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Yu. O. Kruglyak
«Physics of Nanotransistors: Ballistic Injection Rate and Combining a Ballistic Model with a Virtual Source Model»
057–079 (2019)

PACS numbers: 71.20.Nr, 72.80.Ey, 73.23.Ad, 85.30.De, 85.30.Tv, 85.35.-p, 85.40.Bh

The review considers the dependence of the electron velocity on the drain voltage in ballistic MOSFETs as well as its dependence on both the gate voltage and on the inversion charge. At first glance, it seems unusual that, in the ballistic MOSFET, the velocity is saturated with the increase in the drain voltage in the absence of electron scattering; however, the physics of this phenomenon is now quite understandable. In ballistic MOSFET, the electron velocity is not saturated at the drain end of the conduction channel, as in massive transistors where the electric field is largest and the scattering is intense, but at the source ends where the conduction channel begins, i.e., at the top of the barrier where the electric field is zero. The saturation of the velocity known as the ballistic injection rate is also discussed. This velocity is the upper limit of the injection rate in real MOSFETs. If , then the ballistic injection rate is constant, however, for , this velocity increases with increasing surface density of electrons. Simple calculations of the ballistic injection rate are made and can be served as a starting point for more thorough calculations. It is shown how the ballistic model and the virtual source model are interrelated. By simple replacing the traditional mobility, which is limited by scattering, in the virtual source model by ballistic mobility, we obtain the correct course of the ballistic linear current. By replacing the saturation velocity in the massive conduction channel by the ballistic injection rate , we obtain the correct value of the ballistic current . As also shown, the ballistic model predicts larger currents than the experimental data. This is due to the effects of electron scattering, understanding of which is extremely important for the modelling of nanotransistors.

Keywords: nanoelectronics, field effect transistor, MOSFET, LDL model, transistor metrics, transistor control, virtual source

https://doi.org/10.15407/nnn.17.01.057