Fig. 1. Fabrication processes for integrating TiN NPs array and Al2O3 with WSe2 photodetector. (a) Cleaning the glass substrate. (b) Preparing PS nanospheres template on the glass substrate. (c) Etching the PS nanospheres template with O2. (d) Sputtering of TiN on the etched PS nanospheres template. (e) Removal of PS nanospheres template by acetone and obtaining an ordered TiN NPs array. (f) Deposition of Al2O3 on the surface of TiN NPs array. (g) Transfer of WSe2 onto the glass/TiN NPs/Al2O3 substrate. (h) Schematic diagram of the WSe2 photodetector after sputtering the TiN electrodes.

Fig. 2. AFM images of (a) the well-ordered and closely-packed monolayer PS nanosphere template and (b) the hexagonal arrangement TiN NPs after sputtering of TiN film and removal of the bottom PS nanosphere template by acetone. (c) Experimental absorption spectra of the single WSe2 and the heterostructure of TiN NPs/WSe2 with a 40 nm thick TiN NP layer. (d) Comparative electric field distributions of the single WSe2 and TiN NPs/WSe2 films at the wavelength of 850 nm.

Fig. 3. I–V curves of the WSe2, TiN-NPs/WSe2, and TiN-NPs/Al2O3/WSe2 devices (a) in the dark and (b) under 660 nm illumination with an intensity of 10.2  mW/cm2. (c), (d) Transient responses for TiN-NPs/Al2O3/WSe2 and single WSe2 PDs under different wavelengths, ranging from 375 nm to 1550 nm, under the bias of 2 V. The thickness of the Al2O3 layer is 1 nm.

Fig. 4. (a) EQE and R, and (b) EQE enhancement factor of the single WSe2 PD and the TiN-NPs/Al2O3/WSe2 PD with a 1 nm thick Al2O3 layer. LDR characteristics of the TiN-NPs/Al2O3/WSe2 PD at (c) 505 nm and (d) 850 nm.

Fig. 5. (a) Raman spectra measured for the WSe2, Al2O3/WSe2, and TiN NPs/Al2O3/WSe2 films. Working mechanism of the (b) single WSe2 and (c) TiN-NPs/Al2O3/WSe2 device in the UV and visible wavelength range. (d) Energy band diagram of the TiN-NPs/Al2O3/WSe2 interfaces illustrating hot electrons excitation and transfer in the NIR and telecommunication range. Working mechanism of (e) the single WSe2 device and (f) TiN-NPs/Al2O3/WSe2 device in the near infrared and telecommunication range.

Fig. 6. Absorption spectra of TiN NPs with different (a) deposition thicknesses and (b) incident angles.

Fig. 7. AFM image of oxygen etched PS nanospheres with the thickness of 40 nm.

Fig. 8. (a) Simulated absorption spectra and (b) absorption enhancement factor of single WSe2 film and TiN-NPs/Al2O3/WSe2 film.

Fig. 9. Electric field distributions of the TiN NPs/WSe2 films at the wavelength of (a) 385 nm, (b) 505 nm, (c) 660 nm, and (d) 850 nm.

Fig. 10. (a)–(e) The I–V curves of TiN-NPs/Al2O3/WSe2 PD with different thicknesses of Al2O3 layer in the dark and under illumination of 980 nm laser with the intensity of 10.2  mW/cm2. (f) The photocurrent to dark current ratio (IP/ID) for TiN-NPs/Al2O3/WSe2 PD with different thicknesses of Al2O3 layer in (a)–(e).

Fig. 11. The I–V curves of TiN-NPs/Al2O3/WSe2 and single WSe2 PDs in the dark and under different illuminations with the intensity of 10.2  mW/cm2: (a) 375 nm, (b) 505 nm, (c) 660 nm, (d) 850 nm, (e) 980 nm, (f) 1120 nm, (g) 1208 nm, (h) 1310 nm, and (i) 1550 nm.

Fig. 12. The response time of (a), (b) TiN-NPs/Al2O3/WSe2 device and (c), (d) WSe2 device in the visible and near infrared wavelength ranges.

Fig. 13. The log I versus log V plot in the dark of WSe2, TiN-NPs/WSe2, and TiN-NPs/Al2O3/WSe2 devices.

Fig. 14. Surface potentials and work functions measured for (a) TiN-NPs and (b) WSe2.