2D Semiconductor for Future Electronics

2D semiconductors or van der Waals solids are attracting interest of many research groups around the globe as they promise stable chemical, electrical and mechanical behavior for designing of electronic devices of future. 2D semiconductor is natural occurring semiconductor material with atomic scale thickness, this single atomic layer material could prove to be a boon for improved engineering applications. The most common 2D semiconductor material is Graphene which is having single sheet of carbon atoms arranged in a honeycomb lattice as shown in Figure1 (b). In fact Graphene was the first 2D semiconductor material reported in 2004. Recent class of 2D semiconductor materials is TMD (transition metal dichalcogenides) where an atomic level thickness of transition metal layer is sandwiched between two chalcogen atoms layers.

Figure1: Single and multilayer crystalline structures [Google images]

It is found by many research groups that when two different 2D materials are integrated in electronic device, then additional crystal quality and fascinating peroperties can be achieved. These materials have high mobilty of charge carriers at room temperature etc. For example Graphene is a type of material having zero energy gap between its valence and conduction band but sizable natural energy band gaps can be achieved by selecting suitable doping material for Graphene. Advancements in 2D materials have enabled researchers to deposit layered materials that are only one or few unit-cells in thickness to construct sharp in-plane and out-of-plane interfaces between different materials. And the junctions which are formed between these dissimilar materials are called heterojunctions. These heterojunction devices could be used in the design of extremely thin transistors with high electron mobility. Figure below shows the finished electronic gadgets made using heterojunction devices discussed above. These gadgets are flexible, transparent and would be used in applications of future like wearable electronics etc.

Figure2: Flexible and transparent smart electronics devices [5]

Moore's law says that the number of transistors count per chip doubles every 18-24 months, but modern semiconductor technology works on more than Moore's integration. This is owing to rapidly changing technology and some ground breaking findings in material sciences like discovery of 2D semiconductor material. Flow chart in Figure 3 indicates a currently used semiconductor materials along with the future predictions for designing of digital and analog devices. As can be seen quite clearly that 2D material is going to be one of the key constituents for future electronics technology.

Figure 3: Future prospectives of 2-D materials for Analog and Digital circuits [5]

Figure 4 is showing a three terminals structure of Flexible Graphene FETs (Field Effect Transistor). These types of single layered transistors have good light absorption and light emitting property as we explore optoelectronic devices, RF applications etc.

Figure 4: Flexible Graphene based Field Effect Transistor [5]

Since 2011 multiple new 2D materials have been proposed like MoS₂ (molybdenum-sulphide), h-BN (Hexagonal Boron Nitride), black phosphorus etc. all of which could be used for future electronics. The recent research is focused on the development of Graphene based nanodevices like photodetectors and sensors. 2D material based technology would provide promising solutions for the printable and low power electronics. The application of this technology is also expected to extend to the field of photovoltaic, optocouplers and many advanced sensors.

By: Ms. Harpreet Kaur - Asst. Prof. ECE, Chitkara University, H.P.

References

1. http://physicsworld.com/cws/article/news/2014/may/21/hybrid-technology-developed-for-2d-electronics
2. http://iopscience.iop.org/journal/2053-1583/page/Focus-on-Flexible-2D-Electronics
3. https://nrl.ece.ucsb.edu/sites/default/files/sites/default/papers/ESSDERC-2013-Keynote_KB.pdf
4. https://www.sciencedaily.com/releases/2017/09/170918161531.htm
5. https://www.nist.gov/sites/default/files/documents/pml/div683/conference/schwierz.pdf