Fabrication of heterojunction between 2D molybdenum disulfide (MoS2) and gallium nitride (GaN) and its photodetection properties have been reported in the present work. Surface potential mapping at the MoS2/GaN heterojunction is done using Kelvin Probe Force Microscopy to measure the conduction band offset. Current-voltage measurements show a diode like behavior of the heterojunction. The origin of diode like behavior is attributed to unique type II band alignment of the heterojunction. The photocurrent, photoresponsivity and detectivity of the heterojunction are found to be dependent on power density of the light. Photoresponse investigations reveal that the heterojunction is highly sensitive to 405 nm laser with very high responsivity up to 105 A/W. The heterojunction also shows very high detectivity of the order of 1014 Jones. Moreover, the device shows photoresponse in UV region also. These observations suggest that MoS2/GaN heterojunction can have great potential for photodetection applications.

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We made a report on the fabrication and characterization of a mechanically exfoliated multilayered gallium selenide-based metal–semiconductor–metal (MSM) photodetector using Ti/Au as metal contacts. A significant increase in photocurrent was observed when the photodetector was illuminated with a 380 nm laser, giving the photoresponsivity, external quantum efficiency, and detectivity of 2.6 A/W, 850%, and 1.0 × 1012 Jones, respectively, at a power density of 0.35 mW/cm2 at room temperature. Experimentally, it was observed that the device shows high photoresponse in both UV and visible regions. The performance of this GaSe-based photodetector was also checked at various temperatures, ranging from room temperature to 120 °C. It was found that the detector was thermally stable, giving a maximum photoresponsivity of 4.5 A/W at 120 °C.

Despite the noteworthy progress made in the nanotubular architectures with well-de ned lengths and diameter, the synthesis of a purely covalent bonded organic nanotube, so far, proved to be elusive. Our work includes a hitherto unavailable structure, "Covalent Organic Nanotubes (CONTs)," to the repertoire. Strong covalent bonds between C, N, and O imparts high thermal and chemical stability of CONTs. This novel bottom-up approach provides an edge over the carbon nanotubes (CNTs) in functionalization, synthetic conditions, and porosity. CONT-1 exhibits a BET surface area of 321 m2g-1. These exible CONTs intertwine with each other. The computational studies establish the role of solvent as the critical driving force for this type of convolution. Upon ultrasonication, the intertwined CONT-1 coil to form the toroidal superstructure.

Control over thickness, size, and area of chemical vapor deposition (CVD) grown molybdenum disulfide (MoS2) flakes is crucial for device application. Herein, we report a quantitative comparison of CVD synthesis of MoS2 on SiO2/Si substrate using three different precursors viz., molybdenum trioxide (MoO3), ammonium heptamolybdate (AHM), and tellurium (Te). A threestep chemical reaction mechanism of evolution of MoS2 from MoO3 micro-crystals is proposed for MoO3 precursor. Furthermore, a strategy based on growth temperature and ratio of amount of precursors is developed to systematically control thickness and area of MoS2 flakes. Our findings show that for large-sized crystalline monolayer MoS2 flakes, MoO3 is a better choice than AHM and Te-assisted synthesis. Moreover, Te as growth promoter, can lower down growth temperature by 250C. This study can be further used to fabricate MoS2 based high-performance electronic devices such as photodetectors, thin film transistors, and sensors.

Photoresponse characteristics of monolayer MoS 2 based metal-semiconductor-metal devices using high work function metal palladium have been investigated. The Pd-MoS 2 based MSM device shows a very low dark current of the order of pA. The device exhibits significant current enhancement after illumination with the responsivity of 0.8 A W −1 at power density of 2 mW cm −2 for 650 nm laser. The linear dependence of photocurrent with power density reveals that the trap states have much less effect on the performance of the fabricated device. Responsivity was observed to enhance with the increasing power density of incident laser. The optoelectronic performance of the fabricated device was examined by current measurement at higher operating temperatures up to 120 °C and photo to dark current ratio showed decrement with the increase in temperature.

Mixed-dimensional heterostructures have shown their potential in electronic devices. However, their functionality is limited by a complete understanding of the contacts and the current transport behavior. Here, we explore the electrical properties of the P-n heterojunction diode fabricated using p-type gallium nitride and layered molybdenum disulfide. The resulting P-n diode is rectifying in nature with current rectification of three orders of magnitude. The careful choice of Ohmic contacts on both the semiconductors reveals distinctly rectifying behavior of the heterojunction diode. The as-fabricated diode is tested at various temperatures, and the conduction mechanism in the device is analyzed based on the temperature dependent electrical characterizations. In addition, photoresponse characterization reveals that the P-n heterojunction is highly sensitive to a 405 nm laser with a high responsivity of 444 A/W at a reverse bias voltage of 5 V and shows photovoltaic behavior. The heterojunction diode acts as a self-powered photodetector. Our findings show the potential of the MoS2/GaN heterojunction in highly efficient photodetector applications.

While 2D materials have been investigated for their potential applications in nanoelectronic and optoelectronic devices, their functionality is still not fully explored due to lack of proper understanding of metal contacts on these materials. The present work pertains to the study of electrical behavior of different metals such as chromium, silver, nickel, and platinum deposited on to exfoliated MoS 2 flakes. Comparative study of different metal contacts to MoS 2 shows that Ag/Au exhibits good ohmic behavior with high current injection efficiency and better linearity and symmetry of I-V curves than Cr/ Au and Ni/Au contacts. Specific contact resistivity is measured to be 4.54 Â 10 À4 Ω cm 2 using transmission line measurement (TLM) for Ag/MoS 2 contacts. Further, taking Ag/Au as ohmic contact, Pt/MoS 2 Schottky barrier diode is fabricated with a high rectification ratio of about 900. Barrier height and ideality factor of 0.56 eV and 2.1, respectively are obtained. This study opens up the possibility of having high quality metal contacts on MoS 2 with potential applications in nanoscale devices.