Fast, Multi‐Bit, and Vis‐Infrared Broadband Nonvolatile Optoelectronic Memory with MoS₂/2D‐Perovskite Van der Waals Heterojunction

Abstract

It has broad application prospects in the fields of biomimetic artificial visual perception and neuromorphic computing. 2D van der Walls (vdW) materials are considered as one of the most potential materials for constructing the NVOM due to their unique light-matter interaction at atomic scale, highly tunable band gap, and diversified electronic structure. [1][2][3][4] In recent years, there have been extensive researches on the development of NVOM in the visible range. [5,6] Light in the near infrared (NIR) range has strong penetrability and the NIR spectra of object carries a variety of characteristic information. NVOM responsive to NIR range will offer unique optical environment adaptability in night, foggy, or another complex environment with accurate recognition, which are strongly required in applications of robots, autonomous driving, and unmanned aerial vehicles. [7,8] Furthermore, the widely used band for optical communication and computing, for example 1550 nm, lies in the NIR region, and the corresponding NVOM is the vital device in optoelectronic integrated chips for neuromorphic computing. [9] However, the responsive range of 2D NVOM is still limited to the visible range.The most common structure for 2D vdW NVOM is the floating gate (FG) structure as shown in Figure 1a, in which, charges are stored in the floating gate because of the isolation Nonvolatile optoelectronic memory (NVOM) integrating the functions of optical sensing and long-term memory can efficiently process and store a large amount of visual scene information, which has become the core requirement of multiple intelligence scenarios. However, realizing NVOM with vis-infrared broadband response is still challenging. Herein, the room temperature vis-infrared broadband NVOM based on few-layer MoS 2 /2D Ruddlesden-Popper perovskite (2D-RPP) van der Waals heterojunction is realized. It is found that the 2D-RPP converts the initial n-type MoS 2 into p-type and facilitates hole transfer between them. Furthermore, the 2D-RPP rich in interband states serves as an effective electron trapping layer as well as broadband photoresponsive layer. As a result, the dielectric-free MoS 2 /2D-RPP heterojunction enables the charge to transfer quickly under external field, which enables a large memory window (104 V), fast write speed of 20 µs, and optical programmable characteristics from visible light (405 nm) to telecommunication wavelengths (i.e., 1550 nm) at room temperature. Trapezoidal optical programming can produce up to 100 recognizable states (>6 bits), with operating energy as low as 5.1 pJ per optical program. These results provide a route to realize fast, low power, multi-bit optoelectronic memory from visible to the infrared wavelength.

Defect and Donor Manipulated Highly Efficient Electron–Hole Separation in a 3D Nanoporous Schottky Heterojunction

“…As for V S -ZIS/N-npG (Figure c), the planar-averaged charge density difference along the Z axis is given in Figure d to intuitively display the variation of the charge density. The designed interfacial charge rearrangement including increased local electron density at V S -ZIS and electron depletion at N-npG corroborates the intense interaction and the regulation of interfacial electronic structure . Notably, the increased accumulated electrons observed on the S vacancy position provides further evidence for the sulfur vacancies serving as electrons traps.…”

Polarized Tunneling Transistor for Ultrafast Memory

“…Work function differences (Δ W ) on the MoS 2 /Trap surface are denoted as ΔW T‑M . As shown in Figure f–h, Δ W T‑M = 409 meV at V g = −10 V results in a positive potential energy gradient for MoS 2 /Trap heterostructure, which releases electrons from the trap layer to MoS 2 (erase operation); while Δ W T‑M = −348 meV at V g = 10 V results in a negative potential energy gradient for MoS 2 /Trap heterostructure, which attracts the electrons to trap layer from MoS 2 (program operation). − The trap layer can function similarly to the floating gate layer in a floating gate transistor (Supplementary Note 1).…”

Memory Window Ratio Enhancement of p-Type WSe2 Memtransistors Using Dielectric GeSe2 Nanosheets with Asymmetric Interfaces for Neuromorphic Computing

“…For instance, the van der Waals (vdW) stack interface is used as a charge-trapping site where traps behave in a nonvolatile manner in type I − vdW heterostructures (vdWHs) with 2D WBGSs. Surface vacancies in Ruddlesden–Popper perovskite (2D-RPP) serve as effective electron trapping sites in the dielectric-free MoS 2 /2D-RPP heterojunction memtransistor . Interface defects in Ge 4 Se 9 play a key role as a charge trap layer in inducing hysteresis behavior .…”

“…Surface vacancies in Ruddlesden−Popper perovskite (2D-RPP) serve as effective electron trapping sites in the dielectric-free MoS 2 /2D-RPP heterojunction memtransistor. 26 Interface defects in Ge 4 Se 9 play a key role as a charge trap layer in inducing hysteresis behavior. 27 However, 2D materials include two surfaces, i.e., one side can be functionalized for charge trapping and the other can suppress carrier scattering from the channel−dielectric interface, thereby obtaining high-field-effect mobility.…”