Recent technology development of logic devices based on 2-D semiconductors such as MoS2, WS2, and WSe2 has triggered great excitement, paving the way to practical applications. Making low-resistance p-type contacts to 2-D semiconductors remains a critical challenge. The key to addressing this challenge is to find high-work function metallic materials which also introduce minimal metal-induced gap states (MIGSs) at the metal/semiconductor interface. In this work, we perform a systematic computational screening of novel metallic materials and their heterojunctions with monolayer WSe2 based on ab initio density functional theory and quantum device simulations. Two contact strategies, van der Waals (vdW) metallic contact and bulk semimetallic contact, are identified as promising solutions to achieving Schottky-barrier-free and low-contact-resistance p-type contacts for WSe2 p-type field-effect transistor (pFETs). Good candidates of p-type contact materials are found based on our screening criteria, including 1H-NbS2, 1H-TaS2, and 1T-TiS2 in the vdW metal category, as well as Co3Sn2S2 and TaP in the bulk semimetal category. Simulations of these new p-type contact materials suggest reduced MIGS, less Fermi-level pinning effect, negligible Schottky barrier height and small contact resistance (down to 20 Ωμm )
more »
« less
A back-to-back diode model applied to van der Waals Schottky diodes
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 barrier
- Award ID(s):
- 2047509
- PAR ID:
- 10532134
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- Journal of Physics: Condensed Matter
- Volume:
- 36
- Issue:
- 45
- ISSN:
- 0953-8984
- Format(s):
- Medium: X Size: Article No. 455301
- Size(s):
- Article No. 455301
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
more » « less
Abstract A simple room‐temperature process of depositing MXene on a III‐V structure with embedded 2D electron gas (2DEG) is used, which results in a large area, , photodetector (PD) device that greatly outperforms vacuum deposited Ti/Au metal‐semiconductor‐metal (MSM) PD's. By co‐optimizing properties of 2D MXene contacts and the III‐V material heterojunctions, this device sets new operating records with responsivity up to 1.04 A W‐1at low optical powers, corresponding to >230% internal quantum efficiency, dark current of 50 , >105.6‐dB dynamic range, and 25–150 ps response time, which improves the previous MXene‐Semiconductor‐MXene responsivity by >2.7 times and is 7 × 103–−106times faster compared to other MXene‐based PDs. This is achieved by enhancing the Schottky barrier height by forming a Van der Waals (vdW) heterojunction between a wide bandgap AlGaAs surface layer and spin coated
Ti 3C 2T z electrodes. A layered architecture transports the optically generated electrons to a 2DEG channel at the GaAs/AlGaAs heterointerface, where they are rapidly collected. The landscaped electric field pushes the slow holes to an underlying low temperature‐grown GaAs (LT‐GaAs) region where they recombine. The proposed Schottky‐2DEG Photoconductor‐Schottky model for device operation shows how this device circumvents the canonical limitations of gain‐bandwidth product, and carrier transit time, while replacing the need for vacuum deposition of gold or other precious metals. -
more » « less
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
Abstract Metal–semiconductor interfaces, known as Schottky junctions, have long been hindered by defects and impurities. Such imperfections dominate the electrical characteristics of the junction by pinning the metal Fermi energy. Here, a graphene–WSe2p‐type Schottky junction, which exhibits a lack of Fermi level pinning, is studied. The Schottky junction displays near‐ideal diode characteristics with large gate tunability and small leakage currents. Using a gate electrostatically coupled to the WSe2channel to tune the Schottky barrier height, the Schottky–Mott limit is probed in a single device. As a special manifestation of the tunable Schottky barrier, a diode with a dynamically controlled ideality factor is demonstrated.
-
more » « less
An analysis of the optoelectronic properties and photocurrent generation mechanisms in 2D multilayer crystallites of black phosphorus (BP) is conducted from 350 K down to cryogenic temperatures
T of ≈6 K using a broad‐band white light source, and the results are compared to another semiconducting van der Waals solid, MoS2. Both the BP and MoS2devices are contacted with Mo at the bottom as the electrode metal. The Mo–BP interface yields a low Schottky barrier ≈ −28.3 meV and a high photoresponsivityR of ≈2.43 × 105 A W−1at a source‐drain bias voltage of ≈0.5 V (300 K, and incident optical power ≈3.16 μW cm−2). This article is the first to highlight the empirical use of Mo as a contact metal with BP. The highR is attributed to the low at the interfaces, in conjunction with the large effective area of a bottom contact architecture that increases the collection of photoexcited carriers and reduces thermal dissipation into the substrate from the largely suspended 2D nanodiaphragm. The results show the promise of BP to potentially advance thermoelectric and optoelectronic devices stemming from this monoelemental, direct bandgap 2D van der Waals solid.
