Carrier Localisation in Inversion Layers and Impurity Bands.
Annual technical rept. Sep 78-Nov 79,
CAMBRIDGE UNIV (ENGLAND) CAVENDISH LAB
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Results are presented covering three areas of investigation. The first is the observation and interpretation of spin dependent recombination in silicon gate controlled p-n junctions. The resonance of surface states near mid-gap was detected on MNOS and electron irradiated, 100, devices. The second investigation commenced with the discovery of conductance oscillations in GaAs FET structures below about 10 K. The objective of the experiment was to investigate localisation in conventional GaAs FETs and also structures where the epitaxial n layer was deposited onto a p substrate. In this latter structure the conducting channel was pushed away from the metallurgical interface and the associated disorder. It was found that when the carrier concentration was less than or approximately 10 to the 11th power per sq. cm, the conductance, oscillated as a function of gate voltage. Weaker oscillations have now also been found in conventional FETs. The third, and final, area covered in this report is the observation of strong oscillations in Si MOSFETs in the same temperature range as the GaAs effect. The gate voltage required for a minimum did not shift with substrate bias, indicating that the effect was occuring in the accumulated regions on the source and drain. At present the origin of the oscillations is not clear but we can eliminate the interface as this will not be relevant for GaAs. Author
- Solid State Physics