NTC DL: 2D materials-based nanotransistors

#2D #materials #nanotechnology #device #physics #microelectronic #sscs

Two-dimensional materials hold great promise for future nanoelectronics. Their atomic thickness enables highly scaled field-effect transistors with reduced short-channel effects and relatively high carrier mobility.  In this presentation, the electrical and optical properties of 2D transition metal
dichalcogenides (TMDs such as MoS 2 , WSe 2 , ReSe 2 , PtSe 2 , and PdSe 2 ), GeAs, and black phosphorus are discussed.

The intrinsic electrical transport properties of 2D materials are commonly investigated using back-gated field-effect transistors, due to the low density of process-induced defects and the easy fabrication. Electrical transport, modulation of the conductivity by a back-gate, effect of electron irradiation, environmental pressure and surface adsorbates, and photoresponse are investigated in TMD nanosheets obtained by either mechanical exfoliation or chemical vapor deposition on SiO 2 /Si substrates.

It is shown that the contact resistance can be tuned by electron irradiation, which reduces the Schottky barrier and improves the 2D material/metal contact.  It is demonstrated that adsorbates can change the polarity of the charge carriers and enhance the hysteresis in the transfer characteristics of TMD-based field-effect transistors. It is reported that several 2D materials exhibit strong photoresponse due to their direct bandgap and density of states that favour the interaction with light. Time-resolved photocurrent measurements demonstrate that many 2D based devices exhibit slow or persistent photoresponse that is attributed to intrinsic or extrinsic trap states, photobolometric effect and desorption of adsorbates. It is highlighted how positive and negative photoconductivity can coexist in the same 2D-based device, the dominance of one type over the other being controlled by O 2 and H 2 O adsorbates. The strong dependence of the channel conductance on electrical stress, air pressure, gas type, and light make 2D materials-based devices suitable for memory, gas, and light sensing applications. Finally, as the tunable conductivity and the sharp-edge geometry facilitate the extraction of electrons under the application of an electric field, it is proved that several 2D materials are also effective field emitters and that their emission current can be modulated by a back-gate.