Wave propagation in negative resistance media

• Main Author: Baynham, Alexander Christopher
• Published: University of Warwick 1971
• Subjects: 530; QC Physics
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.594957

When an e1eotromagnetio wave enters a medium having an effective negative resistance, it may be expected to grow spatially. The conditions under which such growth may be observed are examined, and an experimental regime chosen where it should be possible to observe these effects. Suchh observations can throw light not only upon the negative resistance travelling wave amplification process, but also upon the transport process giving rise to the host negative resistance. The experimental work is therefore divided between a study of a new negative differential conductivity process recently discovered in n-Ge and a study of the negative résistancee travelling wave amplification process in GaAs. The diagnostic measurements upon n-Ge provide new data relating to the negative resistance process in that material; data such as the maximum negative slope mobility of 300 cm 2 /V.sec. at 77°K (E / / <100» the threshold electric field for N.D.C. of 2.95KV/cm. (E //<100»), and the ceiling frequency of 5 GHz beyond which N.D.C. disappears, all of which have been subsequently corroborated by other workers. Observations of the emission spectrum from GaAs, when the amplified electromagnetic wave begins to experience round trip gain within the specimen cavity, have allowed some fairly detailed discussion to be undertaken concerning the nature of the emission process, which rely upon careful measurements of the spectral power and line width. Although the maximum pulse power observed of 4mW is low, such observations of emission do provide anew mechanism by which microwave power may be extracted from a suitably biased material having a negative differential conductivity. Finally, attention is directed towards some potentially profitable areas for future work.