Tungsten telluride (WTe2) is a transition group metal chalcogenide compound with a layered structure. In its orthogonal unit cell, the tungsten chain is distributed one-dimensionally along the a-axis direction of the tellurium layer, and it is a non-magnetic semimetal material.
Researchers at the Ulsan National Institute of Science and Technology (UNIST) in South Korea recently introduced a method for producing thin and patterned transition metal ditelluride thin films that can be integrated into two-dimensional metal semiconductors. Their synthesis technology was published in a paper in "Nature Electronics", which can solve the problems associated with the high contact resistance of existing electronic devices based on two-dimensional materials.
Since the discovery of graphene, other two-dimensional layered materials with similar characteristics have attracted widespread attention. These materials include transition metal tungsten ditelluride and molybdenum ditelluride (WTe2 and MoTe2) and other transition metal tellurides.
These transition metal ditellurides are a class of transition metal chalcogenides that have unique and extraordinary electrical and optical properties. They show great hope for the development of various technologies such as quantum technology, transistors and phase-change memory.
"Most of the studies using 2-D transition metal ditelluride are made exclusively from mechanically exfoliated flakes in bulk single crystals, which hinders the practical application of materials," Soon, one of the researchers who conducted this study -Professor Yong Kwon said, "Besides, interface defects between metals and semiconductors will trigger contact problems, which usually reduces the carrier injection efficiency of nanoelectronic devices based on two-dimensional materials. We tried to solve the problem of using low work function. The metal 2-D transition metal ditelluride solves these contact problems. "
The new method designed by Professor Song-Yong Kwon and colleagues to synthesize transition metal ditelluride requires the use of tellurium-rich eutectic alloys as the gas source to trigger crystal nuclei and crystal growth. Using this method, the researchers were able to grow 4-inch scale 2-D transition metal ditelluride at a relatively low temperature of 450 ° C for a short period of time (about 10 minutes). It is worth noting that this process can also be adjusted to create wafer-level films with a variety of different structural patterns.
Seunguk Song, one of the researchers in this study, said: "We use 2-D transition metal ditelluride films as electrical contacts to inject carriers into 2-D semiconductors, such as molybdenum disulfide. We found This electronic device follows the ideal carrier injection law and has a significant advantage in controlling the efficiency of the electron flow at the interface. "
Professor Kwon, Song and colleagues used thin films synthesized using their method to establish electrical contacts and integrate them into existing 2D semiconductors. It is found that the resulting device is superior to other devices based on similar 2-D metal materials, showing lower contact resistance and higher performance.
"The key to our production method is to continuously provide a large amount of tellurium vapour to the transition metal precursor to promote their chemical reaction," Song said. "This is particularly important because the chemical activity between W and Te is very low, and it is often difficult to grow successfully. To alleviate this problem, the precursor of NixTey alloy film was selected as the source of Te."
In the thin film synthesized by the researchers, because NixTey is in a liquid state and the growth temperature is higher than the melting point of the alloy (also known as the eutectic point), the compound NixTey continuously provides and captures Te vapour. This process ultimately avoids the scarcity of Te, which is often observed during powder-based chemical vapour deposition.
Professor Kwon said: "By transferring 2D MoS2 crystals to 2D patterned (W, Mo) Te2 thin films, we can simply fabricate heterogeneous structures in vertical contact. Since there are no interface problems, these 2-D height of the 2-D metal-semiconductor transistor is adjustable, depending on the work function of (W, Mo) Te2. This allows us to obtain the lowest barrier, other reports use 3-D, or In the study of 2-D metal contacts, the height of transistors based on single-layer MoS2 has also decreased. "
This research may have important significance for the future development of electronic products based on two-dimensional materials. Most notably, the synthesis method proposed by Professor Song and his colleagues can open up the possibility of controlling certain types of polarity in two-dimensional semiconductors by producing new two-dimensional metals with different work functions.
Song said: "In nature, there are other various 2D metals with interesting physical properties, but their high quality and large area growth are still very few. Based on the synthesis of these new 2D metals, we now plan to study 2D / 2D heterostructure and device integration. "
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