A slow positron beam has been utilized for investigating vacancy defects in semiconductor nanostructures. The studied structures were GaIn(N)As/GaAs superlattices for telecommunication applications [1] and AlSb/GaSb superlattices for optoelectronic applications [2]. The complete superlattice structures consisted of ten periods of quantum wells separated by barriers. The total thickness of the structures was 150-300 nm, with a quantum well thickness of 6-13 nm and a barrier thickness of 2–30 nm. A capping layer was deposited on both structures in order to improve the sensitivity of used defect probing technique, positron annihilation spectroscopy (PAS).
The results show that PAS can be used to study such thin layers. Differences in vacancy defect between annealed and as grown structures are observed for both superlattice structures. For the GaIn(N)As/GaAs structures it is observed that nitrogen incorporation into the quantum wells and subsequent heat treatment induces optically inactive vacancy-type defects in the superlattice structures. For the AlSb/GaSb superlattices the annealing behavior of the samples differs depending on the used substrate. A reduction in vacancy defects with annealing time is observed for samples grown on undoped GaSb, where as an increase in vacancy defects is observed for samples grown on Te doped GaSb.
[1] J. Slotte, K. Saarinen, E.-M. Pavelescu, T. Hakkarainen and M. Pessa, Appl. Phys. Lett. 89, 061903 (2006).
[2] J. Slotte, M. Gonzalez-Debs, T. F. Kuech and J. G. Cederberg, submitted to Journal of Applied Physics.
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