新型日盲紫外探测器AlGaN光电阴极材料生长关键技术研究

As a direct band-gap material, ternary nitride alloy AlGaN has a tunable energy ban-gap from 3.4 eV to 6.2 eV as Al content increasing, which covers the ultraviolet wavelength from 365 to 200nm. It is a very promising material for a number of applications in ultraviolet (UV) detector devices, such as flame sensing, missile warning, UV biological effects, UV astronomy and space-to-space communication. With the advantages of high sensitivity, small dark emission, high quantum-efficiency（QE） emission, and high solar blind response the negative electron affinity(NEA)AlGaN ultraviolet photocathode is an ideal ultraviolet photocathode. For The lack of lattice-matched substrates, AlGaN photocathode has usually been fabricated on foreign sapphire substrates and grown by metal-organic chemical vapour deposition (MOCVD). In order to realize high-efficiency photocathode, it is crucial to obtain a highly conductive p-type AlGaN layer with low defects density. Unfortunately, this is very difficult due to the larger acceptor ionization energy and lower formation energy of compensation defects in the material with higher Al mole fraction. Typically, the activation energy of an Mg acceptor in AlGaN alloys rises from 160 meV to 500 meV with increasing Al mole fraction x from 0 to 1. A nitrogen vacancy which acts as a compensation center has low formation energy, which became smaller with increasing Al mole fraction. In this subject, it is focused on the growth of low defects density and low resistivity value p-type AlGaN emission layers with high-Al content values over 0.4. In order to devise NEA AlGaN ultraviolet photocathode with high QE and high solar blind response, the intrinsic band structure of AlGaN buffer with Al mole fraction decreasing from 1 to 0.4 and the depth grade doping photocathodes will be investigated at first. To improve the crystalline quality of AlGaN emission layers grown on sapphire, we will introduce a pulsed atomic-layer epitaxial (PALE) AlN as the buffer layer for the photocathode epilayer. And the influence of the growth condition on the crystal growth modes for the PALE AlN will be studied carefully. For the growth low resistivity value of p-type AlGaN epilayer with a high Al content, we propose a TMIn-assistant method in this subject. And the influence of this method on the Mg doping concentration will be investigated. Moreover, to reveal the mechanism of the in situ anneal method in improving the QE of the photocathode, the formation and control process of acceptor compensation defects will also be studied in this subject. Finally, a method of growing low defects density and low resistivity value AlGaN photocathode epilayers by MOCVD will be obtained, which is the base of preparation for solar blind UV detectors with high spectral response.

AlGaN材料其禁带宽度可以随着铝组分连续变化，对应的波长从365 nm变化到200 nm，是制作日盲紫外探测器的理想材料，可实现高度选择性日盲紫外探测。当前制约AlGaN光电阴极在紫外探测技术上应用的最大障碍是低缺陷密度、低电阻率光电阴极材料的制备。本课题以外延生长高质量AlGaN光电阴极材料为目标，主要开展以下工作：基于渐变组分AlGaN过渡层和梯度掺杂发射层等结构，通过理论计算和能带剪裁，设计日盲紫外AlGaN光电阴极结构；采用MOCVD技术外延生长光电阴极材料，研究脉冲原子层外延方法中材料成核生长机理，分析外延工艺参数对生长模式的影响，通过生长模式的调控来制备高质量阴极材料；研究Mg-In共掺的方法对阴极材料Mg掺杂效率和激活效率的影响；研究阴极材料中受主补偿中心的形成和控制，揭示原位退火技术提高光电阴极量子效率的作用机理，获得一种制备低缺陷密度、低电阻率AlGaN光电阴极材料。

AlGaN材料其禁带宽度可以随着铝组分连续变化，对应的波长从365 nm变化到200 nm，是制作日盲紫外探测器的理想材料，可实现高度选择性日盲紫外探测。当前制约AlGaN光电阴极在紫外探测技术上应用的最大障碍是低缺陷密度、低电阻率光电阴极材料的制备。本课题以外延生长高质量AlGaN光电阴极材料为目标，主要开展了以下工作：基于渐变组分AlGaN过渡层和梯度掺杂发射层等结构, 通过理论计算和能带剪裁，设计日盲型紫外AlGaN光电阴极结构；采用MOCVD技术外延生长光电阴极材料，研究脉冲原子层外延方法中材料成核生长机理，分析外延工艺参数对生长模式的影响，通过生长模式的调控来制备高质量阴极材料；研究Mg-In共掺的方法对阴极材料Mg掺杂效率和激活效率的影响；研究阴极材料中受主补偿中心的形成和控制，揭示原位退火技术提高光电阴极空穴浓度的作用机理，掌握了制备低缺陷密度、低电阻率AlGaN光电阴极材料的外延生长关键技术，外延获得了空穴浓度高达2.3E17/cm3的AlGaN光电阴极材料，研制成功了高灵敏度AlGaN紫外日盲光电阴极。