Optoelectronic diode based on p-n junction is one of the most fundamental device building blocks with extensive applications. Compared with graphene, layered transition-metal dichalcogenides demonstrate promising applications in novel valley-electronics and opto-electronics. Here we reported the fabrication and optoelectronic properties of a single multilayer MoS 2 sheet. Our results indicate that the thin MoS 2 shows linear transport property while thick MoS 2 shows diode characteristic with well-defined current rectification behavior. We assign that the rectification behavior is due to the formation of p-n junction in the single multilayer MoS 2 piece. The intrinsic defects in MoS 2 can change the conduction polarity. Such as: sulfur vacancies contribute to the n-type behavior while sulfur interstitials and molybdenum vacancies contribute to the p-type conduction. The variation of intrinsic defect and stoichiometry is obvious over the micrometer range in thick MoS 2 . The fabricated MoS 2 transistors were assessed under bias and gate voltage modulation with exposed to red, green and UV light at vacuum. The multilayer MoS 2 shows dominant p-type behavior under dark condition while shows dominant n-type conduction under light illumination. In addition, this MoS 2 phototransistor shows evident photovoltaic effect. The open-circuit voltage (V oc ) and short-circuit current (I sc ) are observed to be -0.48 V and 494 nA under red illumination. These results demonstrate the potential application of single multilayer MoS 2 sheet in optoelectronics, such as light-emitting diodes (LEDs), field-effect photovoltaic cells and photodetectors.
Layered two-dimensional (2D) gallium monochalcogenide (GaX, X ¼ S, Se, Te) semiconductor crystals hold great promise for potential electronics and photonics application. In this paper, we reported the optoelectronic properties of 2D bandgap engineered GaSe 0.5 Te 0.5 nanoflakes. The GaSe 0.5 Te 0.5 nanoflakes were synthesized by chemical vapor deposition (CVD) and characterized by XRD, SEM, TEM, XPS, Raman and PL spectra, which demonstrate the high crystal quality of as-prepared nanoflakes. The photodetector based on single GaSe 0.5 Te 0.5 nanoflake shows fast response time, high reversibility and stability both in air and vacuum. The photo-responsivity is up to 22 A W À1 under illumination of 532 nm light. More interesting, the GaSe 0.5 Te 0.5 nanoflake photodetector demonstrate extended light response range, as compared with pure GaSe. The photo-responsivity is 13 A W À1 for 650 nm red light. The present results suggest strongly that the bandgap engineered 2D GaSe 0.5 Te 0.5 nanoflakes hold extensive applications in next-generation photodetection and photosensing nanodevices.
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