Controllable Synthesis And Photodetection Properties’ Improvement Of CdS Based Hybrid Structures

As a direct band gap semiconductor material, cadmium sulfide（CdS） is widely used in the optoelectronic field because of its excellent physical and chemical stabilities. However, pure CdS nanostructures can only absorb illumination whose wavelength is shorter than 510 nm, which is limited by the band gap of CdS. The responsivity and EQE values need some enhancement, too. We tried two methods: ion exchange and alloying to build CdS/PbS heterostructure and CdS_1-xSe_x to improve the electrical properties of CdS.We synthesized pure CdS nanowires by vapor phase method, and then carried out the ion exchange process in liquid phase. After ion exchange process, we got a 1D nanostructure like a CdS trunk with many PbS nanodots attaching on it. After the construction of device based on single CdS or CdS/PbS nanowire, we tested the opto-electrical properties of the devices. The response spectra of ion exchanged CdS/PbS heterostructure（650 nm） was found to be wider than the pure one（510 nm）. It also had a relatively higher responsivity and shorter response-decay time. The study of electronic band structures evidenced the change of band structure was attributed to the strain induced by the embedding of Pb ion.The alloying process was conducted by vapor phase synthesis. CdS powder and Se powder were choosed to be the source. Compounds of CdS_1-xSe_x nanowires can be controlled by changing the weight of Se powder, and the x values were calculated to be 0, 0.14, 0.31, 0.49, 0.70, 0.84. The band edge absorption wavelengths of Uv-Vis spectroscopy and photoluminescence（PL） peaks red shifted with the increase of Se concentration, which were corresponding with the band gap of samples. After the fabrication of devices based on different compounds of nanowires, we found that the devices have relatively high and fast response to the correnponding wavelength of light relative to their band gaps.