ZnO/MgO核壳纳米线的可控合成及高性能紫外光电探测器研究

In order to solve the problems that ZnO nanowire based UV photodetector presented large noise dark current and low on-off ratio, this project propose a ZnO/MgO core/shell nanowire based Metal-Insulator-Semiconductor (MIS) Schottky diode photodetector. By using the MgO insulator layer to increase the eneggrgy barrier, passivate the surface defect states, and reduce the dark current, increse the on-off ratio. First, according to the Vapor-Liquid-Solid (VLS) mechanism, the ZnO core and MgO shell can be synthesized in one step and formed high quality interface, which aviods the large number of defects and low interfacial quality in conventional methods that grew MgO shell in second step. Then, the MIS photodetector was fabrcated by focused ion beam method. the carrier transportation mechanism of the MIS junction was approved according to the heterjunction energy band model, the thermal emission and tunneling theories. the carrier transportation rule and response mechanism during the phororesponse was analysized, the influence of MgO thichness, the applied bias voltage on photoresponse performance was studied. and finally the high-performance ZnO nanowire MIS UV photodetector was fabricated. this work can be used to fabricate high-performance UV photodetector in micro and nanoscale, and can be used in missle warning and fire alarm.

本课题针对ZnO纳米线紫外光电探测器噪声暗电流大、开关比低的问题，提出制备基于ZnO/MgO核壳纳米线的“金属-绝缘体-半导体”（MIS）结型紫外光电探测器，利用插入MgO绝缘层的方法来提高能带势垒、钝化表面态，从而降低器件暗电流，提高开关比。研究中首先根据纳米线的“气-液-固”形核机理，采用单步化学气相沉积法同时生长ZnO纳米线和MgO壳层，避免了二次沉积MgO壳层所导致的缺陷多，质量差的难题。然后利用聚焦离子束技术制备单根ZnO/MgO核壳纳米线MIS结型紫外光电探测器。并根据异质结能带模型，结合载流子热发射理论和隧穿理论，阐明MIS结的载流子输运机制，分析光响应过程中载流子运动规律和响应机理，研究了MgO壳层厚度、外加电压等对光响应性能的影响规律，并制备出高性能ZnO纳米线MIS结紫外光电探测器。本研究可用于制备微纳米高性能紫外光电探测器，在导弹预警、火焰探测等领域具有应用价值。

ZnO纳米线具有禁带宽、室温激子束缚能高等优点，可用于制备高性能紫外光电探测器，在导弹追踪、电晕监测、火灾预警等领域具有重要的应用价值。然而，p型ZnO的制备一直制约着ZnO基光电器件的发展，基于其它p型衬底与ZnO组成异质PN结，就成了很好的备选方案。本项目选择p-Si和p-GaN两种p型衬底与ZnO构筑异质PN结，分别实现了光探测器和发光二极管。基于此，本项目主要开展如下3方面的工作：1、溶液法合成ZnO纳米线阵列，首先研究了合成工艺参数如种子层厚度、PEI添加剂等参数对ZnO纳米线形貌的影响规律，并分析了退火温度、退火气氛等参数对纳米线荧光性能的影响机理。2、设计并制备了ZnO纳米线/p-Si异质结紫外光电探测器，通过在生长液中添加PEI，显著降低了材料的杂质密度，减小了异质结二极管的反偏暗电流，提高了器件的光响应性能。3、设计并制备了ZnO纳米线/p-GaN异质结，利用二者的晶格失配小，带隙宽度接近等性能，形成高质量异质PN结，并成功实现发光二极管。测试表明该器件在正偏和反偏下都能发光，通过高斯分峰拟合对其反偏电致发光光谱分析，并结合异质结能带理论表明反偏发光光谱多由界面处的深能级缺陷态所产生。本项目的成果可为ZnO纳米线光电器件的研究提供参考。