Salt‐Assisted Growth of P‐type Cu₉S₅ Nanoflakes for P‐N Heterojunction Photodetectors with High Responsivity

Abstract

P‐n junctions based on two dimensional (2D) van der Waals (vdW) heterostructure are one of the most promising alternatives in next‐generation electronics and optoelectronics. By choosing different 2D transition metal dichalcogenides (TMDCs), the p‐n junctions have tailored energy band alignments and exhibit superior performance as photodetectors. The p‐n diodes working at reverse bias commonly have high detectivity due to suppressed dark current but suffer from low responsivity resulting from small quantum efficiency. Greater build‐in electric field in the depletion layer can improve the quantum efficiency by reducing recombination of charge carriers. Herein, Cu9S5, a novel p‐type semiconductor with direct bandgap and high optical absorption coefficient, is synthesized by salt‐assisted chemical vapor deposition (CVD) method. The high density of holes in Cu9S5 endows the constructed p‐n junction, Cu9S5/MoS2, with strong build‐in electric field according to Anderson heterojunction model. Consequently, the Cu9S5/MoS2 p‐n heterojunction has low dark current at reverse bias and high photoresponse under illumination due to the efficient charge separation. The Cu9S5/MoS2 photodetector exhibits good photodetectivity of 1.6 × 1012 Jones and photoresponsivity of 76 A W−1 under illumination. This study demonstrates Cu9S5 as a promising p‐type semiconductor for high‐performance p‐n heterojunction diodes.

Self‐Driven WSe2/Bi2O2Se Van der Waals Heterostructure Photodetectors with High Light On/Off Ratio and Fast Response

“…[ 41 ] Apparent reduction of Raman intensity called “Raman quench” indicated a strong interfacial coupling between the two flakes. [ 40,42,43 ] The Raman mapping of Bi 2 O 2 Se (159 cm −1 ) and WSe 2 (256 cm −1 ) (Figure 1f,g) further confirms the high‐quality of the heterostructure, exhibiting a great homogeneity of each component. We also collected the PL spectra from different areas (Figure 1e) and found no obvious PL signal was observed for bare Bi 2 O 2 Se due to the intrinsic indirect optical bandgap, [ 18,20 ] but strong excitonic emission around 775 nm of bare WSe 2 .…”

“…[ 37 ] On the contrary, when WSe 2 /Bi 2 O 2 Se heterostructure device operated under −5 V as shown in Figure 4c, the light on/off ratio enhanced to 618 (532 nm @ 52.37 mW cm −2 ) and a decent photoresponsivity of 638 mA W −1 (1.12 mW cm −2 ) in the WSe 2 /Bi 2 O 2 Se photodiode is also comparable to those of reported literature. [ 41,43,47,52,57 ] By fitting the light intensity ( P ) dependent I ph through the equation of I ph ∝ P α (Figure 4d), it was found that I ph at V ds = +5 V was relatively larger than 10 −6 A level with the α = 0.38, which indicated the existence of photogating effect and high photogain. [ 34 ] Therefore, the WSe 2 /Bi 2 O 2 Se heterostructure could operate as photodiode with high photoresponse and high sensitivity as the photoswitching characterization in Figure S6a,b, Supporting Information.…”

A review of molybdenum disulfide (MoS2) based photodetectors: from ultra-broadband, self-powered to flexible devices

“…The performance of self-powered MoS 2 photodetectors can be enhanced due to the piezoelectric effect. 221,258,272 MoS 2 based self-powered broadband photodetectors have been reported for n-MoS 2 /n-GaAs, 438 MoS 2 /b-Ga 2 O 3 , 439 Pd-MoS 2 /Si, 440 Pd/Al 2 O 3 /MoS 2 , 441 Pd/HfO 2 /MoS 2 , 441 graphene/InSe/MoS 2 , 442 p-Cu 9 S 5 /n-MoS 2 , 443 and MoS 2(1Àx) -Se 2x . 385,386,435 MoS 2 based self-powered photodetectors exhibit photoresponsivity from mA W À1 to A W À1 , detectivity from 10 9 to 10 15 Jones and response time from microseconds (ms) to seconds (s), depending on the measurement wavelengths and incident power densities which could be used for healthcare applications.…”

Dual‐Mode Wearable Strain Sensor Based on Graphene/Colloidal Crystal Films for Simultaneously Detection of Subtle and Large Human Motions

“…The excellent recoverability of the CCF sensor make it suitable for attaching into the skin for continuous and long-term detection of an individual's motion. Furthermore, the elastic non-close-packed CCFs have a broad sensing range up to 68% strain, that is clearly higher than that of the recently reported elastic close-packed CCFs, [32] inverse opals film and organic CC gel, [33,34] and can satisfy the detection of large human motion, such as joint bending movements up to ≈55% strain. However, the CCF sensors exhibits no obvious, naked-eye visualized color change when the stretching strain is <10% (Figure 3a) and cannot satisfy the detecting subtle human motion, such as respiratory and pulse movements.…”

“…Up to now, various flexible mechanochromic PCs including inverse opal colloidal crystal films (CCFs), colloidal particles embedded in elastomers have been developed for the visualized detection of strain. [32][33][34][35][36][37] However, for the practical application of PCs as mechanochromic sensors, these sensors are usually employed to detect large strain and cannot satisfy the detection of subtle strain because simple naked-eye detection of colorimetric changes require sufficiently large mechanochromic deformation of PCs that must be induced by the strain.…”