Infrared Photodetector Based On PbS_xSe_1-x Colloidal Quantum Dots

As an important part of nanostructured optoelectronic devices, the nanocomposite film photodetector combines the quantum effect and size effect of nanomaterials with the photoconductive effect of semiconductors effectively, and it has received much concern due to its excellent properties and wide application prospects. The nanocomposite film photodetector with field-effect transistor(FET) configuration can overcome the shortcomings of quick exciton quenching and low optical gain for conventional photodetectors, in this way, it can not only possess the excellent response properties but the function of signal amplification and easiness to be integrated. By introducing organic conjugated molecules with planar quantum dots properties into the nanocomposite film photodetector with FET configuration, it can not only achieve high carrier transport and enhance the detecting performance, but also can simplify the fabrication processes. Colloidal quantum dots(CQDs) attract wide attention for its properties such as quantum size effect, multiple exciton effect, and so on. Most of all, IV-VI quantum dots(QDs), such as Pb S and Pb Se QDs, have been widely used in the field of infrared optoelectronic devices. Ternary Pb SxSe1-x quantum dots are alloyed nanocrystals(NCs) consisting of Pb S NCs and Pb Se NCs which its absorption spectrum can be controlled by adjusting the ratio of S and Se. Also, Pb SxSe1-x CQDs can yield more efficient photovoltaic cells with higher JSC and VOC which is unavailable for either pure Pb S or pure Pb Se. Therefore, conjugate molecules and semiconductor quantum dots are tentatively used to fabricate novel photodetectors in this work, and we hope it can provide some useful data for the applications of infrared photodetectors in the future. The main results can be summarized as following:(1) By using the hot-injection method, we used Pb O to act as the source of lead and Se powder as the source of Se, TMS2 S as the source of S, Pb SxSe1-x quantum dots with particle sizes about 4nm have been successfully synthesized. The absorption peak can be adjusted from 1100 nm to 1500 nm as varying the relative weight ratio of S and Se in the precursor. Our experimental data confirmed that the quantum dot size and its absorption peak can be changed by controlling the reaction condition.(2)We blended poly(3-hexylthiophene)(P3HT) and Pb S0.4Se0.6 quantum dots together and used the blended Pb S0.4Se0.6:P3HT nanocomposites as the active layer, organic polymer PMMA as the dielectric layer, we fabricated FET-based infrared photodetector Au/Pb S0.4Se0.6:P3HT/PMMA/Al. Our experimental data showed that the photodetector had shown good detecting performance and the maximum specific detectivity can reach 1.02′1010 Jones.(3) We fabricated FET-based solution-processed colloidal quantum dot photodetector Au/Pb S0.4Se0.6:P3HT/PMMA/Al and further explored the influence of the weight ratio of P3 HT to Pb S0.4Se0.6 in the active layer. The electrical characteristics and the detecting parameters of the four devices in different weight ratio(K=MP3HT:MCQDs, K =2:1, 1:1, 1:2, 1:3) were compared with each other in dark and under 980 nm illumination with different incident intensities. A maximum responsivity and specific detectivity of 55.98 m A/W and 1.02′1010 Jones at low source-drain voltage(VDS) of-10 V and gate voltage(VG) of 3 V were obtained for K=1:2 under the 980 nm laser with an illumination intensity of 0.1 m W/cm2.