Study On The Graphene/Silicon Hybrid High-Gain Photodetector

Photodetectors are important devices of converting optical signals into electric signals and have been widely used in the civil and military fields,such as the areas of medical,security,sensor detection,night vision imaging,etc.With many years'development,the traditional photodetectors based on semiconductor materials such as silicon and germanium have been encountering bottleneck in terms of gain,which becomes more and more obvious.As a result,it is urgent to find new materials for the fabrication of high-gain photodetectors.Since reported in 2004 graphene has attracted tremendous attention from the researchers working in semiconductor and electronic device areas,due to its ultra-high carrier mobility,ultra-wide absorption spectra,and stable physical structure and chemical properties.Recently,photodetectors fabricated from hybrid materials containing graphene have been developed,showing great potential in high-gain photoelectric conversion.However,the properties of this type of photodetectors are greatly influenced by the size of carrier channels,making it difficult to compare the photoelectric characteristics of the same type of devices.Therefore,in this project we have studied the dependence of the photoelectric properties on the carrier channel size,and the relationship between the carrier channel size and theoretical calculated noise.The work in this project mainly includes three parts:(1)first,high-quality graphene films were obtained by chemical vapor growth,wet transfer,photolithography,vapor deposition etching,etc.By combining the film with intrinsic silicon and metal electrodes specific-patterned photodetectors were fabricated.(2)second,the properties such as optical structure,light/dark current,responsivity and detectivity of graphene/intrinsic silicon hybrid photodetectors with different sizes were characterized and analyzed using optical and electrical instruments.The effects of carrier channel size on the gain of photodetectors have been revealed.The net photocurrent and the specific detectivity increasing with the increase of the carrier channel size were disclosed.(3)finally,low frequency noise of the photodetector was measured,and it was found that both the voltage and current of the noise decrease with the increase of the carrier channel length.The measured noise current was also compared with the noise current calculated from the theoretical shot noise model.Through systematic study carried out in this project,it can be concluded that the photoelectric properties of graphene/silicon hybrid photodetector is related to the carrier channel size and that the shot noise model is not suitable for the evaluation of the low frequency noise current.The results obtained from this work are helpful and instructive for the design and assessment of graphene-based hybrid high-gain photodetectors,which can promote the practical application of this type of photodetectors.