Polarized light from excitonic recombination in selectively etched GaN/AlN quantum dot ensembles on Si(111)

Abstract

Multiple layers of GaN/AlN quantum dot (QD) ensembles were grown by the Stranski–Krastanov method on Si(111) using molecular beam epitaxy. During the subsequent cooling from growth temperature, the thermal expansion coefficient mismatch between the Si substrate and GaN/AlN film containing the vertically stacked QDs leads to an additional biaxial tensile stress of 20–30 kbar in the III-nitride film. We have selectively modified the thermal stress in the QD layers by etching a cross-hatched pattern into the as-grown sample using inductively coupled Cl2/Ar plasma reactive ion etching. The results show that a suitable choice of stripe width from ∼2 to 10 µm and orientation along [11−20] and [1−100] can create regions of in-plane uniaxial stress that enable a selective and local control of the polarized luminescence from ensembles of QDs which were probed with cathodoluminescence. Experimental results indicate that the polarization anisotropy vanishes at high temperatures (∼300 K) with an increasing e–h pair excitation for the QDs, while the anisotropy decreases more slowly with excitation at low temperatures (∼46 K). A theoretical modelling of the effect of carrier filling on the polarization anisotropy and the excitonic transition energy was performed, as based on three-dimensional self-consistent solutions of the Schrödinger and Poisson equations using the and effective-mass methods for calculations of the e–h wavefunctions and electron and hole quasi-Fermi levels for varying levels of state filling. We attribute carrier filling and a thermal excitation of holes into higher energy QD hole states during e–h pair excitation to account for the observed gradual decrease in the polarization anisotropy with an increasing e–h pair excitation density at T = 300 K.