Experimental Study On Mixed-dimensional Heterostructure Based On Graphene For Optoelectronic Devices

Various researches based on graphene have attracted scholars' and engineers'attention worldwide since the discovery of graphene.Graphene,with several unique characteristics including visible transparence,extraordinarily high carrier mobility,broadband spectrum absorption,has become raw materials of solar cell,photodetector,light-emitting diode and other devices.Graphene has zero bandgap because its'valence and conduction band intersect at a point called Dirac point where Fermi level of pure graphene locates.The density of states near the Dirac point is ultralow,thereby the Fermi level of graphene can be tunable easily by injecting carrier.In this paper,combining with unique characteristics of graphene,the viable way of multi-type quantum dots photo-induced doping has been demonstrated to enhance the power conversion efficiency of graphene/GaAs heterostructure solar cell.We found that trilayer graphene/GaAs heterostructure could detect the incident light at wavelength of 980 nm,then the anti-stokes properties of rare earth ions have been used to improve the performance of this photodetector.We designed the completely new device coupling with both photo-induced doping by Si quantum dots and surface plasmon resonance of Au nanoparticles.The major contributions of this thesis include:(1)Graphene/GaAs heterostructure solar cell has been designed.The maximal power conversion efficiency of this device was 8.57%and short-circuit current density,open-circuit voltage and fill factor were 17.80 mA/cm2?0.67V?71.80%,respectively.This performance could be ascribed to the good technologies of fabrication besides Ohmic Contact of low contact resistance and good surface passivation.ZnO,InP quantum dots have been coated onto the front surface of graphene/GaAs heterostructure solar cell,leading to improving by 34.19%,from 8.57%to 11.57%.The reason of this improvement could be attributed to injecting electrons from quantum dots to graphene,which was be demonstrated by fluorescence quenching of quantum dots.In this situation,the location of Fenni level could be changed,leading to the enhancement of the height of barrier and the width of depletion layer.(2)Trilayer graphene/GaAs heterostructure photodetector which could detect the incident light at wavelength of 980 nm has been designed.The energy of photon(1.26 eV)at wavelength of 980 nm is less than the energy of band gap of GaAs(1.42 eV).The responsivity and detectivity were 2.31 mA/W,3.40×1010 cm Hz0 5/W,respectively.The performance of this photodetector could be improved by upconversion nanoparticles because of radiative energy transfer,non-radiative energy transfer and antireflection.After the introduction of upconversion nanoparticles,the responsivity and detectivity increased from 2.31 mA/W to 5.97 mA/W,and 3.40×1010 cm Hz0.5/W to 1.10×1011 cm Hz0.5/W,respectively.(3)Completely new devices coupling with both photo-induced doping by Si quantum dots and surface plasmon resonance of Au nanoparticles has been designed and finished.After coating the nanoparticle and quantum dots,the photocurrent of this new device increased from 1.73 uA to 2.60 uA under the illumination at the wavelength of 532 nm with of power of 5.5 uW.The responsivity and detectivity were 470 mA/W(1.81×105 V/W),2.0×1012 cm Hz0.5/W,respectively.(4)The stability of these devices in the air has been demonstrated.The power conversion efficiency reduced by 0.61%after ten days,and the power conversion efficiency of another device decreased from 8.35%to 7.35%after two years,indicating the stability of these devices.