| IV-VI colloidal quantum dots are a kind of direct bandgap semiconductor materials, which have obvious advantages, such as quantum size effect, surface effect and multiple exciton generation(MEG), therefore they can be widely used in the fields of infrared photodetector, biological tracer, solar cell, optical fiber communication and so on. In recent years, the synthesis of near infrared semiconductor quantum dots such as HgTe, InP, PbS, PbSe, In As and PbTe, have developed rapidly, especially the lead chalcogenide quantum dots(such as PbSe and PbS) have unique advantages over other materials. Recently, interests in lead selenide(PbSe) colloidal quantum dots(CQDs) are particularly intense due to its properties of narrow bandgap of bulk(0.28 eV), large exciton Bohr radius(46 nm), high dielectric constant(εm= 23) and its absorption spectrum can be adjusted to a great extent with a great blue-shift relative to that of the bulk material, making PbSe CQDs ideal material for various IR optoelectronic devices. However, PbSe quantum dots are sensitive to Oxygen and water in air, so it is urgent for us to optimize the chemical properties of PbSe semiconductor quantum dots with a high stability and particle size-controllability.In order to obtain stable PbSe QDs, therefore in our experiment, PbSe QDs were synthesized following the method reported by Yu et al with some modification. By using hot injection method, we synthesized PbSe CQDs with lead oxide(PbO) acting as the source of lead and selenium powder as selenium source. The particle sizes of PbSe QDs vary from 3 nm to 5 nm and its absorption peak can be adjusted from 700 m to 2000 nm. Our experimental data confirmed that the particle size of the quantum dot can be controlled by controlling the reaction time. After the reaction being terminated, the temperature of solution was droped to 60 °C by transferring the flask into an ethyl alcohol bath. Then we used a post-synthetic halide salt(i.e. NH4Cl) to treat the PbSe CQDs, in other words, NH4 Cl was added into the reaction solution after the CQDs growth was halted. The mixture was then incubated for 10 min at 60°C. Then we get stable PbSe powders and it can be kept as long as 41 days in air. The preparation method is simple, and the requirements for the processing environment are not high, furthermore, the PbSe QDs-based devices do not need to be matched with the substrate, therefore the PbSe QDs-based devices can be prepared by the solution process with the low cost and large size. In our experiments, we have fabricated high performance infrared photodetector, in which Pb Se acts as the active layer. After a series of experiments, we have reached the following main conclusions:(1) By using hot injection synthesis method, in which lead oxide(PbO) acts as the source of lead, selenium powders as selenium source, we get nanoparticle sizes of PbSe quantum dots from 3 nm to 5 nm, their absorption peaks can be adjusted between 700 nm and 2000 nm. Our experimental results show that the particle size of the quantum dot can be controlled by controlling the reaction time.(2) As compared with other literatures, some changes have been made for the synthesis of PbSe, in which Pb2+ was coated with Cl- on the surface during the process of synthesis, thus avoids the contact between Pb2+ and air, in this way, we obtained stable PbSe quantum dot powder.(3) We have fabricated solution-processed high-performance infrared photodetector with a field-effect transistor(FET) configuration by reversely fabricating the PbSe active layer and polymethylmethacrylate(PMMA) dielectric layer. The responsivity and the specific detectivity of the FET-based photodetector Au(Source, Drain)/PbSe(52nm)/PMMA(930nm)/Au(Gate) reached 64.17 mA/W and 5.08×1010 Jones, respectively, under 980 nm laser illumination with an intensity of 0.1 mW/cm2. Therefore, it provides a promising way to make high-sensitivity near-IR/mid-IR photodetector. |
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