An AFM combined with a SEM has been used to
study the topography and the local electronic transport through InAs QDs grown
by metalorganic vapour phase epitaxy (MOVPE) on an n-type InP(0 0 1) substrate
and covered by a 5 nm thick InP cap-layer. Images reveal that elliptic
terrace-like structures have been formed around the QDs and that the height of
the QDs has been decreased to that of the cap-layer. The electric current is
very high on the dots, about ten times less on the terraces, and not detectable
on the wetting layer. Mechanisms of electronic transport through the sample are
discussed, based on current–voltage characteristics and energy band diagrams.
The detection of the electron beam induced current (EBIC) with the conductive
probe shows that the minority carrier diffusion length, the holes in our case,
is about two times larger than that of the reference sample containing no QDs.
Mechanisms of charge trapping inside the QDs and the surrounding terraces in
forward bias conditions are also discussed. A temporary memory effect is
evidenced.
Source:IOPscience
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