Search

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.

We report on the fabrication of γ-phase copper iodide (γ-CuI) and beta-gallium oxide (β-Ga2O3) 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-Ga2O3 by thermal evaporation process under vacuum condition. The electrical analysis revealed that the γ-CuI/β‐Ga2O3 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‐Ga2O3 with outstanding photovoltage and excellent diode characteristics can be significant for self-powered UV photodetector applications.