Abstract Prof. Davies
|Prof. John Davies, University of Glasgow|
"The effects of strain from metal gates on a heterostructure"
It is now well established that metal gates deposited on a heterostructure
produce an elastic field as well as the intended electrostatic field. The
elastic field couples to electrons through two mechanisms, the deformation
potential which is isotropic and the piezoelectric coupling which depends
strongly on orientation. Recent experiments on lateral surface
superlattices confirm that the piezoelectric coupling generally dominates.
We have calculated analytically the strain, piezoelectric charge density,
and potential induced in the two-dimensional electron gas by single gates
and one-dimensional surface superlattices. Typically the piezoelectric
potential is equivalent to about 0.1 V on the gates. Different behaviour is
seen on (001), (011) and (111) surfaces.
Larger strains may be introduced during the manufacture of III-V
field-effect transistors, particularly due to nitride passivating layers.
These can lead to changes in threshold voltage of 0.5 V. Interesting
problems are also posed by the highly stressed nature of pseudomorphic