Modulation of Junction Modes in SnSe2/MoTe2 Broken-Gap van der Waals Heterostructure for Multifunctional Devices.

We study the electronic and optoelectronic properties of a broken-gap heterojunction composed of SnSe2 and MoTe2 with gate-controlled junction modes. Owing to the interband tunneling current, our device can act as an Esaki diode and a backward diode with a peak-to-valley current ratio approaching 5.7 at room temperature. Furthermore, under an 811 nm laser irradiation the heterostructure exhibits a photodetectivity of up to 7.5 × 1012 Jones. In addition, to harness the electrostatic gate bias, Voc can be tuned from negative to positive by switching from the accumulation mode to the depletion mode of the heterojunction. Additionally, a photovoltaic effect with a fill factor exceeding 41% was observed, which highlights the significant potential for optoelectronic applications. This study not only demonstrates high-performance multifunctional optoelectronics based on the SnSe2/MoTe2 heterostructure but also provides a comprehensive understanding of broken-band alignment and its applications.

Quasi-2D Halide Perovskite Memory Device Formed by Acid-Base Binary Ligand Solution Composed of Oleylamine and Oleic Acid.

Organometal halide perovskite materials are receiving significant attention for the fabrication of resistive-switching memory devices based on their high stability, low power consumption, rapid switching, and high ON/OFF ratios. In this study, we synthesized 3D FAPbBr3 and quasi-2D (RNH3)2(FA)1Pb2Br7 films using an acid-base binary ligand solution composed of oleylamine (OlAm) and oleic acid in toluene. The quasi-2D (RNH3)2(FA)1Pb2Br7 films were synthesized by controlling the protonated OlAm (RNH3+) solution concentration to replace FA+ cations with large organic RNH3+ cations from 3D FAPbBr3 perovskites. The quasi-2D (RNH3)2(FA)1Pb2Br7 devices exhibited nonvolatile write-once read-many (WORM) memory characteristics, whereas the 3D FAPbBr3 only exhibited hysteresis behavior. Analysis of the 3D FAPbBr3 device indicated operation in the trap-limited space-charge-limited current region. In contrast, quasi-2D (RNH3)2(FA)1Pb2Br7 devices provide low trap density that is completely filled by injected charge carriers and then subsequently form conductive filaments (CFs) to operate as WORM devices. Nanoscale morphology analysis and an associated current mapping study based on conductive atomic force microscopy measurements revealed that perovskite grain boundaries serve as major channels for high current, which may be correlated with the conductive low-resistive-switching behavior and formation of CFs in WORM devices.

Fabrication of pyramidal (111) MAPbBr3 film with low surface defect density using homogeneous quantum-dot seeds.

Nucleation and seeding of organometal halide perovskite (OHP) films have been extensively investigated for forming high-density, large-crystalline, and low-defect films. In this study, CH3NH3PbBr3 (MAPbBr3) films with a low defect density are synthesized via a molecular exchange mechanism using MAPbBr3 quantum dots as seeds. The synthesized films exhibit a pyramidal morphology with a (111) crystal plane. The distribution of the (111) plane is controlled by adjusting the seed concentration. The pyramidal MAPbBr3 films exhibit improved photoluminescence intensity and uniformity compared with films produced using seedless toluene. When the seeds are employed, the surface trap density is reduced by a factor of 3.5, suppressing the photocurrent hysteresis and nonsaturated response of photodetectors. Additionally, the films formed using the seeds have improved stability owing to the chain decomposition reaction induced by electron beam heating.