Ultrahigh Gauge Factor in Graphene/MoS₂ Heterojunction Field Effect Transistor with Variable Schottky Barrier

Lee, Ilmin,Kang, Won Tae,Shin, Yong Seon,Kim, Young Rae,Won, Ui Yeon,Kim, Kunnyun,Duong, Dinh Loc,Lee, Kiyoung,Heo, Jinseong,Lee, Young Hee,Yu, Woo Jong American Chemical Society 2019 ACS NANO Vol.13 No.7

<P>Piezoelectricity of transition metal dichalcogenides (TMDs) under mechanical strain has been theoretically and experimentally studied. Powerful strain sensors using Schottky barrier variation in TMD/metal junctions as a result of the strain-induced lattice distortion and associated ion-charge polarization were demonstrated. However, the nearly fixed work function of metal electrodes limits the variation range of a Schottky barrier. We demonstrate a highly sensitive strain sensor using a variable Schottky barrier in a MoS<SUB>2</SUB>/graphene heterostructure field effect transistor (FET). The low density of states near the Dirac point in graphene allows large modulation of the graphene Fermi level and corresponding Schottky barrier in a MoS<SUB>2</SUB>/graphene junction by strain-induced polarized charges of MoS<SUB>2</SUB>. Our theoretical simulations and temperature-dependent electrical measurements show that the Schottky barrier change is maximized by placing the Fermi level of the graphene at the charge neutral (Dirac) point by applying gate voltage. As a result, the maximum Schottky barrier change (ΔΦ<SUB>SB</SUB>) and corresponding current change ratio under 0.17% strain reach 118 meV and 978, respectively, resulting in an ultrahigh gauge factor of 575 294, which is approximately 500 times higher than that of metal/TMD junction strain sensors (1160) and 140 times higher than the conventional strain sensors (4036). The ultrahigh sensitivity of graphene/MoS<SUB>2</SUB> heterostructure FETs can be developed for next-generation electronic and mechanical-electronic devices.</P> [FIG OMISSION]</BR>

Inhomogeneity of barrier heights of transparent Ag/ITO Schottky contacts on <i>n</i>-type GaN annealed at different temperatures

Yoon, Su-Jung,Lee, Jeeyun,Seong, Tae-Yeon Elsevier 2018 Journal of alloys and compounds Vol.742 No.-

<P><B>Abstract</B></P> <P>We report on the formation of high barrier-height and transparent Ag/ITO Schottky contacts on <I>n</I>-GaN (<I>n</I> <SUB> <I>d</I> </SUB> = 5 × 10<SUP>18</SUP> cm<SUP>−3</SUP>) for optoelectronic and transparent electronic devices. Calculations using the thermionic emission model-based current-voltage characteristics of the samples annealed at various temperatures showed small Schottky barrier heights (SBHs) of 0.31–0.37 eV and ideality factors of 1.84–2.19. Conventional activation energy plot showed greatly smaller Richardson constant than the theoretical value. To understand such abnormality, the modified Richardson plot, a model of lateral SBH variation with Gaussian distribution, and capacitance-voltage method were used, where their SBHs were estimated to be in the range 0.74–0.93 eV. Together with the temperature-dependent SBHs and ideality factors, these results imply that SBH behavior could be explained in terms of barrier inhomogeneity at the interfaces. The Ag/ITO samples annealed at 500 °C transmitted 80.9% at 560 nm. The X-ray photoemission spectroscopy (XPS) Ga 2<I>p</I> core level spectra from the interfaces of the samples shifted toward either higher or lower energies. Scanning transmission electron microscopy (STEM)-energy dispersive X-ray spectroscopy mapping results revealed the outdiffusion of Ga atoms from <I>n</I>-GaN when annealed at 500 °C. Based on the electrical, XPS and STEM results, the annealing temperature dependence of the SBHs is described and discussed.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Transparent and high barrier-height Ag/ITO Schottky contacts on <I>n</I>-GaN were developed. </LI> <LI> Barrier heights are evaluated with Modified Richardson plot, inhomogeneity model and C-V method. </LI> <LI> Ag/ITO contacts show a Schottky barrier height of 0.92 eV when annealed at 500 °C. </LI> <LI> Ag/ITO samples show a transmittance of ∼81% at 560 nm when annealed at 500 °C. </LI> <LI> •Outdiffusion of N and Ga atoms was found to be responsible for different SBH behavior. </LI> </UL> </P>

Device characteristics of Schottky barrier diodes using In-Ga-Zn-O semiconductor thin films with different atomic ratios

Kim, Jae-Won,Jung, Tae-Jun,Yoon, Sung-Min Elsevier 2019 Journal of alloys and compounds Vol.771 No.-

<P><B>Abstract</B></P> <P>Oxide semiconductor Schottky barrier diodes (SBDs) were fabricated by using amorphous In-Ga-Zn-O (IGZO) semiconducting thin films with different atomic ratios. Higher rectification ratios and Schottky barrier heights (SBHs) were obtained when the oxygen partial pressure was high during the sputtering deposition of the IGZO films. The increase in Ga composition effectively enhanced the device characteristics, including the rectification ratio and the SBH of the SBDs. These properties were closely related to the control of oxygen vacancy concentration within the IGZO and the resulting conduction behaviors owing to Fermi-level pinning and tunneling current through the Schottky barrier. The fabricated SBD using IGZO with a higher Ga composition (In:Ga:Zn = 1.0:0.8:0.3) exhibited a rectification ratio of 8.3 × 10<SUP>6</SUP> and an SBH of 0.79 eV.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We fabricated Schottky barrier diodes using In-Ga-Zn-O oxide semiconductors. </LI> <LI> Effects of oxygen partial pressures (PO<SUB>2</SUB>) and film compositions were investigated. </LI> <LI> PO<SUB>2</SUB> conditions during the sputtering has marked impacts on device characteristics. </LI> <LI> Increase in Ga composition is effective for enhancing the diode performance. </LI> <LI> Less amount of oxygen vacancies within the IGZO is preferred for the diodes. </LI> </UL> </P>

Fabrication of 1.2 kV Ni/4H-SiC Junction Barrier-Controlled Schottky Diodes with a Single P+ Ion-Implantation Process

주성재,강인호,방욱,김상철,김남균 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.5

This paper presents the fabrication details and the characterization results of 4H-SiC junction barrier-controlled Schottky (JBS) diodes whose forward- and reverse-bias characteristics were optimized by using a single p+ ion implantation process. Ni was used for both Schottky and ohmic electrode formation and aluminum was implanted with multiple energies to form JBS grids and field-limiting rings (FLRs) simultaneously. The blocking voltage increased with decreasing FLR spacing and increasing doping concentration and a maximum wafer-level blocking voltage of 1500 V was obtained at an optimal doping concentration of 5× 1018/cm3 and an optimal FLR spacing of 3μm. The on-resistance increased with decreasing JBS grid spacing, but the correlation was not outstanding and devices having FLRs and JBS grids with the above structural parameters were proven to have the most balanced forward and reverse characteristics. Packaged JBS diodes whose voltage and current ratings of 1.2 kV and 8 A were successfully demonstrated and specific on-resistances were ~3 mΩ·cm2 at current densities of 130 ~ 560 A/cm2. Schottky barrier height (SBH) was ~1.7 eV. The reverse leakage current density was about 1μA/cm2 at 1200 V. A linear I-V relationship was maintained even at the highest current density of 800 A/cm2. The reverse-recovery time (trr) was 8.8 ns and the reverse-recovery charge (Qrr) was 2.3 nC at a dI/dt of 167 A/μs. This paper presents the fabrication details and the characterization results of 4H-SiC junction barrier-controlled Schottky (JBS) diodes whose forward- and reverse-bias characteristics were optimized by using a single p+ ion implantation process. Ni was used for both Schottky and ohmic electrode formation and aluminum was implanted with multiple energies to form JBS grids and field-limiting rings (FLRs) simultaneously. The blocking voltage increased with decreasing FLR spacing and increasing doping concentration and a maximum wafer-level blocking voltage of 1500 V was obtained at an optimal doping concentration of 5× 1018/cm3 and an optimal FLR spacing of 3μm. The on-resistance increased with decreasing JBS grid spacing, but the correlation was not outstanding and devices having FLRs and JBS grids with the above structural parameters were proven to have the most balanced forward and reverse characteristics. Packaged JBS diodes whose voltage and current ratings of 1.2 kV and 8 A were successfully demonstrated and specific on-resistances were ~3 mΩ·cm2 at current densities of 130 ~ 560 A/cm2. Schottky barrier height (SBH) was ~1.7 eV. The reverse leakage current density was about 1μA/cm2 at 1200 V. A linear I-V relationship was maintained even at the highest current density of 800 A/cm2. The reverse-recovery time (trr) was 8.8 ns and the reverse-recovery charge (Qrr) was 2.3 nC at a dI/dt of 167 A/μs.

Association of alkyl chain length in the Electrolytes with the Photovoltaic Properties

진호철,정미진,이준호,( Sabrina Aufar Salma ),( Ratna Dewi Maduwu ),손동환,김주현 한국공업화학회 2019 한국공업화학회 연구논문 초록집 Vol.2019 No.1

It is a requirement for high-performance bulk-heterojunction organic solar cells to investigate the interfacial effect on photogenerated holes and electrons transfer. As it is known, the smooth transfer can be achieved by decreasing the Schottky barrier. Herein, we investigated the association of alkyl chain length in the electrolytes, 1,1'-bis(1-alkyl)-4,4′-bipyridine-1,1′-diium benzenesulfonate (V-butyl-2OTs, V-hexyl-2OTs, and V-dodecyl-2OTs). The power conversion efficiencies (PCEs) and the Schottky barrier of the electrolytes were calculated to 8.1%/0.37, 8.3%/0.30, and 8.6%/0.23, respectively, where the Schottky barrier was induced from the difference between acceptor material’s LUMO and electrode. The obvious correlation was found between the PCE and the Schottky barrier. The photogenerated current density which well-matched with the decreasing of the Schottky barrier by the interfacial dipole from the electrolytes become the main reason of the enhancement of the PCEs.

New Method to Determine the Schottky Barrier in Few-Layer Black Phosphorus Metal Contacts

Lee, Su Yeong,Yun, Won Seok,Lee, J. D. American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.8

<P>Schottky barrier height and carrier polarity are seminal concepts for a practical device application of the interface between semiconductor and metal electrode. Investigation of those concepts is usually made by a conventional method such as the Schottky-Mott rule, incorporating the metal work function and semiconductor electron affinity, or the Fermi level pinning effect, resulting from the metal-induced gap states. Both manners are, however, basically applied to the bulk semiconductor metal contacts. To explore few-layer black phosphorus metal contacts far from the realm of bulk, we propose a new method to determine the Schottky barrier by scrutinizing the layer-by-layer phosphorus electronic structure from the first-principles calculation combined with the state-of-the-art band unfolding technique. In this study, using the new method, we calculate the Schottky barrier height and determine the contact polarity of Ti, Sc, and Al metal contacts to few-layer (mono-, bi-, tri-, and quadlayer) black phosphorus. This gives a significant physical insight toward the. utmost layer-by-layer manipulation of electronic properties of few-layer semiconductor metal contacts.</P>

Characteristics of Schottky-barrier Source/Drain Metal-oxide-polycrystalline Thin-film Transistors on Glass Substrates

Seung-Min Jung,조원주,정종완 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.1

Polycrystalline-silicon (poly-Si) Schottky-barrier thin-film transistors (SB-TFTs) with Ptsilicided source/drain junctions were fabricated on glass substrates, and the electrical characteristics were examined. The amorphous silicon films on glass substrates were converted into high-quality poly-Si by using excimer laser annealing (ELA) and solid phase crystallization (SPC) methods. The crystallinity of poly-Si was analyzed by using scanning electron microscopy, transmission electron microscopy, and X-ray diffraction analysis. The silicidation process was optimized by measuring the electrical characteristics of the Pt-silicided Schottky diodes. The performances of Pt-silicided SB-TFTs using poly-Si films on glass substrates and crystallized by using ELA and SPC were demonstrated. The SB-TFTs using the ELA poly-Si film demonstrated better electrical performances such as higher mobility (22.4 cm2/Vs) and on/off current ratio (3 × 106) and lower subthreshold swing value (120 mV/dec) than the SPC poly-Si films. Polycrystalline-silicon (poly-Si) Schottky-barrier thin-film transistors (SB-TFTs) with Ptsilicided source/drain junctions were fabricated on glass substrates, and the electrical characteristics were examined. The amorphous silicon films on glass substrates were converted into high-quality poly-Si by using excimer laser annealing (ELA) and solid phase crystallization (SPC) methods. The crystallinity of poly-Si was analyzed by using scanning electron microscopy, transmission electron microscopy, and X-ray diffraction analysis. The silicidation process was optimized by measuring the electrical characteristics of the Pt-silicided Schottky diodes. The performances of Pt-silicided SB-TFTs using poly-Si films on glass substrates and crystallized by using ELA and SPC were demonstrated. The SB-TFTs using the ELA poly-Si film demonstrated better electrical performances such as higher mobility (22.4 cm2/Vs) and on/off current ratio (3 × 106) and lower subthreshold swing value (120 mV/dec) than the SPC poly-Si films.

p-type Conduction in ZnO Nanowire Schottky Field-effect Transistors with Pt Metal Electrodes

Du-Won Jeong,김주진,이정오 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.5

To obtain p-type conduction in a ZnO nanowire, field effect transistors were fabricated from a short ZnO nanowire with Pt contact electrodes. Since Pt metal has a high work function and is chemically inert, the Fermi level can align with the valence band side of the ZnO nanowire in such a way as to produce a high Schottky barrier. The current-voltage characteristics showed a non-linear behavior due to the high Schottky barrier between the ZnO nanowire and the Pt, and the gate transfer curves exhibited a weak p-type conduction behavior. To further enhance the hole conduction in the ZnO nanowire channel, we exposed the devices to F_2 gas, which is effective at capturing electrons. The F_2 adsorbed onto the ZnO FET and improved the hole conduction behavior relative to that of the intrinsic ZnO FET. A p-type gate response was obtained in the high source-drain bias voltage region.

Effect of different dielectrics on performance of sub-5.1 nm blue phosphorus Schottky barrier field-effect transistor from quantum transport simulation

Chen Wen,Jing Sicheng,Wang Yu,Pan Jinghua,Li Wei,Bian Baoan,Liao Bin 한국물리학회 2022 Current Applied Physics Vol.43 No.-

Two-dimensional materials have attracted great attention because of their ultra-thin atomic layer thickness and high carrier mobility. In this work, we investigated the electronic transport of in-plane (IP) heterojunction based on Cu/Blue Phosphorus (BlueP), and the results suggest the metallization at the IP Cu/BlueP contact interface and a small Schottky barrier. Then, we investigated the performance of 5.1 nm IP BlueP Schottky barrier field-effect transistors (SBFET) with different dielectrics (SiO2, Al2O3, Y2O3, and La2O3) using quantum transport simulations. The results show that IP BlueP SBFETs with four dielectrics satisfy the off-state requirement of the International Technology Roadmap for Semiconductors (ITRS) for the high-performance (HP) device. However, the on-state current of only IP BlueP SBFET with La2O3 satisfies the requirements of ITRS. This will provide a reference for designing BlueP SBFETs.

Enhanced High-Temperature Electrical Resistivity of Aluminum Nitride Obtained by Engineering a Schottky Barrier at Grain Boundaries

Lee Eunsil,Pee Jae-Hwan,Lee Sung-Min,Kim Jong-Young,Shim Wooyoung 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.77 No.8

An enhanced high- temperature electrical resistivity of AlN at high voltage was obtained by using MgO doping to modulate the Schottky barrier. Doped MgO was precipitated in an ~100-nm-thick layer near grain boundaries, which reduced not only anionic carriers, but also the carrier mobility, due to the formation of defects (Mg´Al, O·N). According to an impedance analysis, the activation energy and the resistivity due to grain boundaries were increased by MgO doping, suggesting an elevated Schottky barrier. As a result, a remarkable high-voltage electrical resistivity, which is greater than 1010 Ω·cm at 550 °C/100 V, can be achieved, which is valuable for electrostatic chucking devices.