Preparation Of Low Dimensional Semiconductor Heterojunction Nanomaterials And Their Application In Optoelectronics Devices

For more than half a century,the rapid development of integrated circuit technology has greatly promoted the progress of science and technology.At present,it has penetrated various fields of national production and human life.However,in the post-Moore era,if we want to keep the integrated circuit developing to a small size,and at the same time make the device computing speed constantly improve,this will put forward higher requirements on the semiconductor nanometer chip in the intelligent,integrated,miniaturization and other performance.Due to the unique electronic structure and quantum size effect,low-dimensional semiconductor heterojunction nanomaterials have the broad applications in photoelectric detection,field effect transistors,solar ce lls,and biosensing.At present,the research based on the novel low-dimensional semiconductor nanomaterials are at a rapid development stage,and a series of encouraging research results have been achieved.However,limited by the physical and chemical properties of single-component semiconductor nanomaterials,it is difficult to meet the practical requirements of the current multifunctional and high-performance integrated optoelectronic devices.Semiconductor nano-heterojunction,as a structure that can combine the performance advantages of two or multiple materials,breaks the performance limitations of single-component semiconductor nanomaterials.Especially,2D layered heterojunction materials as the representative structure,they can not be restricted by lattice matching,and any 2D materials with special performance can be combined,realizing the multi-function and high-quality optoelectronic devices.They are expected to break through the traditional silicon-based integrated circuit development bottleneck and will play a greater role in production and human life in the future.In view of this,this thesis focuses on the controllable fabrication of novel low-dimensional semiconductor heterojunction nanomaterials and the properties of micro-nano optoelectronic devices.Through the chemical vapor deposition method,a variety of new low-dimensional semiconductor heterojunction materials have been synthesized.Based on the space-time resolution pump detection technology,the carrier dynamics process inside the heterojunctions were studied and proved,and finally novel high-performance optoelectronic devices integrating with rectification and photovoltaic were realized.he main innovative research results of this paper are as follows:(1)High-performance two-dimensional p-n heterojunction photovoltaic devices.New two-dimensional Sb₂Te₃/MoS₂ vertically stacked p-n heterojunction nanosheets were fabricated through the two-step chemical vapor deposition method.As a p-n junction diode,the device has a significant rectification effect and the rectification ratio is as high as 1.2×10⁶.Under light condition,the Sb₂Te₃/MoS₂ p-n heterojunction nanosheets can be applied in photovoltaic devices,and their photoelectric conversion efficiency is as high as4.5%,which is much higher than that of most photovoltaic devices based on two-dimensional heterojunction nanomaterials synthesized by CVD method.Meanwhile,the p-n junction diode exhibits excellent photodetection performance:high photoresponsivity(330 A/W),high detection(10¹² J),and fast response time(360?s).The above results indicate that this novel p-n junction nanosheet has potential application in multifunctional and high-performance optoelectronic devices.(2)Self-powered broadband photodetector.Novel WSe₂/Bi₂Te₃ vertically stacked p-n heterojunction nanosheets were prepared.The results of microstructure characterizations conformed that the as-grown heterojunction nanosheets have high crystal quality.Furthermore,the p-n heterojunction nanosheet has excellent photovoltaic characteristics and photoelectric conversion performance.In addition,the absorption spectrum of the heterojunction material covers the range from visible light to near infrared light,and it show different levels of photovoltaic characteristics.based on this,high-performance self-powered broad-band photodetector has been constructed with the spectral detection range covering from 375 nm to 1550 nm.(3)High performance field effect transistor with adjustable Schottky barrier.Using van der Waals heteroepitaxial method,two-dimensional layered Bi₂Te₃nanosheets with high electron concentration and conductivity can be used as the contact electrodes to construct high mobility and low Schottky barrier MoS₂field effect transistor devices.The measurement results of the surface potential show that Bi₂Te₃ and MoS₂ have perfect band gap matching alignment.Based on this,ohmic contact can be formed after the Bi₂Te₃ and MoS₂ contact,which effectively reduces the contact barrier and makes it easy for carriers to cross the barrier and inject into the material.In addition,by changing the thickness of the two-dimensional Bi₂Te₃ nanosheet,thus changing its band gap and Fermi level,the tunable Schottky barrier height of the MoS₂ devices were achieved.Bi₂Te₃nanosheets as contact electrodes can effectively avoid the damage of the surface of two-dimensional semiconductor nanomaterials with atomic thickness by traditional micro-nano processing techniques.(4)According to the theoretical calculation results,different crystal planes of Cd S nanoribbons have different chemical activities.The chemical vapor deposition method with the mobile reaction source was adopted.By controlling the growth temperature of the reactants to achieve polar-induced selective crystal plane epitaxy growth.The as-grown lateral period Cd S/Cd S_xSe_1-xmulti-heterojunction nanoribbons have the continuous junction interfaces and the number of heterojunction interfaces can be tuned from 0 to 6.The results of microstructure characterization and optical characterization show that the as-grown multi-junction nanoribbons have atomically heterojunction interfaces.The measurement of the surface potential difference indicates that the junction interfaces ensure an efficient carrier transfer process.Photodetectors based on the lateral periodic multi-heterojunction nanoribbons also show excellent performance,and the photocurrent and photoresponsivity increase with the increasing number of heterojunction interfaces gradually.This lateral periodic multi-heterojunction nanoribbon will have the potential applications in electronic devices and optoelectronic devices.