The Preparation Of Quantum Dot Device And The Study Of Electron Transport

Quantum dots as a key part of the quantum computing devices,are attracting more and more attention due to their good scalability.Through the control of the spin state,the semiconductor quantum dots can be integrated into the semiconductor chip for quantum computation.In this thesis,graphene quantum dot based devices were fabricated.The basic transport properties of graphene quantum dots were studied.We prepared quantum dots on graphene that was produced by chemical vapor deposition and mechanical exfoliation,respectively.We optimized the preparation techniques made tests on graphene quantum dots.Our main research is as follows:1.The time evolution of the electrical properties in different environments is analyzed by Raman spectroscopy.It is found that the graphene monolayer is susceptible to electron irradiation.The presence of D peaks in graphene Raman spectroscopy indicates that electron beam irradiation introduces defects in graphene lattice.The carrier type and electrical resistivity of graphene can be varied over a wide range by electron beam irradiation.This shows that electron beam irradiation can be used as a new defect engineering method to change the properties of graphene.The results are very important for the preparation and measurement of graphene nano-devices involving electron beam irradiation(such as scanning electron microscopy and electron beam exposure),and pave the way for optimizing the processes and techniques for preparation of quantum dots.2.Through a large number of experiments,we opimized the processing parameters for preparing quantum dots by electron beam exposure,which include beam current,writing field,focusing,dosage,proximity effect compensation.The exposure accuracy and the aspect ratio we achieved are up to <20 nm and 4:1,respectively,which has set a good basis for precise and controllable preparation of quantum dots.3.Using UV lithography and electron beam lithography,graphene quantum dot devices were prepared on CVD graphene.The preparation of the device was carried out by photo lithography,electron beam evaporation,oxygen plasma etching,electron beam exposure,reactive ion etching and bonding.The key parameters of quantum dots were obtained,such as UV exposure time,Alignment accuracy and development time,electron beam deposition rate,oxygen plasma etching power,etch time,reactive ion etching time,gas selection ratio,power,and electron beam lithography parameters.The controllable preparation of graphene quantum dots is realized and the mass production of graphene quantum dot devices is preliminarily attempted.4.The graphene quantum dot devices were fabricated from the mechanical exfoliation by electron beam lithography.The quantum dot devices with potential barrier resistance in the range of 25.8 to 1000 k? were picked out and tested at low temperatures.Based on the measured Coulomb blockade effect and the Coulomb diamond,the desired graphene quantum dot devices were sifted out.