Growth Of Graphene On Germanium And Photoelectric Properties Of Graphene/Germanium

Photodetector,as a kind of photoelectric device that can convert optical signal into electrical signal,it has a wide application prospect in military monitoring,weather prediction,biological/chemical sensing and other fields.In recent years,more and more researchers try to use two-dimensional materials to build photodetectors in order to solve the shortcomings of traditional photodetectors,such as large size,high energy consumption and low performance.Two dimensional materials are expected to be indispensable building materials in the next generation of optoelectronic devices due to their excellent electronic transport properties and tunable band gap.Among them,single-layer and few layer graphene have been widely used in photodetectors due to their high carrier mobility,unique optical properties and superior mechanical flexibility,showing very fast light response speed and high light response rate.At present,the growth of graphene on metal substrate by chemical vapor deposition（CVD）requires a complicated wet transfer process to transfer it to the target substrate,so as to realize the application of graphene.However,this process usually damages the structure of graphene and leaves unnecessary surface pollution.Based on the above analysis,this paper studies the synthesis of graphene by chemical vapor deposition on non-metallic germanium substrate and the dry transfer of graphene,and further studies the photoelectric performance of graphene/germanium photodetector under visible light and near-infrared light.In this paper,low pressure chemical vapor deposition（LPCVD）was used to grow graphene on germanium substrate.The effects of temperature（900℃,910℃and 920℃）,atmosphere（different CH₄ content）and growth time（30 min,60 min and 90 min）on the growth of graphene were studied,The optimal growth conditions were obtained as follows:the growth temperature was 910℃,the growth atmosphere was argon:hydrogen:methane=250:10:3,and the growth time was 30 min.The results show that the graphene film grown on germanium substrate is single crystal structure,and the light transmittance of the graphene film at 270 nm is the lowest,which is 90.2%.In this paper,the dry transfer of graphene is realized by using heat release tape（TRT）.Compared with the graphene transferred by hydrogen bubbling method,the former has less impurities on the surface of graphene transferred to the target substrate.Finally,the growth theory of graphene is analyzed,and it is proved that the growth of graphene on germanium substrate is similar to the epitaxial growth of graphene on copper substrate.In this paper,the graphene/germanium photodetector is also constructed,and the photoelectric performance of the photodetector under visible light 550 nm and near-infrared light 1060 nm is studied,and the working mechanism of the photodetector is analyzed.In the study of 550 nm visible light,through the influence of light intensity density on photocurrent,the conclusion that photocurrent depends on light intensity density is obtained.Under the light intensity density of 10.23 m W/cm²,the responsivity and detectivity are as high as 28.15 m A/W and 6.7×10¹² Jones,respectively.The photoelectric performance of the device under different bias voltage was further studied under 550 nm visible light.When the bias voltage is-0.2 V,the maximum I_light/I_dark ratio is 4.03.In the study of near-infrared light at 1060 nm,it was also observed that the photocurrent increased with the increase of light intensity.The response time and recovery time are 0.41 s and 0.39 s,respectively.And the on/off ratio is 19.7.Under the illumination of 203.61 m W/cm²,the responsivity and detectivity are 4.5 m A/W and6.1×10¹¹ Jones,respectively.The external quantum efficiency of the device is calculated to be 531%.In this paper,we realized the growth of high-quality graphene film on germanium substrate,and explored the process of dry transfer of graphene using heat release tape（TRT）,which not only avoided the introduction of organic auxiliary transfer reagent,but also eliminated the safety risk of high-risk chemicals.The graphene/germanium photodetector can work normally under visible light and near-infrared light,which provides a new idea for realizing small high-performance devices in the process of optical chip integration.