Study On The Controlled Growth And Optoelectronic Device Applications Based On Organic/Inorganic Hybrid Van Der Waals Heterojunction

The past two decades have witnessed the rapid development of organic-inorganic heterostructures（OIHs）that have attracted great research enthusiasm due to their unique features for next-generation nanoelectronic and optoelectronic device applications.The as-fabricated OIHs are composed of organic rubrene(C₄₂H₂₈)and inorganic topological insulators（TIs）,namely Bi₂Se₃ and Bi₂Te₃.These heterostructure photodetectors（PDs）have several advantages such as low material cost,lightweight,less material consumption,low processing temperature,flexibility,and easy fabrication processing as compared to devices based on traditional materials.However,to realize their practical applications,a series of challenges still need to be overcome.One of the primary challenges is the preparation of these heterostructures using high-cost and high-maintenance methods such as the molecular beam epitaxy（MBE）.The second issue is the large dark currents generation,energy band alignment,and internal dynamics of these TIs-based OIHs,which require further investigation.Therefore,this work focuses on the design and fabrication of low-cost OIHs with excellent diode behaviors,to reduce the dark currents,and improve their specific characteristics.Recently,TIs constitute a novel class of quantum materials in condensed matter physics.These materials are different from normal semiconductors in the sense that they have insulating bulk and conducting surface states.These surface states are formed as a result of strong spin-orbit coupling（SOC）and time-reversal symmetry（TRS）,topologically protected against any external perturbations such as non-magnetic impurities and small lattice defects.The family of TIs is growing rapidly with Bi₂Se₃,Bi₂Te₃,Bi₂S₃,and Sb₂Te₃ compounds predicted as the strong3D TIs being confirmed theoretically as well as experimentally.Among them,Bi₂Se₃ and Bi₂Te₃have drawn much attention due to their small bandgaps and intriguing optical and electrical properties.In addition,various organic semiconductors have been explored for the development of novel low-cost and high-stability devices for practical applications.Among these,the single crystalline rubrene is one of the most promising candidates due to its highest mobility of～40cm²/V·s and long excitonic diffusion length of～2-8μm.These properties make rubrene a superstar in organic semiconductors,well-suited for fabricating high-quality heterostructures.In this dissertation,the controlled growth,processing,and characterization of PDs based on OIHs were investigated.All the heterostructures were prepared via a simple two-step physical vapor deposition（PVD）approach.The structural quality and surface morphologies of the grown heterostructures and electrical and optical characterization of devices were systematically studied using different characterization techniques.The results showed that the devices we prepared combined the advantages of organic rubrene and inorganic TIs,Bi₂Se₃ and Bi₂Te₃,and improved the characteristic parameters of the device.Therefore,the purpose of this research work is to investigate the surface,physical,and electrical characteristics of the materials and OIHs system,establish appropriate device designs,and experimentally construct PDs that outperform presently available devices.The research content mainly reports the following two aspects:1.Organic-inorganic heterojunction photodetector Rubrene/Bi₂Se₃/SiO₂Firstly,a high-performance organic/inorganic hybrid vd Ws heterostructure PDs rubrene/Bi₂Se₃/SiO₂ was demonstrated by integrating the n-type TI Bi₂Se₃ as the inorganic active layer and p-type rubrene as the organic component by employing a simple two-step PVD technique.The PVD technique is very beneficial to the vd W epitaxial growth of highly ordered and crystalline OIHs due to the dangling bonds-free and no charge trap states on the surface of vd W substrates.The as-fabricated device displays a high responsivity of 8.85 AW^-1,a high detectivity of 3.14×10¹² Jones,and an ultrafast response speed with a rise time of 2.1μs and a decay time of 2.9μs under light illumination of 1064 nm.These excellent device performance parameters are attributed to the formation of efficient organic-inorganic heterojunction and Ohmic contacts.This study discusses the hybridization of organic-inorganic materials to construct heterostructures,which have promising applications for photodetection in electronic and optoelectronic devices.2.Organic-inorganic heterojunction flexible photodetector Rubrene/Bi₂Te₃/MicaSecondly,employing the same two-step PVD approach another high-performance rubrene/Bi₂Te₃/Mica heterojunction flexible PDs using the p-type TI Bi₂Te₃ as the inorganic material and p-type rubrene as the organic material was established.This newly-designed device revealed excellent diode behaviors and significantly enhanced photoresponse characteristics in a self-powered mode with an I_on/I_off ratio of 6.2×10⁴.The device shows a high responsivity of852.7 AW^-1,a high detectivity of 1.42×10¹³ Jones,and an ultrafast response speed withτ_r of 14μs andτ_d of 16.2μs under 1064 nm light irradiation.Due to these outstanding results,this newly-developed OIHPD is anticipated to open up new potential opportunities in multifunctional device applications.The as-fabricated devices showed a broadband photodetection ranging from UV to NIR wavelengths.Furthermore,the Dirac surface state at the rubrene/TIs heterojunction interface greatly facilitates the dissociation as well as transportation of photo-generated carriers,resulting in superior photoelectric characteristics of the device’s NIR light illumination of 1064 nm.Thus the proposed work enables the utilization of these OIHPDs as a self-powered device in low energy consumption optoelectronics and suggests a potential opportunity for novel multifunctional devices.In summary,further improvement is expected after the device architecture optimization and the development of new growth approaches,to provide a platform for constructing high-performance OIHPDs for next-generation NIR photodetection applications in the future.