2. Electron Scattering Length - Mean Free Path – le - Avg. distance between scattering Si - ~ 5nm; GaAs - ~ 100 nm Electrical Resistance is closely related to le Macroscopic Devices

3. Mesoscopic Devices Active device length is smaller than the Scattering Length Electrons may travel without encountering scattering from the randomly distributed scatterers Electrons are scattered only at the device boundaries Newtonian billiard-ball model

4. Electrons free to move in two dimensions but tightly confined in the third In some heterostructure semiconductors with offset conduction bands Triangular “well” formed at the interface goes slightly below the Fermi energy so that electrons can collect there Reduces impurity scattering - increasing the electron mobility

5. No random scattering - very high intrinsic working speed and a quick response No temperature dependent phonon scatterings - temperature independent Electron transport can be, to a large extent, modified and controlled by designing the device boundaries Ballistic Devices Ballistic Rectifier Mesoscopic Ballistic Detectors Ballistic Y - Branch Switch Conventional Ballistic Transistors Ballistic Deflection Transistor

6. The asymmetric triangular structure, deflects the electrons downward – rectification AC or RF source is connected across the left and right contacts DC voltage is developed across the top and the bottom contacts

7. Mesoscopic solid-state structures as both quantum systems and as detectors Operation: The ability of a measured system to control the transport of some particles between the two reservoirs Most direct form - Quantum Point Contact Output is the electric current I due to ballistic electrons driven by the voltage difference V between the electrodes Current depends on the electron transmission probability – state of the system

8. “Y” configuration with one source and two drain terminals Electric field steers the injected electron wave into either of the two output drain arms Electrons need not be stopped by a barrier - fast switching times and low power consumption The 2DEG channel increases the mean free path of the electrons, making YBS to operate in the terahertz ballistic regime Used as ballistic logic gates with possibility of cascading

9. Heterojunction Bipolar Transistor (HBT) The main difference between the BJT and HBT - Different semiconductor material for emitter and base regions, creating heterojunction High doped base, forming 2DEG layer - higher electron mobility while maintaining gain Applications: Optoelectronic integrated circuits and mixed signal circuits such as analog-to-digital and digital-to- analog converters Heterojunction Bipolar Transistor (HBT) High Electron Mobility Transistor (HEMT)

10. Field effect transistor with the 2DEG in heterojunction layer as channel Hence channel has low resistance or high electron mobility Applications: Microwave and millimeter wave communications, radar and radio astronomy

11. Ballistic transport in the 2DEG layer provides the actual transistor nonlinearity Vdd accelerates electrons from Vss towards the central junction of the BDT A small gate voltage modifies the path of the electrons towards the right or the left These electrons are then ballistically deflected from the central triangular feature into one or the other output channels

13. Review of a novel and unique concept of electronic devices capable of working at high frequencies Devices with ballistic transport Low power consumption and produces low noise levels Multitude of applications like high speed processors, RF identification, wireless fidelity

14. [1] A. M. Song, “Room-Temperature Ballistic Nanodevices”, Encyclopedia of nanoscience and Nanotechnology, X, 1 (2004) [2] S. Datta, Electronic Transport in Mesoscopic Systems (Cambridge University Press, Cambridge, 1995) [3] D. V. Averin, “Mesoscopic Quantum Measurements”, available online at http://arxiv.org/abs/cond-mat/0603802http://arxiv.org/abs/cond-mat/0603802 [4] E. Forsberg: "Reversible logic based on electron waveguide Y-branch switches", Nanotechnology 15, S298 (2004) [5] Wikipedia contributors at http://www.en.wikipedia.orghttp://www.en.wikipedia.org [6] Q. Diduck, M. Margala, and M. J. Feldman, “A Terahertz Transistor Based on Geometrical Deflection of Ballistic Current”, IEEE Microwave Symposium Digest, 345 (2006)