Negative differential conductivity in shallow-impurity hopping
Charge carriers in shallow-impurity states in semiconductors are weakly coupled to the phonons. As such, hopping impurity conduction proceeds via a succession of jumps in which a single phonon is either emitted or absorbed. Hops can only occur between states which differ in energy by less than the energy of the maximum energy phonon which can be emitted or absorbed. With the application of a large electric field, hops nearly parallel to the direction of the applied electric field are precluded since their attendant energy difference is too great. As a result, at high electric fields energetically allowed hops are nearly perpendicular to the applied field. This results in a drift velocity which falls with electric field strength at large electric fields. The criterion for being in this ''high-field'' regime is that the electric-field-induced drop in potential energy between a typical pair of sites be greater than the energy of the highest-energy phonon with which the carrier interacts appreciably. For a large-radius impurity state the maximum energy acoustic phonon with which the impurity state interacts is a very small fraction of the Debye energy. With a large-radius impurity concentration of 10/sup 15/ cm/sup -3/ in highly compensated Ge, high-field behavior is expected to occur for internal electric fields above 2.4 x 10/sup 2/ V/cm.
- Research Organization:
- Sandia National Laboratories, Albuquerque, New Mexico 87185
- OSTI ID:
- 6333920
- Journal Information:
- Phys. Rev. B: Condens. Matter; (United States), Journal Name: Phys. Rev. B: Condens. Matter; (United States) Vol. 32:10; ISSN PRBMD
- Country of Publication:
- United States
- Language:
- English
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