Fabrication And Properties Of Photodetectors Based On Graphene And PbSe Quantum Dots

Graphene is a new type of zero-band gap semi-metallic two-dimensional material with excellent properties such as wide spectral absorption range,high carrier mobility and fast response.It has important application prospects in electronic information,materials,micro-nano processing,energy,biomedicine and other fields,and is considered as a revolutionary material in the future.However,due to the zero band gap structure of graphene,its light absorption capacity is relatively weak（the absorption rate is only 2.3%in a wide wavelength range）,and there are some shortcomings such as small gain mechanism and fast recombination rate of carriers,which limit the application of pure graphene in photodetectors.Semiconductor quantum dot materials have attracted much attention in recent years because of their unique physical and chemical properties,such as wide absorption spectrum,narrow emission spectrum and tunability.Therefore,the composite heterojunction photodetector based on graphene-based semiconductor quantum dots has become a research hotspot in this field.In this paper,graphene-quantum dot composite heterojunction photodetectors are fabricated based on graphene and quantum dots,which can combine the high carrier mobility of graphene with the excellent optoelectronic properties of quantum dot materials,prolong the carrier lifetime and improve the gain of the device.it provides a research idea for the preparation of photodetectors with wide spectral response,high responsiveness and high sensitivity.In this paper,large area graphene thin films were directly grown on Si O2/Si insulating substrate by plasma enhanced chemical vapor deposition（PECVD）.The defects,surface morphology and transmittance of graphene were tested and characterized by Raman spectrum analyzer,scanning electron microscope（SEM）,atomic force microscope（AFM）and ultraviolet-visible photometer（UV-Visspectrophotometer）.The preparation conditions were optimized and a few layers of graphene with large area,high transmittance and high mobility were obtained.Furthermore,based on the structure of the field effect transistor,the source and drain electrodes were prepared on the graphene thin film by magnetron sputtering mask method,and the graphene-based photodetector with channel length of 30μm was obtained.Then,the photoelectric performance of graphene-based photodetector was tested by Keithley4200A parameter analyzer.The test results show that good ohmic contact is formed between graphene and electrode,graphene has bipolar characteristics.Under the irradiation of 405nm,515 nm and 650 nm light,the device has obvious light response,and its light responsivity is283.3 A·W^-1,58.4 A·W^-1 and 41.7 A·W^-1 respectively,which indicates that the pure graphene photodetector can effectively detect the light in the visible light band.Finally,PbSe QDs were prepared and characterized.The test results show that the quantum dots have good dispersion,and the particle size is 6.3 nm.Graphene/PbSe QDs composite heterojunction photodetector was prepared by compounding PbSe QDs with graphene.The test results show that the composite heterojunction device responds to the light of 280 nm,405 nm,515nm and 650 nm,indicating that the heterojunction device can detect the light in the range of ultraviolet to near-infrared band,and the maximum response is 700.8 A·W^-1 and the detection rate is 2.78×10¹¹Jones under the irradiation of 405 nm light.Composite heterojunction devices have the advantages of wide spectrum detection range and small dark current.