Periodic Reporting for period 1 - STELLAR (multireSponsive hybrid Transition mEtaL dichaLcogenides-bAsed optoelectRonics – A European Fellowship for career development)
Reporting period: 2018-12-01 to 2020-11-30
When Moore’s Law comes to an end, the further development of electronic devices requires exploring new research directions, including the breakthrough of physics limitation to realize ultimate scaling of device dimensions and the enrichment of device functionality to enable diversification. Two-dimensional (2D) materials with atomic level thickness and ultrahigh surface-to-volume ratio show the ability to ultimately scale down the device dimensions and provide a desirable platform to design novel functional devices. Therefore, 2D materials have been regarded as the promising semiconductor materials in next generation electronic devices. In the STELLAR project, we have developed a unique chemical approach to enrich the functionality of 2D optoelectronic devices. The development of novel 2D technology will offer an alternative solution to solve the great challenges in silicon electronics. The overall objectives of this project were to conduct high-quality research in the field of hybrid 2D optoelectronic devices to develop multiresponsive devices which can respond to multiple independent external stimuli. In summary, the STELLAR project provides a guideline to design light-responsive 2D devices and allowed the development of an electrochemically controlled 2D transistor for the first time. These new findings will bring technology revolution in the electronic industry.
In the STELLAR project, we have performed excellent research in the field of hybrid optoelectronic devices based on heterostructures of switchable molecular systems and 2D materials. Switchable molecular systems include photochromic molecules (such as azobenzenes and diarylethenes) and electrochemically switchable molecules (such as ferrocene). In the library of 2D materials, the STELLAR project mainly focused on 2D semiconductors, for example MoS2, WSe2 and black phosphorus. The molecules undergo a reversible switching process upon exposure to external stimuli, i.e. azobenzene molecules switch between two (meta)stable states with markedly different properties under UV/visible light irradiation, resulting in a modification of the macroscopic properties of the adjacent 2D semiconductors. By combining these switchable molecular systems, 2D devices were constructed to respond to multiple external stimuli, including optical and electrochemical signals. These novel functions are embedded in 2D logic devices, which represents an insightful research direction for the development of electronic and optoelectronic devices.
The STELLAR project was focused on multiresponsive hybrid 2D devices, which can independently respond to external stimuli. Although some excellent works based on graphene have been reported to show responsivity, 2D semiconductor devices with logic functions show more fundamental impact on the industry development. In the STELLAR project, a universal approach was explored to realize light-responsive 2D transistors. The persistent photocurrent in 2D materials is minimized via dielectric engineering, which prevents its negative impact on the light responsivity behavior in hybrid 2D devices. An optically controlled p–n junction device was successfully demonstrated to show functional diversity. Furthermore, an electrochemically controlled hybrid 2D transistor was developed for the first time. The device shows superior performance with high carrier mobility, large on/off current ratio, and ultra-steep subthreshold swing. The combination of electrochemical switching and logic function in hybrid 2D devices represents an unprecedented strategy to pave the road towards novel functional devices.