Growth and spectroscopic ellipsometry evaluation of composite layers of ErAs and InAs nanoparticles

Metal nanoparticles coupled to semiconductor quantum dots have been studied recently due to the enhancement in absorption, emission, and nonlinearities expected from these hybrid structures. These properties stem from the ability of the metal to focus light as well as shift the phase, which occurs at the metal-dielectric interface. To date, most quantum dots metal nanoparticle couples are formed by the attachment of a ligand to both particles. The extension of this idea to bulk semiconductor films is being attempted by the formation of a composite structure of ErAs, which forms semimetallic nanoparticles (SMNP) in GaAs, and InAs self-assembled quantum dots (SAQD). In this work, the authors analyze structures composed of periods of InAs SAQDs and ErAs SMNPs and analyze these with spectroscopic ellipsometry in the spectral region 0.7-4.0 eV with 0.02 eV steps. Initially, individual structures composed of InAs SAQD stacks or ErAs SMNP stacks, both capped with layers of GaAs, are analyzed. The authors have also analyzed the films with high-resolution x-ray diffraction. The structural parameters from x-ray models are used in conjunction with the spectroscopic ellipsometry data to extract the homogenized refractive index for the individual stacks. The properties of these films are then used to calculate the properties of a composite structure composed of eight repeats of periods, which contain a growth sequence used to form the stacks of InAs SAQDs and ErAs SMNPs. The authors find that this composite structure is best modeled with a Bruggeman effective medium mixture of the two component stacks and a thin intermediate layer of constant index of refraction to account for the reflections at the boundaries between the periods.