Li Huanglong, Robertson John
Department of Precision Instrument, Center for Brain Inspired Computing Research, Tsinghua University, Beijing, 100084, China.
Engineering Department, University of Cambridge, Cambridge, CB2 1PZ, UK.
Sci Rep. 2019 Feb 12;9(1):1867. doi: 10.1038/s41598-018-37717-x.
The electronic structure and conduction mechanism of chalcogenide-based Ovonic threshold switches (OTS) used as selectors in cross-point memory arrays is derived from density functional calculations and quasi-Fermi level models. The switching mechanism in OTS is primarily electronic. This uses a specific electronic structure, with a wide tail of localized states below the conduction band edge. In amorphous GeSe the conduction band consists of Ge-Se σstates with a low effective mass, and with a broad tail of localized Ge-Ge σ states below this band edge. This leads to the OTS behavior. At high fields the electron quasi-E moves up through these tail states, lowering the conductivity activation energy, and giving the non-linear switching process. The 4:2 coordinated GeSe based alloys are the most favorable OTS material because they have the correct network connectivity to give a high electron mobility and lack of crystallization, a favorable band structure to produce the non-linear conduction, an optimum band gap, and with nitrogen or carbon alloying, a sufficiently low off-current.
用作交叉点存储阵列中选择器的硫族化物基奥氏阈值开关（OTS）的电子结构和传导机制源自密度泛函计算和准费米能级模型。OTS中的开关机制主要是电子性的。这利用了一种特定的电子结构，在导带边缘下方有一个宽的局域态尾部。在非晶态GeSe中，导带由具有低有效质量的Ge-Se σ态组成，并且在该带边缘下方有一个宽的局域Ge-Ge σ态尾部。这导致了OTS行为。在高场下，电子准能级E向上穿过这些尾部态，降低了电导率激活能，并给出了非线性开关过程。基于4:2配位的GeSe合金是最有利的OTS材料，因为它们具有正确的网络连通性以提供高电子迁移率且缺乏结晶，具有产生非线性传导的有利能带结构、最佳带隙，并且通过氮或碳合金化，具有足够低的关断电流。
