隧穿场效应晶体管中齐纳隧穿的理论研究

The tunneling field-effect transistor has received tremendous attentions due to its potential to reduce the power consumption by decreasing the supply voltage and to overcome the subthreshold swings limitation of 60 mV/decade at room temperature for traditional Metal-Oxide-Semiconductor transistors. However, it is still insufficient about the research of the working principle of tunneling field-effect transistor and how to improve the performance of the device. Based on density fuctional theory, we will investigate the physical mechanism of Zener tunneling in the tunneling field-effect transistor by using the plane-wave non-local pseudopotential method. By analyzing the scattering state of electron, we also hope to understand how a electron transforms from the valence band-like properties to the conduction band-like properties. The process of the electrons from the valence band tunnel through the band gap to the conduction band will be described clearly. According to the results obtained, we will develop a general formalism for band-to-band tunneling by combining the traditional effective mass and K.P method. Then the tunnel field-effect transistors will be simulated accurately by using this corrected method. Trap assisted tunneling is an important aspect of experimental tunnel field-effect transistors, which are today the most promising devices for next-generation low-power transistors. A fundamental understanding of the mechanism of trap assisted tunneling is need. We will disscuss the physical properties of the impurities and defects in the channel region by the detailed ab initio calculation. The effect of trap location, trap energy and trap density on on-current and subthreshold swings (SS) will be studied in detail. An accurate electron-phonon interaction for semiconductor compound material will be obtained to discuss phonon-assisted band to band tunneling. We will find a framework to calculate the current due to phonon-assisted tunneling in indirect semiconductors. We believe that our results will be helpful to optimize the tunneling field-effect transistors design and develop the new devices.

由于隧穿场效应晶体管在降低能耗、突破亚阈值摆幅限制等方面的优势，受到广泛关注。然而，对于理解器件的物理本质和提高器件性能方面的研究尚不充分。本项目拟从密度泛函理论出发，采用非局域平面波赝势方法，探讨隧穿场效应晶体管器件中Zener隧穿的物理本质，通过分析散射态，正确理解电子从价带性质向导带性质的转化，获得电子波矢在带隙中的转变途径，利用所得结论，对传统基于有效质量近似的WKB方法和k.p方法作合理修正，利用修正后模型对隧穿场效应晶体管进行模拟。通过ab initio计算，细致讨论沟道区杂质和缺陷的物理性质，获得陷阱态辅助隧穿的机理，讨论杂质与缺陷位置和浓度对器件开启电流和亚阈值幅摆的影响。深入分析材料声子模特性，对合金半导体材料获得较准确的电子-声子相互作用，结合传统处理电子跃迁的方法研究声子辅助带间隧穿。以期解释和预言新物理现象，推动隧穿场效应晶体的优化设计，指导新型半导体器件的研制。

传统硅基晶体管尺寸微缩（摩尔定律）带来的短沟道效应造成了集成电路功耗的增加，因此需要设计和实现使用功能驱动替代密度驱动的新型（新材料，新原理，新结构）晶体管。基于量子力学原理的隧穿场效应晶体管（TFET）因具有陡峭的亚阈值摆幅（SS）和较小的关态漏电流已经成为当下取代金属氧化物半导体场效应晶体管 (MOSFET) 的候选者之一。但是，关于TFET隧穿机制中声子和缺陷对电子输运特性影响的研究尚不完善，且量子效应的引入使得计算晶体管输运性质的半经典方法受到制约。因此，本项目采用密度泛函和非平衡格林函数相结合的第一性原理量子输运方法，对基于有效质量近似的WKB方法和k.p方法进行了合理修正，给出了WKB模型存在误差的原因。并利用修正后的转移矩阵模型和费米黄金规则方法分别研究了直接带隙和间接带隙半导体中通过缺陷势阱的声子辅助隧穿机理，讨论了三维硅中声子模式、温度以及缺陷位置、缺陷势阱的深度、缺陷浓度等物理参数对隧穿电流和器件性能的影响。为了进一步提升TFET的开态电流和开关斜率，项目将具有高迁移率、适中带隙的低维层状半导体作为研究对象，通过应变、钝化、吸附等方式对二硫化钼、黑磷、ZnSe、GeP、In-V族和范德华异质结等材料的电子结构性质进行了探索性地调控，揭示了原子细节问题与电子隧穿的关系，在此基础上构筑了器件结构并实现了其在亚10 nm器件沟道中的应用。最后运用严格的第一性原理输运方法从原子尺度对二极管和双栅TFET的非弹性输出特性以及转移特性曲线进行了仿真模拟。本项目研究成果对场效应晶体管、尤其隧穿场效应晶体管的基础实验研究和器件研制具有重要的价值。