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The feasibility of van der Waals (VdW) heteroepitaxy of molybdenum disulphide (MoS2) layers on gallium nitride (GaN) semiconductor has attracted significant interest in heterojunction optoelectronic device applications. Here, we report on the growth of uniform MoS2 layers on free-standing GaN semiconductor for vertical heterojunction device application. A uniform MoS2 layer was directly grown on the n-type GaN wafer by sulphurization process of molybdenum oxide thin layer. Raman and scanning electron microscopy (SEM) analyses showed homogenous growth of the few-layers MoS2 forming a continuous film, considering the suitability of GaN semiconductor substrate. The fabricated MoS2/GaN vertical heterojunction showed excellent rectifying diode characteristics with a photovoltaic photoresponsivity under monochromatic light illumination. The X-ray photoelectron spectroscopy (XPS) studies showed the conduction and valence band offset values are around 0.44 and 2.3 eV with type II band alignment in the fabricated heterojunction device. This will facilitate effective movement of photoexcited electrons across the MoS2–GaN junction, while a large valence band offset will prevent movement of holes towards the GaN, resulting in low recombination loss to obtain a photovoltage in the heterojunction device. Our study revealed the formation of large-area homogenous MoS2 layers on GaN wafer for vertical heterojunction device application. [ABSTRACT FROM AUTHOR]

Fabrication of a two- and three-dimensional (2D/3D) heterojunction device has attracted significant attention for developing high performance photodiodes, light emitting diodes, solar cells, and other electronic devices. Here, we reveal the effect of ultraviolet (UV) illumination on electrical hysteresis in a graphene/gallium nitride (GaN) vertical heterojunction Schottky device. A chemical vapor deposited graphene film was transferred onto a free-standing n-type GaN substrate for Schottky diode fabrication, where the interfacial states play a significant role in the occurrence of electrical hysteresis in diode characteristics. A fabricated graphene/GaN Schottky device free from electrical hysteresis under no illumination condition showed the appearance of hysteresis with the illumination of UV light. The residual impurities of graphene and the surface defects of the GaN act as trap sites for the photocarriers; as a result, interface dependent photoresponsivity was observed. Capacitance-voltage analysis also showed the effect of residual impurities on the space charge dependent capacitance and the occurrence of hysteresis due to interface traps of the graphene/GaN heterojunction. Our findings can be significant in understanding the highly sensitive graphene/GaN and other 2D/3D heterojunction interfaces by the UV illumination process for developing high performance devices. [ABSTRACT FROM AUTHOR]

The heterostructures fabricated with a combination of 2-D materials and conventional semiconductors are of great interest owing to their unique optoelectronic properties. Here, we demonstrate the fabrication of a germanium (Ge)/MoS2 heterostructure and observation of a photovoltaic action with broadband photoresponsivity. A thin interface was formed in-between the thermally evaporated Ge and chemical vapor deposited MoS2 layers, considering the atomically smooth surface of MoS2. The current density-voltage (${J}$ – ${V}$) measurement showed a diode like characteristic and photoresponsivity under light illumination. The Ge/MoS2 heterojunction showed an open circuit voltage (${V}_{\text {oc}}$) of 0.185 V and short circuit current density (${J}_{\text {sc}}$) of 0.028 mA/cm2 under illumination of light (wavelength 350–1100 nm). The transient photoresponse characteristics of the Ge-MoS2 heterojunction device showed significant photoresponsivity for ultraviolet, visible, and near-infrared light at different bias voltages. The interfacial charge transfer at the Ge-MoS2 heterojunction is the critical aspect to create an effective build in field for the broadband photoresponsive device. The demonstrated ultrathin heterojunction of Ge and MoS2 layers can be significant for developing self-powered broadband photodetectors. [ABSTRACT FROM AUTHOR]

We demonstrate the fabrication of a monolayer graphene/β‐Ga2O3 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/Ga2O3 interface without any contribution from the trapped carriers. The fabricated device also shows an excellent photoresponsivity of 6.1 A W−1 with a slower response time at a low reverse bias voltage (−1.5 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‐Ga2O3 heterostructure can be significant for self‐powered/low power consuming DUV detector applications. [ABSTRACT FROM AUTHOR]

We demonstrate the fabrication of a solid state heterojunction photovoltaic device with solution-processed graphene oxide (GO) and n-Si. Partially reduced GO with a high optical gap (2.8 eV) was spin-coated on the n-Si substrate and a heterojunction device was fabricated with the structure of Au/pr-GO/n-Si. In the fabricated device, incident light was transmitted through the thin GO film to reach the junction interface, generating photoexciton, and thereby a photovoltaic action was observed. By means of a built-in electric potential at the GO/n-Si junction, photoexcited electrons and holes can be separated, transported and collected at the electrodes. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Demonstrated the formation of a heterojunction device with γ-phase copper iodide and beta-gallium oxide obtaining excellent photovoltage and photocurrent for solar-blind ultraviolet light irradiation. • Demonstrated the formation of a heterojunction device with γ-phase copper iodide and beta-gallium oxide. • Ultraviolet radiation-induced photovoltaic action is obtained with excellent photovoltage and photocurrent. • The heterojunction device showed a photovoltaic action under solar-blind radiation (254 nm) with photocurrent of 2.49 mA/W. • The obtained device properties of γ-CuI/β‐Ga 2 O 3 can be significant for self-powered UV photodetector applications. We report on the fabrication of γ-phase copper iodide (γ-CuI) and beta-gallium oxide (β-Ga 2 O 3) heterostructure device and obtaining the ultraviolet (UV) radiation responsive photovoltaic action. The crystalline γ-CuI with predominant (1 1 1) plane orientation was deposited on the β-Ga 2 O 3 by thermal evaporation process under vacuum condition. The electrical analysis revealed that the γ-CuI/β‐Ga 2 O 3 heterojunction possess an excellent rectifying diode characteristic with high rectification ratio and turn-on voltage. The fabricated heterojunction device showed a photovoltaic action under solar-blind UV irradiation (254 nm) with outstanding photovoltage of 0.706 V and photocurrent of 2.49 mA/W. The device also showed a photovoltaic action under illumination of 365 nm and 300–400 nm wavelength of UV light, corresponding to absorption due to the γ-CuI layer. The UV irradiation-induced photovoltaic action in the γ-CuI/β‐Ga 2 O 3 with outstanding photovoltage and excellent diode characteristics can be significant for self-powered UV photodetector applications. [ABSTRACT FROM AUTHOR]