Dispositivos de memória em heteroestruturas 2D de MoSe2 sobre clinocloro

Abstract

The study of materials that present lamellar characteristics and can be isolated in monolayers has become relevant due to their unique properties widely reported in the literature. The transition metal dichalcogenides (TMDs), semiconductors members of the lamellar materials' group, raise interest in the fabrication of devices through the so-called van der Waals heterostructures (vdWHs). This stems from the fact that TMD's monolayers are susceptible to local defects, charge exchange with the substrate, and substrate roughness, and are generally encapsulated by atomically-flat and insulating materials, such as hexagonal boron nitride (hBN). Due to the factors mentioned, the photoluminescence (PL) emissions, intense in TMDs, can be modulated by external factors, such as electric and magnetic fields and some specific properties of the substrates. Considering the need to miniaturize the devices, and the need to expand the list of appropriate insulators for the vdWHs, which is limited so far, this work aimed to characterize the effects of a clinochlore's substrate, a lamellar phyllosilicate, in the optical responses of a device containing a molybdenum diselenide (MoSe2) monolayer coated with a layer of hBN. For this purpose, optoelectronic studies were carried out at cryogenic temperatures as a function of an external electric field and variable changes such as bias sweep rate (time) and excitation power to the sample. Optical emissions compatible with excitons and trions were observed, which showed to be highly modulated with the applied voltage. The obtained curves assumed a hysteretic shape, stable in time, and independent of factors such as polarization and the initial direction of the applied electric field. In addition, temporal measurements revealed the existence of transients in different scales, which indicates memory effects related to the charge dynamics and fluctuations in carrier population and polarization of the material. In particular, the observed phenomena are directly related to the presence of the clinochlore, since such responses were not noted in a sample containing a hBN-encapsulated TMD. Therefore, from the results obtained, it was possible to prove the so-called mem-emitters, i.e., light-emitting devices that present memory effects to external stimuli, whose existence has recently been reported.