The Preparation And Propreties Of Inorganic/Organic Thin Film Heterojunction Photodetectors

Novel Dirac quantum materials,including Dirac semimetals and topological insulators（TIs）,have become the focus of research in electronic materials science and photodetection in recent years.Cd₃As₂ is a typical representative of topological Dirac semimetallic material,which has linear dispersion relationship in three directions in momentum space and is also called three dimensional（3D）graphene.Meantime,due to the existence of the Dirac cone,the material has no optical band-gap,so it has the full band optical absorption and detection ability.The TIs,represented by bismuth telluride（Bi₂Te₃）and bismuth selenide（Bi₂Se₃）,are protected by the symmetry of time inversion and have excellent photoelectric properties.At present,Dirac materials have become an important carrier for the study of Majorana fermions and quantum anomaly/spin Hall effect in the field of basic research.The novel Dirac material has a wide application prospect in the field of photodetection because of its good optical absorption and photocurrent response characteristics.In this dissertation,the 3D Dirac semimetal Cd₃As₂ thin film and the bismuth-based second generation TIs Bi₂Te₃ and Bi₂Se₃ thin film are used as the research objects.By combining these thin film materials with other different types of materials,the thin film heterojunction photodetectors were prepared.In the experiment,the samples of Dirac thin films were prepared by molecular beam epitaxy（MBE）method,polymer thin films and organic small molecule thin films were prepared by spraying and thermal evaporation methods,respectively.The photoelectric properties of heterostructure devices were systematically studied.The research content of this dissertation can be summarized into the following six aspects:1.A photodetector based on pure 3D Dirac semimetal Cd₃As₂ thin film and bismuth-based Bi₂Te₃ thin film were prepared.The current responsivity（R_i）of Cd₃As₂ thin film photodetector was as high as 3.45 m A/W@650 nm and the maximum external quantum efficiency（EQE）was 2.39%.The R_i based on Bi₂Te₃ thin film photodetector was calculated to be 2.14 A/W and the maximum EQE was 65%（@650 nm）.Moreover,the absorption rates of Cd₃As₂and Bi₂Te₃ thin films were tested from ultraviolet to far infrared（200 nm～15000 nm）,laying a foundation for revealing the photoelectric response mechanism of the new materials.2.Based on the n-type 3D Dirac semimetal Cd₃As₂ and small molecule p-type organic Pentacene inorganic/organic thin film heterojunction photodetector was prepared.The device had an ultra-broadband response waveband（405 nm～10600 nm）,a R_i up to36.5 m A/W@650 nm and an EQE of 7.29%,and a device response speed of 30 ms was tested.Meantime,Schottky contact reverse inhibition and p-n junction contact characteristics were applied to reveal the photocurrent response mechanism of device.Hence,it lays a foundation for the prototype of low cost large linear devices.3.An inorganic/organic heterojunction photodetector composed of Cd₃As₂ thin film and PEDOT:PSS thin film was successfully fabricated.PEDOT:PSS film was prepared on Cd₃As₂ thin film by spraying method innovatively,which solved the problem that the surface of thin film was not easy to adsorb liquid material due to metal characteristics.The device had the capability of detecting from ultraviolet region to long-wave infrared region.The highest R_i,EQE,on-off ratio and device response time were 112 m A/W,23.4%,1123 and 282μs（@650 nm）,respectively.4.The 3D TIs Bi₂Te₃ and Pentacene thin film inorganic/organic heterojunction photodetector was prepared.The device had broadband response from 450 nm～3500 nm,the R_i,EQE and device response time up to 14.89 A/W,2840%,and 1.89 ms@650 nm.Meantime,the R_i of photodetector reached as high as 1.55 A/W@3500 nm.The device also had good flexible photoelectric performance and the corresponding photocurrent only changed less to 9.2%in a bending cycle.The photodetector and its preparation method had great application potential in the field of flexible photodetection.5.Based on 3D TIs Bi₂Te₃ thin film and small molecule p-type phthalocyanine organic matter（Cu Pc and Pb Pc）inorganic/organic thin film heterojunction photodetectors were prepared.These devices had excellent detection performance of polarized light and the maximum polarization coefficient can reach 2.56.It had a strong application prospect in the field of polarized light detection.Meantime,photodetectors had broadband response from 450 nm to 3500 nm,the R_i and EQE up to 23.54 A/W and4534%.Moreover,the devices processed response time of 1.42 ms and a R_i up to 1.93A/W@3500 nm.The above results indicate that Bi₂Te₃/Organics heterojunction devices are suitable for manufacturing high-performance IR optoelectronic components.6.3D TI/MoO₃ thin film heterojunction photodetector in optical communication waveband has been successfully prepared,which possessed ultrafast response time characteristic(τ_on=62μs,τ_off=73μs@1550 nm)with ultrahigh on-off ratio about 5.32×10⁴（@650 nm）.What’s beyond imagination is that the 3D TI/Mo O₃ thin film heterojunction device is with remarkable time stability performance（（29）100 days）without any protective measures at room temperature under atmospheric environment.Additionally,the maximum value of R_i of this type device could reach 1.6×10⁴ A/W（@405）nm with corresponding EQE as high as 4.9×10⁴%.Meanwhile,the detectivity（D*）of the device can up to 5.79×10¹¹ Jones@405 nm and 9.43×10¹⁰ Jones@1310 nm.Hence,the 3D TIs/Mo O₃ thin film heterojunction photodetector possesses excellent performance and offers a whole new approach to apply 3D TIs in optical communication detection field.To sum up,in this dissertation,the system based on 3D Dirac semimetal Cd₃As₂ thin film and the second generation of the TIs（Bi₂Te₃ and Bi₂Se₃）thin film materials combined with other types of thin film heterojunction photodetectors are preparated successfully,and study of different types of photoelectric device of flexible,polarization and array performance,and explore the working mechanisms of different types of detectors.These series of studies has important reference significance for the design of high-performance thin film heterojunction optoelectronic devices and the related working mechanism,and provides new research ideas and directions for the fabrication of flexible,polarized and array heterojunction optoelectronic devices.