基于电场分布调控的高增益ZnO肖特基型紫外雪崩探测器研究

Avalanche photodetector is the ideal choice for detecting weak ultraviolet signal. For ZnO thin film material, there is only one report about ZnO ultraviolet avalanche photodetector with Au/MgO/ZnO/MgO/Au double Schottky structure which is constructed by the applicant in the previous work. Although the good experimental results have been achieved in the device, the multiplication gain of device is too low. Aiming at the problem, the project will achieve high gain of ZnO ultraviolet avalanche photodetector on the basis of previous work, which is realized by the regulation and control of electric field distribution within device. Namely, the project will confine the electric field of device in the multiplication layer by optimizing the device structure to achieve high multiplication gain. Firstly, the project will focus the voltage of device on the reverse biased Au/MgO/ZnO Schottky barrier, which is realized by replacing the double Schottky structure in the previous work with the Au/MgO/ZnO/Al single Schottky structure. Secondly, the project will focus the voltage of the reverse biased Au/MgO/ZnO Schottky barrier on the MgO insulator layer (multiplication layer) by means of the improvement of ZnO film conductivity, which is achieved by the enhancement in incident light absorption of ZnO film realized by localized surface plasmon resonance of Ag nanoparticles. The electric field of device will be confined in the multiplication layer through the above two-step regulation and control. So the project is expected to achieve ZnO ultraviolet avalanche photodetector with high gain in the Au/MgO/ZnO/Al structure decorated by Ag nanoparticles.

雪崩光电探测器是探测微弱紫外信号的理想选择。对于ZnO薄膜材料，目前已报道的只有申请者在前期工作中制备的Au/MgO/ZnO/MgO/Au双肖特基结构的ZnO紫外雪崩探测器。该器件虽取得了较好的实验结果，却存在着倍增因子过低的问题。针对这一问题，本项目拟在前期工作的基础上，通过调控器件内电场分布（即优化器件结构，将电场限定在倍增层）来实现器件高增益。本项目拟用Au/MgO/ZnO/Al单肖特基结构代替前期工作中的双肖特基结构，这便将器件内电压首先集中在反向偏置的Au/MgO/ZnO肖特基势垒上；拟利用Ag纳米颗粒的局域表面等离子体共振增强ZnO层对入射紫外光吸收，进而大幅度提高其电导率，从而将反向偏置的肖特基势垒上的电压进一步集中在MgO介电层（倍增层）。以上两步调控实现了电场限定在倍增层，因此本项目有望利用Ag纳米颗粒修饰的Au/MgO/ZnO/Al结构实现高增益的ZnO紫外雪崩探测器。

为了实现能够探测微弱紫外信号的高增益ZnO紫外雪崩探测器，本项目构建了Ag纳米颗粒修饰的Au/MgO/ZnO/Al单肖特基结构的ZnO紫外雪崩探测器。当器件两端施加反向偏压时，器件内电压首先集中在反向偏置的Au/MgO/ZnO肖特基势垒上。当380nm波长紫外光照射到ZnO表面覆盖的Ag纳米颗粒上时，会产生局域表面等离子体共振效应，这会增强ZnO层对入射紫外光吸收，进而大幅度提高ZnO层电导率，从而将反向偏置的Au/MgO/ZnO肖特基势垒上的电压进一步集中在MgO介电层（倍增层）。以上两步电场分布调控实现了器件内电场限定在MgO倍增层，从而有利于在倍增层中实现高电场。由于高电场能够实现载流子的高雪崩增益，因此在该结构中能够实现高增益的ZnO紫外雪崩探测器。在众多该结构的ZnO紫外雪崩探测器中，性能最为稳定的器件的雪崩阈值电压仅为15V, 这是目前已知的ZnO薄膜紫外雪崩探测器最小雪崩阈值电压。该器件在21V电压下实现了其最高雪崩增益，其雪崩倍增因子为78，这是已知的ZnO薄膜紫外雪崩探测器在该偏压下最高雪崩倍增因子。因此，本项目达到了基于电场分布调控的物理思想，在低电压下实现高增益ZnO紫外雪崩探测器的目的。