过掺杂补偿缺陷与异质结能级对纳米ZnO气敏特性调节机制的研究

The developed physical model,also D-2L model, to elucidate the interactive mechanism of chemical gas-sending devices is limited to corralate the MOS intrinsic defects and/or the compensating defects by substitutive ion-doping to the MOS gas-sensing performance, and still inefficient to solve and prodict the case dominated by ion-overdoping defects and the hetero-interface energy-levels..Choosing nano-ZnO as objective, and the relatiionship of the ion-overdoping, hetero-junction and conductivity of MOS thin films and their interactive synergicity, as pointcut, this present project strives to elaborate the compensating defect-dependent electronic depletion layer thickness, by systematically investigating the influences of compensating types and carrier concentration on the ZnO conductivity and the corresponding gas-sensing performance. Furthermore, it is to found out the underlying relationship of defect- electronic-gas sensing properties of MOS film, especially nano-ZnO. As more important and indispensible part, the present project is also to uncover the interface energy-level-determined electronic depletion layer by designing core-shell hetero-structured ZnO based nanoparticles as sensing elements and carfully investigating the conductivity and the related gas-sensing propertis of various hetero-structured core-shell ZnO, in order to deeply manifest the underlying mechanism of hetero-interface energy-level moderating gas-sensing of hetero-structured ZnO-based chemical sensors. Finally, generalized the above two aspects, this current proposal is to establish more systematically the controllable gas-sensing mechanism and model, especially in ZnO-based chemical sensors.

现有化学气敏传感器的物理机制（D-2L模型）局限于MOS本征或替代式离子掺杂的缺陷态与气敏特性的关联，尚未有效地解决过掺杂及异质结构对MOS气敏性能的作用机制问题。本项目以纳米ZnO为对象，以过掺杂、异质结效应与ZnO薄膜电学性质的关系及两者之间的协同性为切入点，分别考察离子过掺杂ZnO的缺陷类型、浓度与薄膜电学性质、气敏特性的关系，确定过掺杂对纳米ZnO气固界面电子耗散层厚度的控制规律，建立ZnO薄膜的补偿缺陷类型及浓度-电学性质-气敏性能之间的内在关联；通过材料结构设计，分别考察不同类型核/壳型ZnO异质结的能级结构与薄膜电学性质、气敏性能之间的关系，确定异质结的能级结构对本体ZnO的电子耗散层厚度的控制规律以及与薄膜气敏性能之间的内在关联性。在上述基础上，形成更为系统的ZnO基气敏传感器的气敏性能调节机制模型。

本项目围绕纳米ZnO的表面缺陷及异质结的能级结构，分别研究了掺杂纳米ZnO的补偿缺陷与气敏薄膜的导电率与气敏性能的关联性、两类异质结纳米ZnO的界面能级及对气敏薄膜导电性与气敏薄膜的调控机制。证实了施主缺陷、掺杂离子价态与离子半径对纳米ZnO气敏薄膜的调控规律影响；确定了金属-ZnO异质界面处电子的转移及界面Schottky能垒高度对薄膜气敏特性的调制规律；发现了氧化物-ZnO纳米异质结的N-P-N型气敏导电转变现象，并提出了Type-II型能带结构决定的电荷分离引起气敏导电类型转变的新气敏机制。本项目所发展的纳米ZnO气敏性能调控方法及材料制备技术，在发展低浓度VOC环境污染气体检测、报警传感器有理论参考价值与实际应用价值。.主要结论与研究成果如下：.（1）确定了制约纯相纳米ZnO的气敏特性的关键因素是ZnO颗粒表面施主缺陷，即反位氧缺陷与单电子氧空位；而掺杂离子对ZnO的缺陷类型与相对含量、导电性及气敏性能的作用复杂：离子半径相近，低价离子掺杂增加施主型缺陷，提高气敏性能；高价掺杂引起电子补偿，气敏性能变差；当离子半径相差较大，离子填隙缺陷起决定性作用；若补偿缺陷主要是施主型缺陷（低价掺杂），填隙缺陷束缚电子，降低气敏性能；若补偿缺陷为电子补偿（高价掺杂），填隙缺陷抑制电子-空穴，增强气敏性能。.（2）证实了金属-ZnO纳米异质结气敏性能表现出对金属侧功函数的依赖性，功函数越大，对ZnO导带的拉电子能力越强，界面Schotty能垒越高，气敏性越强；通过构建金属-金属异质结来调控金属-ZnO异质结金属侧的Schottky能垒。复合金属的功函数越高，复合金属-ZnO异质纳米颗粒的气敏性越高。.（3）首次发现N-N型氧化物-ZnO异质结纳米材料气敏材料在检测低浓度VOCs时的N-P-N导电转换特性，提出了异质结Type-II 能级特征导致“类电容”的电荷分离引起N-P-N导电类型转变新的气敏机理。.（4）项目执行期间，公开发表SCI论文11篇，提交论文3篇；申请国家发明专利1件；参加国际会议并做学术报告一次，培养学生2名。