We demonstrate the fabrication of a monolayer graphene/β-Ga 2 O 3 heterostructure and its interesting prospect of producing a suitable Schottky barrier potential for deep-ultraviolet (DUV) responsive photovoltaic device. The transient response behavior shows a faster response time for photovoltaic mode operation of the photodiode. The fast response at a zero bias is due to generation of photocurrent under an internal built-in field in the graphene/Ga 2 O 3 interface without any contribution from the trapped carriers. The fabricated device also shows an excellent photoresponsivity of 6.1 A W À1 with a slower response time at a low reverse bias voltage (À1.5 V). The high photoresponsivity at a bias voltage can be related to carrier multiplication due to carriers trapping/release process. Our findings show that the graphene/β-Ga 2 O 3 heterostructure can be significant for selfpowered/low power consuming DUV detector applications.

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High performance multifunctional electrocatalysts are attracting significant importance for application in energy storage, energy conversion and various other electrochemical reactions. In this prospect, we report on the effective trifunctional electrocatalytic properties of nitrogen (N) doped graphitic carbon nanofibers (CNFs). The CNFs were synthesized on a nichrome (NiCr) foil by chemical vapor deposition (CVD) process. Incorporation of Ni and Cr was observed in the N doped CNFs sample from microscopic and spectroscopic analysis. The metal nanoparticles can be significant in boosting the trifunctional electrocatalytic behavior. The effective oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) activities were obtained for the CNFs sample with relatively good overpotential values. The electron transfer number per O2 molecule calculated from Koutecky‐Levich (K‐L) plot was found to be 2e− for the ORR reaction. The OER activity of the CNFs is comparable to commercially available iridium oxide (IrO2), signifying the effectiveness of the developed catalyst. Our study revealed that N doped CNFs with incorporation of metal particles synthesized on a binary metal substrate can be significant as ORR, OER, HER trifunctional electrocatalyst.

Fabrication of heterojunction with transition metal dichalcogenide (TMDC) layers and convention bulk semiconductor is of great interest for optoelectronic device applications. Herein, the influence of interface in a fabricated molybdenum sulfide (MoS2) and p‐type silicon (Si) heterostructure on bias‐dependent photoresponse is demonstrated. The MoS2 layers deposited on the p‐type Si wafer show a photovoltaic action and a photoresponsivity of 139 mA W−1 at 860 nm wavelength for a bias voltage of −5 V. It is observed that the spectral photoresponse of the device enhanced considerably with an applied bias voltage than that of the photovoltaic mode due to an effective field effect across the heterojunction. The increase in photoresponsivity at a higher wavelength (>600 nm) is significant than that of lower wavelength (<500 nm) at the bias voltage. This may due to surface recombination of photocarriers for higher energy photons in the presence of interface states at the MoS2/Si heterojunction. The understanding of photocarriers behavior in the fabricated MoS2/Si heterojunction interface can be critical to develop high photoresponsive heterojunction devices.

Charge transfer interaction at the interface of semiconducting layered materials is of great interest to develop effective heterojunction optoelectronic devices. Here, we demonstrate the charge transfer interaction and formation of an active heterojunction between the molybdenum disulfide (MoS 2 ) layer and p-type copper iodide (CuI) exhibiting excellent photoresponsive properties. The CuI film was fabricated by solid phase iodization of a copper film and direct thermal evaporation processes, which led to the formation of a transparent conducting layer. The thermally evaporated CuI film showed the main diffraction peak for the (111) plane, confirming the formation of the γ-CuI cubic crystal structure along the (111) plane on the MoS 2 layers. The photoluminescence (PL) quenching effect was observed for the γ-CuI/MoS 2 heterostructure, which can be attributed to the spontaneous separation of charge carriers at the interface. A photoresponsivity of 0.27 A/W was obtained at a bias voltage of 5 V for the γ-CuI/MoS 2 heterojunction device with illumination of monochromatic light. Our finding shows that the excellent photoresponsivity in the fabricated heterojunction is due to the formation of an effective interface between the two materials for efficient exciton dissociation and charge separation.

2D materials such as molybdenum sulfide (MoS2) integrated with conventional semiconductors lead to the fabrication of novel heterojunctions with pivotal electrical and optoelectronic properties. Herein, an approach is reported which addresses the growth of MoS2 crystals on the lattice‐matched Ga–polar gallium nitride (GaN) wafer using ammonium tetrathiomolybdate (ATM) as a precursor in a chemical vapor deposition (CVD) process, instead of using the molybdenum‐oxide‐based precursors. Unidirectional triangular MoS2 crystals and continuous film are obtained on the free‐standing Ga–polar GaN substrate. Further, the interface quality of the as‐synthesized MoS2 crystals and GaN wafer is explored by X‐ray photoelectron spectroscopy. It is observed that a good quality interface can be obtained by using the ammonia‐containing ATM precursor, where the surface oxygen at the interface is significantly less. A heterojunction device is fabricated with the synthesized MoS2 layer on GaN, showing excellent rectifying diode characteristics and a photovoltaic action with light illumination. This study reveals the suitability of the ammonia‐containing ATM precursor for the growth of MoS2 crystals on GaN in the CVD process to obtain a suitable heterostructure for device applications.

Here, the formation of an effective heterojunction with the p‐type γ‐copper iodide (γ‐CuI) and n‐type gallium nitride (GaN) with excellent photodiode characteristics is demonstrated. The γ‐CuI/GaN heterojunction shows good rectification characteristics up to applied bias voltage of ±20 V with low saturation current, thus confirming the suitability of the γ‐CuI film. The heterojunction diode and ultraviolet (UV) photoresponsive characteristics of the device are elucidated with temperature‐dependent transport behavior analysis. With an increase in temperature, reverse saturation current is enhanced, whereas the diode ideality factor is reduced. The heterojunction device shows UV photoresponsive photovoltaic action with a prominent photovoltage of 0.93 V. The temperature‐dependent photovoltaic action is also investigated in the temperature range of 298–373 K, where the open circuit voltage (Voc) decreases with increase in temperature. The photovoltaic action is obtained at a temperature as high as 373 K, indicating that the γ‐CuI/GaN photoresponsive device is quite stable with excellent photovoltage. This study reveals that the effectiveness of γ‐CuI/GaN heterojunction and diode properties to fabricate a heterojunction photodiode with excellent photovoltage and photoresponsivity.