Fig. 1. (a) Illustration of the SL MoS2-on-GaN structure. (b) Due to the electron-phonon coupling between MoS2 and GaN, the calculated absorption coefficient of the SL MoS2 layer is increased significantly in the visible region.

Fig. 2. (a) Illustration of SL MoS2 growth process by CVD under Ar atmosphere. The FS-GaN substrate was placed upside down on the center of the crucible, and the SL-MoS2 was grown on the Ga-face. The growth condition was 750°C lasting for 10 min. (b) Raman spectrum of SL-MoS2 on FS-GaN. (c) Cross-sectional transmission electron microscopy (TEM) image of the MoS2 grown on the GaN substrate. The measured MoS2 film thickness is ∼0.7  nm, indicating a single layer of MoS2. (d) Absorbance of SL MoS2 on the FS-GaN substrate as a function of incident wavelength. The strongest absorption is at around 430 nm.

Fig. 3. (a) Schematic diagram of the preparation steps of monolithic integration of GaN-based UV detectors and MoS2-based visible detectors. Photoresist was used for mask, and part of the SL MoS2 was etched by Ar plasma. Standard photolithography was applied, and a 50 nm Au electrode was fabricated by electron beam evaporation for the whole wafer. (b) Optical microscope image of monolithic integration of GaN-based and MoS₂-based detectors. The reference scale in the image is 100 μm. (c) 3D schematic view of the MoS2/GaN monolithic integration device. Top view photo image of 1  cm×1  cm size sample fabricated is shown in the inset.

Fig. 4. (a) Dark current and light current for 280 nm incident light under different powers of the GaN PD. (b) Dark current and light current for a 405 nm laser under different incident powers of the MoS2 PD.

Fig. 5. (a) Responsivity R (A/W) and photocurrent (μA), (b) photoconductive gain G and external quantum efficiency (EQE), and (c) noise equivalent power (NEP) and normalized detectivity D* of the GaN PD as functions of incident power under a fixed voltage of 20 V. (d) Responsivity R (A/W) and photocurrent (mA), (e) photoconductive gain G and external quantum efficiency (EQE), and (f) noise equivalent power (NEP) and normalized detectivity D* of the MoS2 PD as functions of incident power under a fixed voltage of 3 V.

Fig. 6. Photocurrent as a function of time under alternative dark and illumination. (a) Photocurrent-time curve of GaN illuminated by a 280 nm light source with the incident power of 15.01 nW at 20 V. (b) The rise time (from 10% to 90% of maximum photocurrent) and the fall time (from 90% to 10% of maximum photocurrent) of the GaN PD. (c) Photocurrent-time curve of MoS2/GaN illuminated by a 405 nm laser with the incident power of 10 mW at 3 V. (d) The rise and fall time of the MoS2/GaN PD.