Phonons in GaAs/AlAs superlattices grown along the

GaAs/GaP superlattice nanowires: growth, vibrational and optical properties

Nanowire geometry allows semiconductor heterostructures to be obtained that are not achievable in planar systems, as in, for example, axial superlattices made of large lattice mismatched materials. This provides a great opportunity to explore new optical transitions and vibrational properties resulting from the superstructure. Moreover, superlattice nanowires are expected to show improved thermoelectric properties, owing to the dominant role of surfaces and interfaces that can scatter phonons more effectively, reducing the lattice thermal conductivity. Here, we show the growth of long (up to 100 repetitions) GaAs/GaP superlattice nanowires with different periodicities, uniform layer thicknesses, and sharp interfaces, realized by means of Au-assisted chemical beam epitaxy. By optimizing the growth conditions, we obtained great control of the nanowire diameter, growth rate, and superlattice periodicity, offering a valuable degree of freedom for engineering photonic and phononic properties at the nanoscale. As a proof of concept, we analyzed a single type of superlattice nanowire with a well-defined periodicity and we observed room temperature optical emission and new phonon modes. Our results prove that high-quality GaAs/GaP superlattice nanowires have great potential for phononic and optoelectronic studies and applications.

Lattice dynamics and Raman scattering by phonons of GaAs/AlAs(001) superlattices

The lattice dynamics of (GaAs)(n)/(AlAs)(n)(001) superlattices (SLs), n = 1,2, with perfect and disordered (non-perfect) interfaces is studied in detail. The SLs with disordered interfaces are approached by primitive cells, much larger in volume than that of the perfect SL primitive cell. The dynamical matrices of the SLs have been constructed from a combination of the dynamical matrices corresponding to the bulk crystalline constituents, while the interionic forces are calculated by using a ten-parameter valence overlap shell model (VOSM). Furthermore, we calculate the Raman spectra, for both perfect and disordered superlattices by using an eight-parameter bond polarizability model (BPM). Our theoretical results are in very good agreement with the available experimental spectra. Finally, our results clearly demonstrate that intermixing of Ga and Al cations, even to a very small extent, can induce Raman activity, which although not expected in the spectra of perfect superlattices, is actually observed experimentally.