the injection barrier height for holes or electrons at metal/organic interfaces is essential to understanding the device physics of organic electronics. Due to the disordered molecular packing of organic semiconductors, careful consideration is required in the design of both the device structure and the experimental measurement technique used to extract the barrier height. We report a methodology for extracting the injection barrier height at metal/organic interfaces from temperature dependent current-voltage measurements. This methodology includes the design of single carrier devices with specific consideration of the intrinsic properties of organic semiconductors, as well as the design of a variable temperature cryostat suited to the measurement of organic electronic device architectures. Experimental results for single carrier hole-only devices using two commonly studied hole transport materials, namely N,N(')-diphenyl-N,N(')-bis-(1-naphthyl)-1-1(')-biphenyl-4,4(')-diamine (alpha-NPD) and 4,4('),4(")-tris(N-3- methylphenyl-N-phenyl-amino)triphenylamine (m-MTDATA) are also presented as examples.

High-Quality Schottky Contacts for Limiting Leakage Currents in Ge-Based Schottky Barrier MOSFETs

Schottky barrier (SB) Ge channel MOSFETs suffer from high drain-body leakage at the required elevated substrate doping concentrations to suppress source-drain leakage. Here, we show that electrodeposited Ni-Ge and NiGe/Ge Schottky diodes on highly doped Ge show low off current, which might make them suitable for SB p-MOSFETs. The Schottky diodes showed rectification of up to five orders of magnitude. At low forward biases, the overlap of the forward current density curves for the as-deposited Ni/n-Ge and NiGe/n-Ge Schottky diodes indicates Fermi-level pinning in the Ge bandgap. The SB height for electrons remains virtually constant at 0.52 eV (indicating a hole barrier height of 0.14 eV) under various annealing temperatures. The series resistance decreases with increasing annealing temperature in agreement with four-point probe measurements indicating the lower specific resistance of NiGe as compared to Ni, which is crucial for high drive current in SB p-MOSFETs. We show by numerical simulation that by incorporating such high-quality Schottky diodes in the source/drain of a Ge channel PMOS, a highly doped substrate could be used to minimize the source-to-drain subthreshold leakage current.

Thermal Immune NiGermanide for High Performance Ge MOSFETs on Ge-on- Si Substrate Utilizing $ \hbox{Ni}_{0.95}\hbox{Pd}_{0.05}$ Alloy

Highly thermally stable Ni germanide technology for high performance germanium metal-oxide-semiconductor field-effect transistors (Ge MOSFETs) is proposed, utilizing Pd incorporation into Ni germanide. The proposed Ni germanide shows not only the improvement of thermal stability but also the reduction of hole barrier height, which can improve the device on-current by reducing the Ni germanide to p+ source/drain contact resistance. The proposed Ni germanide showed a stable sheet resistance of up to 500degC 30-min postgermanidation annealing due to the suppression of agglomeration and oxidation of Ni germanide and the diffusion of Ni and Ge atoms by the incorporated Pd. Therefore, the proposed Ni0.95Pd0.05 alloy could be promising for the high mobility Ge MOSFET applications.

A Photoemission Study of the Morphology and Barrier Heights of the Interface between Chyrsene and Inert Substrates

Chrysene, a two-dimensional (2D) chiral isomer of tetracene, was deposited onto inert metallic (Au(111), Cu(111), Ag(111), and highly oriented pyrolytic graphite (HOPG)) and semiconducting (SnS 2) substrates with hexagonal symmetry. The interface formation was investigated in situ with photoelectron spectroscopy (X-ray photoelectron spectroscopy and UV photoelectron spectroscopy (UPS)). A detailed analysis of core-level and valence band spectra revealed that the barrier height for holes or electrons is independent of the identity and work function of the metal substrate. Metal/chrysene interfaces are therefore an example of pure Fermi level pinning where changes in the interface dipole potential directly offset changes in the metal work function. The results provide evidence that the pinning may result from a hybridization mechanism between metal s states and organic π states. UPS spectra indicate that the 2D structures of the chrysene wetting layer is different for high work function materials (Au(111), SnS2) compared to low work function materials (Ag(111) and HOPG). Stranski−Krastanov growth was observed on all substrates and is in agreement with optical microscope images of thick chrysene films.

High-quality NiGe/Ge diodes for Schottky barrier MOSFETs

Schottky barrier (SB) Ge channel MOSFETs suffer from high drain-body leakage at the required elevated substrate doping concentrations to suppress source–drain leakage. Here, we show that electrodeposited Ni–Ge and NiGe/Ge Schottky diodes on highly doped Ge show low off current, which might make them suitable for SB-MOSFETs. The Schottky diodes showed rectification of up to five orders in magnitude. At low forward biases, the overlap of the forward current density curves for the as-deposited Ni/ n-Ge and NiGe/ n-Ge Schottky diodes indicates Fermi-level pinning in the Ge bandgap. The SB height for electrons remains virtually constant at ∼0.52 eV (indicating a hole barrier height of ∼0.14 eV) under various annealing temperatures. The series resistance decreases with increasing annealing temperature in agreement with four-point probe measurements indicating the lower specific resistance of NiGe as compared with Ni, which is crucial for high drive current in SB-MOSFETs. We show by numerical simulation that by incorporating such high-quality Schottky diodes in the source/drain of a Ge channel PMOS, highly doped substrate could be used to minimize the subthreshold source to drain leakage current.

Built-in Voltage in Alq3 Based Organic Light-Emitting Diodes Incorporating PEDOT:PSS and LiF Layer

Built-in voltage was measured in Alq3 based organic light-emitting diodes incorporating a PEDOT:PSS and LiF layer by using a modulated photocurrent technique at ambient conditions. A device was made with a structure of anode/Alq3/cathode. Either an ITO or an ITO/PEDOT:PSS was used as an anode, and a LiF/Al was used as a cathode. The built-in voltage of the device is determined from a bias voltage-dependent photocurrent. The applied bias voltage when the magnitude of modulated photocurrent is zero corresponds to a built-in voltage. It was found that an incorporation of PEDOT:PSS layer between the ITO and Alq3 increases a built-in voltage by about 0.4 V. This is consistent to a difference of a highest occupied energy states of ITO and PEDOT:PSS. This implies that a use of PEDOT:PSS layer in anode lowers a hole barrier height. With a use of bilayer cathode system LiF/Al, it was found that a built-in voltage increases as the LiF layer thickness increases in the thickness range of 0 ∼ 1 nm. It indicates that a very thin alkaline metal compound LiF lowers an electron barrier height. These results could be related to an improvement of device efficiency brought about by the insertion of PEDOT:PSS and LiF layer.

SONOS-Type Flash Memory Cell With Metal$/\hbox{Al}_{2}\hbox{O}_{3}/ \hbox{SiN}/\hbox{Si}_{3}\hbox{N}_{4}/\hbox{Si}$ Structure for Low-Voltage High-Speed Program/Erase Operation

High-quality Al2O3 and Si3N4 dielectrics synthesized in a molecular/atomic deposition system were developed and adopted as blocking oxide and tunnel dielectric, respectively in a SONOS-type NAND flash memory cell. In particular, the use of trap-free Si3N4 as tunnel dielectric enables low-voltage erase operation due to its low barrier height for holes, and the relatively high-k value of Al2O3 enhances the low-voltage and high-speed program/erase (P/E) operations. We fabricated and investigated NAND flash memory cells with metal/Al2O3/SiN/Si3N4/Si structure. The fabricated cell shows 3.8-V memory window with P/E conditions of +15 V for 100 mus and -10 V for 10 ms. It also shows good endurance up to 10 000 cycles and more than 1.5-V memory window after ten years.