RESUMEN
Van der Waals junctions hold significant potentials for various applications in multifunctional and low-power electronics and optoelectronics. The multistep device fabrication process usually introduces lattice mismatch and defects at the junction interfaces, which deteriorate device performance. Here the layer engineering synthesis of van der Waals homojunctions consisting of 2H-MoTe2 with asymmetric thickness to eliminate heterogenous interfaces and thus obtain clean interfaces is reported. Experimental results confirm that the homostructure nature gives rise to the formation of pristine van der Waals junctions, avoiding chemical disorders and defects. The ability to tune the energy bands of 2H-MoTe2 continuously through layer engineering enables the creation of adjustable built-in electric field at the homojunction boundaries, which leads to the achievement of self-powered photodetection based on the obtained 2H-MoTe2 films. Furthermore, the successful integration of 2H-MoTe2 homojunctions into an image sensor with 10 × 10 pixels, brings about zero-power consumption and near-infrared imaging functions. The pristine van der Waals homojunctions and effective integration strategies shed new insights into the development of large-scale application for two-dimensional materials in advanced electronics and optoelectronics.
RESUMEN
Point defects dictate various physical, chemical, and optoelectronic properties of two-dimensional (2D) materials, and therefore, a rudimentary understanding of the formation and spatial distribution of point defects is a key to advancement in 2D material-based nanotechnology. In this work, we performed the demonstration to directly probe the point defects in 2H-MoTe2 monolayers that are tactically exposed to (i) 200 °C-vacuum-annealing and (ii) 532 nm-laser-illumination; and accordingly, we utilize a deep learning algorithm to classify and quantify the generated point defects. We discovered that tellurium-related defects are mainly generated in both 2H-MoTe2 samples; but interestingly, 200 °C-vacuum-annealing and 532 nm-laser-illumination modulate a strong n-type and strong p-type 2H-MoTe2, respectively. While 200 °C-vacuum-annealing generates tellurium vacancies or tellurium adatoms, 532 nm-laser-illumination prompts oxygen atoms to be adsorbed/chemisorbed at tellurium vacancies, giving rise to the p-type characteristic. This work significantly advances the current understanding of point defect engineering in 2H-MoTe2 monolayers and other 2D materials, which is critical for developing nanoscale devices with desired functionality.
RESUMEN
In recent years, two-dimensional (2D) nonlayered Bi2O2Se-based electronics and optoelectronics have drawn enormous attention owing to their high electron mobility, facile synthetic process, stability to the atmosphere, and moderate narrow band gaps. However, 2D Bi2O2Se-based photodetectors typically present large dark current, relatively slow response speed, and persistent photoconductivity effect, limiting further improvement in fast-response imaging sensors and low-consumption broadband detection. Herein, a Bi2O2Se/2H-MoTe2 van der Waals (vdWs) heterostructure obtained from the chemical vapor deposition (CVD) approach and vertical stacking is reported. The proposed type-II staggered band alignment desirable for suppression of dark current and separation of photoinduced carriers is confirmed by density functional theory (DFT) calculations, accompanied by strong interlayer coupling and efficient built-in potential at the junction. Consequently, a stable visible (405 nm) to near-infrared (1310 nm) response capability, a self-driven prominent responsivity (R) of 1.24 A·W-1, and a high specific detectivity (D*) of 3.73 × 1011 Jones under 405 nm are achieved. In particular, R, D*, fill factor, and photoelectrical conversion efficiency (PCE) can be enhanced to 4.96 A·W-1, 3.84 × 1012 Jones, 0.52, and 7.21% at Vg = -60 V through a large band offset originated from the n+-p junction. It is suggested that the present vdWs heterostructure is a promising candidate for logical integrated circuits, image sensors, and low-power consumption detection.
RESUMEN
The intrinsically nonmagnetic feature of van der Waals (vdW) layered transition-metal dichalcogenide (TMDC) semiconductors limits the spintronic applications of these semiconductors. In this paper, we demonstrate a facile Te flux strategy to induce intrinsic ferromagnetism in the vdW layered 2H-MoTe2 semiconductor by magnetic chromium (Cr) doping. The Curie temperature (Tc) and saturation magnetization (Ms) can be well tuned by adjusting the Cr doping concentration. A notable Tc up to 275 K can be achieved for the vdW layered Cr-doped 2H-MoTe2 bulk crystals, which is much higher than that of recently reported van der Waals ferromagnetic semiconductors (Tc is mostly less than 70 K), in contrast to the diamagnetic feature of the pristine MoTe2. Meanwhile, the highest Ms of the vdW layered Cr-doped 2H-MoTe2 bulk crystals can reach 4.78 emu g-1, which is stronger than most values reported for magnetic-element-doped van der Waals materials. In addition, all of the as-grown semiconducting Cr-doped 2H-MoTe2 (Cr-2H-MoTe2) single crystals display a large magnetic anisotropy with an out-of-plane easy axis of magnetization. The observed ferromagnetism in the Cr-2H-MoTe2 has intrinsic characteristics, which can be mainly attributed to the spin polarization caused by Cr doping as confirmed by the density functional theory (DFT) calculations. Our approach offers an avenue to tune the ferromagnetism in the vdW layered semiconductor and explore its diverse spintronic and magnetoelectric applications.