Lead sulfide (PbS) quantum dots (QDs) have attracted a great deal of attention in recent decades, due to their value for applications in optoelectronic devices. However, optimizing the performance of optoelectronic devices through ligand engineering has become a major challenge, as the surfactants that surround quantum dots impede the transport of electrons. In this paper, we prepared PbS QD films and photoconductive devices with four different ligands: 1,2-ethylenedithiol (EDT), tetrabutylammonium iodide (TBAI), hexadecyl trimethyl ammonium bromide (CTAB), and sodium sulfide (Na2S). A series of characterization studies confirmed that using the appropriate ligands in the solid-state ligand exchange step for thin film fabrication can significantly improve the responsivity. The devices treated with sodium sulfide showed the best sensitivity and a wider detection from 400 nm to 2300 nm, compared to the other ligand-treated devices. The responsivity of the champion device reached 95.6 mA/W under laser illumination at 980 nm, with an intensity of 50 mW/cm2.

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Light loss is one of the main factors affecting the quantum efficiency of photodetectors. Many researchers have attempted to use various methods to improve the quantum efficiency of silicon-based photodetectors. Herein, we designed highly anti-reflective silicon nanometer truncated cone arrays (Si NTCAs) as a light-trapping layer in combination with graphene to construct a high-performance graphene/Si NTCAs photodetector. This heterojunction structure overcomes the weak light absorption and severe surface recombination in traditional silicon-based photodetectors. At the same time, graphene can be used both as a broad-spectrum absorption layer and as a transparent electrode to improve the response speed of heterojunction devices. Due to these two mechanisms, this photodetector had a high quantum efficiency of 97% at a wavelength of 780 nm and a short rise/fall time of 60/105µs. This device design promotes the development of silicon-based photodetectors and provides new possibilities for integrated photoelectric systems.

The carrier gas flow field plays a vital role in the chemical vapor deposition (CVD) process of two dimensional (2D) MoS2 crystal, which was studied by simulations and experiments. Different carrier gas flow fields were studied by utilizing three types of precursor carrier which affected the local gas flow field significantly. The experiment results showed that the appropriate precursor vapor concentration could be achieved by local carrier gas flow field conditioning, resulting in single 2D MoS2 crystals of a large size and a high coating rate of 2D MoS2 crystal on the target substrate surface. The carrier gas flow also contributed to the growth of the 2D MoS2 crystal when it flew towards the target surface. The size of deposited single 2D MoS2 crystal reached tens of micrometers and a few layers of 2D MoS2 crystal were characterized and confirmed.

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