An official website of the United States government
Abstract Reducing the Schottky barrier height and Fermi level de‐pinning in metal‐organic semiconductor contacts are crucial for enhancing the performance of organic transistors. The reduction of the Schottky barrier height in bottom‐contact top‐gate organic transistors is demonstrated by adding 1 nm thick atomic layer deposited Al2O3on the source and drain contacts. By using two different donor‐acceptor copolymers, bothp‐andn‐type transistors are investigated. Temperature‐dependent current–voltage measurements from non‐treated, self‐assembled monolayer treated, and Al2O3treated Au source‐drain contact field‐effect transistors with varying channel lengths are carried out. The drain current versus drain voltage near zero gate voltage, which may be described by the thermionic emission model at temperatures above 150 K, allows the estimation of the Schottky barrier height (φB). The Al2O3contact‐treated transistors show more than 40% lowerφBcompared with the non‐treated contacts in thep‐type transistor. Similarly, an isoindigo‐based transistor, withn‐type transport, shows a reduction inφBwith Al2O3treated contacts suggesting that such ultrathin oxide layers provide a universal method for reducing the barrier height.
more »
« less
Diode‐Like Selective Enhancement of Carrier Transport through Metal–Semiconductor Interface Decorated by Monolayer Boron Nitride
Abstract 2D semiconductors such as monolayer molybdenum disulfide (MoS2) are promising material candidates for next‐generation nanoelectronics. However, there are fundamental challenges related to their metal–semiconductor (MS) contacts, which limit the performance potential for practical device applications. In this work, 2D monolayer hexagonal boron nitride (h‐BN) is exploited as an ultrathin decorating layer to form a metal–insulator–semiconductor (MIS) contact, and an innovative device architecture is designed as a platform to reveal a novel diode‐like selective enhancement of the carrier transport through the MIS contact. The contact resistance is significantly reduced when the electrons are transported from the semiconductor to the metal, but is barely affected when the electrons are transported oppositely. A concept of carrier collection barrier is proposed to interpret this intriguing phenomenon as well as a negative Schottky barrier height obtained from temperature‐dependent measurements, and the critical role of the collection barrier at the drain end is shown for the overall transistor performance.
more »
« less
- Award ID(s):
- 1944095
- PAR ID:
- 10456806
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Materials
- Volume:
- 32
- Issue:
- 36
- ISSN:
- 0935-9648
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract This paper provides comprehensive experimental analysis relating to improvements in the two-dimensional (2D) p-type metal–oxide–semiconductor (PMOS) field effect transistors (FETs) by pure van der Waals (vdW) contacts on few-layer tungsten diselenide (WSe2) with high-k metal gate (HKMG) stacks. Our analysis shows that standard metallization techniques (e.g., e-beam evaporation at moderate pressure ~ 10–5 torr) results in significant Fermi-level pinning, but Schottky barrier heights (SBH) remain small (< 100 meV) when using high work function metals (e.g., Pt or Pd). Temperature-dependent analysis uncovers a more dominant contribution to contact resistance from the channel access region and confirms significant improvement through less damaging metallization techniques (i.e., reduced scattering) combined with strongly scaled HKMG stacks (enhanced carrier density). A clean contact/channel interface is achieved through high-vacuum evaporation and temperature-controlled stepped deposition providing large improvements in contact resistance. Our study reports low contact resistance of 5.7 kΩ-µm, with on-state currents of ~ 97 µA/µm and subthreshold swing of ~ 140 mV/dec in FETs with channel lengths of 400 nm. Furthermore, theoretical analysis using a Landauer transport ballistic model for WSe2SB-FETs elucidates the prospects of nanoscale 2D PMOS FETs indicating high-performance (excellent on-state current vs subthreshold swing benchmarks) towards the ultimate CMOS scaling limit.more » « less
-
null (Ed.)High contact resistance is one of the primary concerns for electronic device applications of two-dimensional (2D) layered semiconductors. Here, we explore the enhanced carrier transport through metal–semiconductor interfaces in WS 2 field effect transistors (FETs) by introducing a typical transition metal, Cu, with two different doping strategies: (i) a “generalized” Cu doping by using randomly distributed Cu atoms along the channel and (ii) a “localized” Cu doping by adapting an ultrathin Cu layer at the metal–semiconductor interface. Compared to the pristine WS 2 FETs, both the generalized Cu atomic dopant and localized Cu contact decoration can provide a Schottky-to-Ohmic contact transition owing to the reduced contact resistances by 1–3 orders of magnitude, and consequently elevate electron mobilities by 5–7 times. Our work demonstrates that the introduction of transition metal can be an efficient and reliable technique to enhance the carrier transport and device performance in 2D TMD FETs.more » « less
-
Internal photoemission or hot-electron injection (HEJ) occurring at the metal-semiconductor (MS) Schottky interface has shown great promise in sub-bandgap photodetection and photovoltaics. In this paper, we put forward a plasmonic metagrating-interlayer-semiconductor (PMIS) structure that can significantly enhance the photon-to-electron conversion efficiency of HEJ-based optoelectronic devices. Thanks to the effect of image force-induced barrier lowering, a metal-interlayer-semiconductor (MIS) heterojunction with an ultrathin 2D material interlayer can considerably facilitate the hot electron transport across the Schottky barrier, resulting in a high internal quantum efficiency (IQE). Meanwhile, nanopatterning the MIS heterojunction into the plasmonic metagrating enables high optical absorption such that the device’s external quantum efficiency (EQE) can be nearly equal to its IQE. In addition, this device can be wavelength- and polarization-selective by tailoring the geometry and dimensions of plasmonic metagrating, thereby paving a promising path toward bandgap-independent photodetection, energy harvesting, and photocatalysis.more » « less
-
Abstract The use of metal and semimetal van der Waals contacts for 2D semiconducting devices has led to remarkable device optimizations. In comparison with conventional thin-film metal deposition, a reduction in Fermi level pinning at the contact interface for van der Waals contacts results in, generally, lower contact resistances and higher mobilities. Van der Waals contacts also lead to Schottky barriers that follow the Schottky–Mott rule, allowing barrier estimates on material properties alone. In this study, we present a double Schottky barrier model and apply it to a barrier tunable all van der Waals transistor. In a molybdenum disulfide (MoS2) transistor with graphene and few-layer graphene contacts, we find that the model can be applied to extract Schottky barrier heights that agree with the Schottky–Mott rule from simple two-terminal current–voltage measurements at room temperature. Furthermore, we show tunability of the Schottky barrierin-situusing a regional contact gate. Our results highlight the utility of a basic back-to-back diode model in extracting device characteristics in all van der Waals transistors.more » « less
