Current Instability and Gunn Effect in Two-Dimensional Systems

本项目的目的是研究短沟道场效应晶体管中的非线性输运现象。最近，Dyakonov和Shur发现电子流体在二维通道中的流动应该是不稳定的。这种不稳定性导致在太赫兹频率范围内产生等离子体波。因此，人们提出了一种新型的太赫兹器件(振荡器、探测器、混频器)，并展示了一种太赫兹场效应晶体管探测器。我们将研究由不稳定性的发展引起的平稳非线性振荡。由不稳定性引起的冲击波的形状、幅度和速度将考虑电子-电子散射引起的电子流体的粘性以及与声子和杂质散射有关的外摩擦力来计算。将分析结果与数值计算结果进行比较。该理论还将描述基于短沟道场效应晶体管的太赫兹辐射探测器的非线性工作状态。这种不稳定性也将在电子密度较小的情况下进行研究，当电子-电子碰撞可以忽略时(无碰撞等离子体)。找出了无碰撞等离子体的不稳定性条件。不稳定的线性区域也将被考虑。他们研究的另一个主题是二维系统中的一种所谓的“失控”效应，它导致了负微分电阻。他们的初步估计表明，与三维情况相反，即使是形变的光学和声学声子散射，也会发生这种失控。在基于硅(锗)的2D系统中，这将导致负的微分迁移率。该项目的主要任务之一是研究在2D Si(Ge)MOS结构中产生耿氏效应的可能性。我们将研究二维场效应晶体管沟道中负微分的后果。这种情况与传统的三维Gunn效应有很大的不同，因为扩散非指数定律支配着二维FET沟道中的电荷弛豫。电子-电子相互作用在二维“失控”中的作用也将被研究。

0080509ShurThe purpose of the proposed project is to study the non-linear transport phenomena in short - channel Field Effect Transistors. Recently Dyakonov and Shur have discovered that flow of the electron fluid in two-dimensional channel should be unstable. This instability results in plasma wave generation in a terahertz frequency range. As a consequence, the novel terahertz devices (oscillator, detector, mixer) were proposed, and a terahertz FET detector has been demonstrated.A strong non-linear regime of this instability in a ballistic field effect transistor will be studied. The stationary non-linear oscillations resulting from development of the instability will be investigated. The shape, amplitude, and velocity of the shock waves caused by the instability will be calculated taking into account the viscosity of the electron fluid due to electron-electron scattering and the external friction related to the scattering by phonons and impurities. The analytical results will be compared with the numerical calculation. This theory will also describe a non-linear regime of operation of a terahertz radiation detector based on the short-channel field effect transistor. This instability will also be studied in the case of small electron densities when the electron-electron collisions can be neglected (collisionless plasma). The conditions of the instability for collisionless plasma will be found. The linear regime of the instability will be also considered. The resonant frequencies of oscillations and the increment of instability will be calculated.Another topic of their study is a so-called "runaway" effect in two-dimensional systems, which leads to the negative differential resistance. Their preliminary estimates show that, in contrast to a three dimensional case, such runaway takes place even for deformation optical and acoustic phonon scattering. It should lead to a negative differential mobility in 2D systems based on silicon (germanium). One of the main tasks of the project is to investigate a possibility of the Gunn generation in 2D Si (Ge) MOS structures. The consequences of the negative differential in the two-dimensional FET channel will be studied. This case should differ substantially from the conventional three-dimensional Gunn effect since diffusion non-exponential law governs the charge relaxation in two-dimensional FET channel. The role of electron-electron interactions for 2D "runaway" will also be investigated.