Research On VIS-NIR Detectors Based On Low-Dimensional Bi₂O₂Se Nanocrystals

Infrared（IR）detectors have broad applications in astronomy,military,medical,security and modern industrial detection.The next generation of infrared detectors is advancing towards higher performance,lower power consumption,smaller size,lower cost and more informatization.Currently,two-dimensional materials are regarded as promising platforms for next-generation electronic and optoelectronic devices owing to their unique physicochemical properties.However,they still fail to satisfy the demands of suitable bandgap,high carrier mobility and good environmental stability in the detection of visible to near-infrared（VIS-NIR）bands.In this context,two-dimensional bismuth oxyselenide（Bi₂O₂Se）exhibits excellent environmental stability,high conductivity and non-toxicity,rendering it a superior candidate material for VIS-NIR band detection.Nevertheless,Bi₂O₂Se-based detectors suffer from large dark current and slow response speed in the NIR band,which are attributed to its high carrier concentration and bolometric effect.To address these issues,previous studies have attempted to suppress the dark current by gate voltage,but extremely high gate voltage will augment the power consumption of the device.Hence,this thesis employs a nanoribbon structure of appropriate width and a method of constructing a van der Waals heterojunction to diminish the dark current of the Bi₂O₂Se-based detector and enhance the response speed of the device,achieving high-performance detection in the VIS-NIR bands.The specific researches of this thesis are as follows:（1）Bi₂O₂Se nanocrystals with different widths were grown on fluorophlogopite by chemical vapor deposition（CVD）,and the lateral widths were regulated by growth parameters in the range of 38 nm to 200μm.Based on four kinds of nanocrystals with different widths（same thickness）,photoconductive detectors with the same channel length were prepared,and the relationship between the crystal width on the dark current and the on-off ratio of the device was studied.It is proved that the nanoribbon structure is the preferred solution to achieve higher detection performance.（2）The structure of the nanoribbon detector was optimized,and an asymmetric Schottky barrier was introduced in the Au/Bi₂O₂Se nanoribbon/Au structure to which suppress the dark current of the device to the order level of 10^-8 A,The detection band was 405-2250 nm and the response time was op to～2.1μs at the wavelength range of the650-980 nm band and～300μs at the wavelength range of the 1310-1550 nm band,and the maximum responsivity and specific detectivity reached 3.27×10⁵ A W^-1and 3.28×10¹³Jones,respectively,which are better than superior to the currently reported Bi₂O₂Se photoconductive detectors.（3）Bi₂O₂Se/Hf S₂ van der Waals heterojunctions were constructed,and the interlayer coupling effect and large junction potential barriers were verified by Raman spectroscopy and ultraviolet photoelectron spectroscopy.The dark current is further suppressed to the order level of 10^-11 A with a rectification ratio of 59。The on/off ratio of device reached3.8×10³ at V_ds=-5 V.The detection wavelength rang is 405-1310 nm,and the maximum responsivity reached a maximum value of 499.9 m A W^-1,which is competitive among the heterojunction-type detectors based on Bi₂O₂Se.