ACS Nano (2019)

Integrating two-dimensional (2D) materials with organic molecules into hybrid hererostructures is far less common than fabricating conventional van der Waals stacks. However, this combination may provide an attractive strategy for making devices with a functionality tailored through molecular design. Now, Y. Zhao et al. demonstrate a generic approach for designing optically switchable field-effect transistors (FETs), based on photochromic molecules physisorbed on 2D semiconductors.

To fabricate hybrid heterostructures, alkoxy-substituted (AZO) molecules are selectively deposited onto a patterned channel area comprising either MoS2 or black phosphorus (BP). Then, to reduce interfacial trap density and improve the photoresponse speed of the optoelectronic devices, the researchers introduce the trap-free polymer benzocyclobutene. The reversible light-induced doping/undoping of the 2D FET channel occurs via the tuning of the population ratio of trans-/cis-AZO molecules, resulting in the observation of several conductance states in the MoS2 FET and the long retention time of the metastable cis-AZO — exceeding 15 hours. Finally, using the reversible isomerization property of AZO, Zhao and colleagues successfully created ambipolar BP FETs as well as lateral light-tunable p–n diodes.