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We have investigated the influence of Si–N complexes on the electronic properties of GaAsN alloys. The presence of Si–N complexes is suggested by a decrease in carrier concentration, n, with increasing N-composition, observed in GaAsN:Si films but not in modulation-doped heterostructures. In addition, for GaAsN:Te (GaAsN:Si), n increases substantially (minimally) with annealing-T, suggesting a competition between annealing-induced Si–N complex formation and a reduced concentration of N-related traps. Since Si–N complex formation is enhanced for GaAsN:Si growth with the (2×4) reconstruction, which has limited group V sites for As–N exchange, the (Si–N)As interstitial pair is identified as the dominant Si–N complex. [ABSTRACT FROM AUTHOR]

The authors introduce an all-optical approach to study the propagation of high frequency acoustic phonons in which the generation and detection involves two spatially separated superlattices ∼1 μm apart. Propagating modes of frequencies up to ∼1 THz escape from the superlattice where they are generated and reach the second superlattice where they are detected and spectrally resolved using pump-probe techniques. The measured frequency spectrum reveals finite size effects, which can be accounted for by a continuum elastic model. [ABSTRACT FROM AUTHOR]