Current Instability and Gunn Effect in Two-Dimensional Systems

Rensselaer Polytechnic Institute, Troy NY

Investigators

Abstract

0080509 Shur The 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.