Research On Photoelectric Detection Performance Based On Hybrid Quantum Dots

Semiconductors composed of?-?compounds are a material with narrow band gap width,which has been concerned and researched by researchers since the 1930s,such as Pb S,Pb Se,Pb Te and so on.Low-dimensional materials,a kind of new materials,was discovered in the 1980s and they have attracted much attention and been widely studied because of their unique quantum effect.As a kind of zero-dimensional materials,quantum dots(QDs)own more significant quantum effects,so they are widely used in the fields of photodetectors,biomarkers,solar cells and light-emitting diodes.Moreover,with the research on the synthesis method of quantum dots,it is found that the thermal-injection method is an excellent method to synthesis colloidal quantum dots with low cost,simple process,stable performance and good uniformity,which is helpful to prepare low-cost quantum dot photodetectors and study their optoelectronic properties.Bulk materials of Pb S and Pb Se have very narrow band gap widths of 0.41ev and 0.26ev,and have large Bohr radius and the quantum dots of Pb S and Pb Se can be synthesized simply and stably by thermal-injection method.Based on those,a near-infrared photodetector of photovoltaic field-effect transistor structure based on quantum dot is prepared in this dissertation.Firstly,based on the growth mechanism of colloidal particles,Pb Se colloidal quantum dots(Pb Se-CQDs)with different sizes were synthesized by thermal-injection method.At the same time,Pb Se quantum dots with average particle sizes of 4.98nm,5.22nm,5.82nm,6.75nm,7.45nm and 8.11nm were prepared by controlling the synthesis time in 1-5min.The analysis shows that with the increase of the size of colloidal quantum dots,the absorption peak of its spectrum is also gradually shifted to the long wave direction.In order to enhance the stability of the quantum dots,in-situ synthesis post-halide salt treatment was used to passivate the quantum dots.NH₄Cl was added to the solution to coat the surface of the quantum dots with a layer of Cl^-,which can enhance the stability of quantum dots.Then the structure and principle of photovoltaic field effect phototransistor based on quantum dot are analyzed.The incident light irradiates the surface of quantum dot to produce photovoltaic voltage,which can adjust the width of the channel and enhance its conductivity.Then,the substrate of photovoltaic field effect phototransistor is prepared by these processes of lithography,magnetron sputtering and etching,and then the photovoltaic field effect phototransistor based on quantum dot are prepared by spinning quantum dots on the substrate.The photoelectric properties of quantum dots with different thickness are tested,analyzed and compared.Among them,the structure of the 8-layer quantum dot layer has better performance,with the responsivity of 113.3A/W,the detectivity of 6.59*10~9Jones(@450nm,30?W/cm~2)and the responsivity of 46.7A/W,the detectivity of 2.71*10~9Jones(@1310nm,60?W/cm~2).At the same time,it owns a fast response time,the rise time of 20.6?s,and the fall time of 68.5?s.Subsequently,a mixed structure of quantum dots with different absorption peaks was prepared to improve its response at the bottom before the absorption peak.The mixed structure formed by quantum dots of Pb Se-1580nm and Pb S-1290nm,Pb Se-1580nm and Pb Se-1672nm is tested its improvement at the bottom of the spectrum.Compared with the response at1310nm and 1550nm,they increased by about 25.4%and 20.9%respectively at 1310nm near the bottom of pbse-1580nm spectrum.