Applications of two-dimensional tungsten disulfide and boron nitride nanosheets in self-powered photodetectors and memory devices

Abstract

Since single-layer graphene was isolated from highly-oriented pyrolytic graphite in 2004, it led to the beginning of a new revolution in materials science due to its many applications in nano-electronic device technology. Two-dimensional (2D) materials have attracted the most attention for capacitive energy storage applications. Amongst these most interesting studies, the most predominant has been on their atomic structures, mechanical, optical, electronic, thermal, and intrinsic and extrinsic defects, which serve as the basis for a variety of promising technologies.<br /> <br /> The recent progress in 2D materials is tungsten disulfide (WS₂) nanosheets, which are considered the most prominent member of the transition metal dichalcogenides (TMDs) family due to their outstanding optical and electronic properties in creating ultraviolet- and visible-light-sensitive photodetectors. This material exhibits a unique electronic band structure that is characterized by its broadband spectral response, excellent light absorption, sensitivity to interlayer interactions, ultra-fast bleach recovery time, and tunable bandgaps ranging from 1.3 to 2.05 eV according to the layer structure. Additionally, they also present particularly interesting properties owing to their high charge carrier mobility and high switching speed. The bulk composition of WS₂ characterized by energy-dispersive X-ray analysis showed an S/W ratio of 1.70. After mechanical exfoliation and fabrication of WS₂ thin film on SiO₂/Si substrates using the spin-coating technique, the S/W ratio was from about 1.2 to 1.34, which indicated certain deficiencies in the S atoms. This structure of the nanosheets seems to be highly efficient in photoelectric conversion, given that they reached responsivity of 0.12 and 12.74 mA/W at 670 nm under bias voltages of 0 and 2 V, with intensities of 5.2 and 4.1 mW/cm², respectively. The highest detectivity was 1.17 &times; 10¹⁰ cm Hz^1/2, which is an acceptable value for low-bias photodetectors. In our study, we demonstrated that 2D WS₂ nanosheets exhibit high photon absorption in a wide range of spectra from the near-infrared (IR) to near-UV spectrum.<br /> <br /> Instead, Two-dimensional hexagonal boron nitride nanosheets (BNNSs), one of the most widely studied 2D layered materials, have an electronic structure similar to that of graphene and are used to boost the mechanical, electrical, thermal, and optical properties of nanomaterials. The potential application of BNNSs in 2D electronics is limited because their insulating nature does not participate in charge carrier transport. In our research, carbon-doped 2D BNNS was obtained through a CO₂-pulsed laser deposition (CO₂-PLD) technique on silicon dioxide (SiO₂) and molybdenum (Mo) substrates to minimize the band gap and form a thin film with semiconductor electrical properties, thus enhancement of O₂ adsorption. The results also showed hysteresis stable over a wide range of temperatures, which makes them a promising candidate for materials based on non-volatile memory devices. Due to its functional properties and its relation to the resistive switching phenomenon, this innovative material with n-type electronic properties could improve device performance and data retention. In this sense constitutes a good alternative to design two series of Schottky barrier models with Au/BNNS/Au lateral and Au/BNNS/Mo vertical structures. Thus, the addition of carbon to BNNSs creates boron vacancies, which exhibit partially ionic character because of the electron pairs in sp² hybridized B-N and weak van der Waals forces, which also helps to enhance its electrical properties at the metal- BNNS-metal interface.