The Study Of Photodetectors With Graphene-based Composites

Graphene has attracted tremendous interests for optoelectronics and photodetection applications,because it can exhibit a fast response in a broad spectra due to its unique characteristics of zero bandgap and high carrier mobility at room temperature since its discovery in 2004.However,the responsivity of graphene-based photodetectors was limit to ¹0-2 A/W because of the weak light absorption.Quantum dots exhibit superior light absorption and tunable bandgap characteristics,thus higher responsivity and faster light response photodetectors are expected by combining the advantages of graphene and quantum dots.In this thesis,the fabrication process of graphene filed-effect transistor was developed,and some key processs to obtain graphene photodetectors with good properties were improved.Then,photodetector devices composed of PbS quantum dots and graphene,which hold the advantages of high absorption and carrier mobility have been fabricated and optimized The main results are as following:?1?The transfer process of graphene was developed and good quality graphene was obtained.First,we used oxygen plasma to etch graphene grown on the back of copper foil;Then,etching solution?HCl:H₂O₂:H₂O = 2:1:40?was used to effectively remove copper foil substrate;Finally,ammonia solution was introduced to neutralize p-doping of graphene from residual acid etchant.?2?Optimizing the key process of graphene photodetector fabrication.Firstly,we explored the proper lithography parameters which are used to make photoresist with a high slope angle that can completely remove the metal electrodes during lift off process;Secondly,we introduced an interlayer?PMMA?between the photoresist and graphene,and efficiently eliminated the polymer residue after patterning the graphene.?3?The optoelectric properties of monolayer graphene photodetector devices were studied and optimized.The optoelectric properties of devices were tested and analyzed,which exhibited ohmic contact behavior and bipolar characteristic of graphene;We also adopted several kinds of methods?such as reducing the concentration of PMMA in the graphene transfer process?annealing?formamide and ammonia solution immersion etc.?to reduce the p-type doping of graphene which can obtain high carrier?electrons or holes?mobility.?4?Fabrication method andoptoelectric properties of PbS QDs/Graphene hybrid photodetector were studied.We spined PbS QDs made of successive ionic layer adsorption and reation?SILAR?method on the TiO2 films which were deposited by electron beam evaporation method;Then,PbS QDs/Graphene hybrid photodetectors not only possess a high performance but also have a stable performance,were tested and analyzed,and the high performance is due to the synergistic function of photogating effect.The hybrid photodetectors obtain a specific detectivity over 1012 Jones,a high responsivity of 9.06 x 107 V/W and a fast response speed of 78 ms at rise time and 35 ms at delay time.