ZnO压敏陶瓷晶界势垒高度和宽度的研究

通过测量商用ZnO压敏陶瓷材料的泄漏电流I与绝对温度T,并利用场助热激发电流的表达式计算了势垒高度(活化能),发现它低于平衡状态时的势垒高度。在深入分析在电场作用下晶界区域中电子传导过程的基础上,认为这是在电导过程中通过正偏势垒向晶界界面层中注入了大量电子,这些电子不仅填充了在平衡状态下尚未填充的电子陷阱(即表面态),而且还会在界面层形成自由电子空间电荷,这些自由电子在越过反偏Schottky势垒时需要克服的就不是平衡状态时的势垒高度,显然应低于平衡状态时的势垒高度,即导带底EC的最高点与费米能级Ef的差值(通常势垒高度的定义)。另外,根据场助热激发电流的表达式,提出了新的Schottky势垒宽度的计算公式,不仅求得了高场强和低场强时的势垒宽度,而且得到了势垒宽度随温度的变化规律,发现了在320K～350K温度范围内势垒宽度下降速度最快,结合介电温谱测量,证实了在此温度区间势垒宽度的快速下降是松弛过程引起的。

Research of Barrier Height and Width in ZnO Varistor Ceramics

Based on the measurement of the relation between the leakage current I and absolute temperature T in commercial ZnO varistor ceramic samples,the barrier height(activation energy)was estimated in the presence of the expression of field enhanced thermal emission current and was found to be lower than barrier height on the balanced state.After lucubrated the process of electron conduction in the grain boundary region under electric field,we pointed out that in the conduction process a lot of electrons will be injected into interfacial layer through forward-biased barrier,the electrons would both fill electron traps(surface state)remained emptied on the balanced state and form free electron space charge in interfacial layer,then these free electrons just need overcome a potential height lower than that one on the balanced state,that is the difference between the climax of the conduction band(E-C)and Fermi energy lever(E-f).Moreover,we presented a new expression to Schottky barrier width according to the expression of field enhanced thermal emission current,both the barrier width at high and low field and the variation law between the barrier width and temperature can be got.We found barrier width has fell most rapidly in the range of 320K to 350K and proved it resulted from the relaxation process according to the measurement of dielectric spectroscopy.