Polarized emission from GaN/AlN quantum dots: Single-dot spectroscopy and symmetry-based theory

Abstract

We report micro-photoluminescence studies of single GaN/AlN quantum dots grown along the (0001) crystal axis by molecular beam epitaxy on Si(111) substrates. The emission lines exhibit a linear polarization along the growth plane, but with varying magnitudes of the polarization degree and with principal polarization axes that do not necessarily correspond to crystallographic directions. Moreover, we could not observe any splitting of polarized emission lines, at least within the spectral resolution of our setup (1 meV). We propose a model based on the joint effects of electron-hole exchange interaction and in-plane anisotropy of strain and/or quantum dot shape, in order to explain the quantitative differences between our observations and those previously reported on, e.g. CdTe-or InAs-based quantum dots.

Direct generation of linearly polarized single photons with a deterministic axis in quantum dots

“…Results on both InGaAs QDs [30] and c-plane InGaN QDs [15,16] reveal that dot shape anisotropy plays an important role and affects their properties quite significantly due to band mixing effects. Anisotropy affects the degree of quantum confinement, which causes energetic shifts in the | -, X〉 | -Y 〉 and | -Z〉 like state and, thus, their contribution to the band mixing effects for the hole ground state.…”

“…These polarized single-photon sources can then fulfill the need for on-chip polarization encoding in quantum cryptography, such as the BB84 protocol [20]. However, previous studies of polar c-plane (0001) InGaN QDs reveal that only selected QDs with large-shape anisotropies can exhibit high degrees of optical linear polarization (DOLP) [15,16], which are also in agreement with our own investigations [21]. Furthermore, in most conventional c-plane nitride QD systems, different anisotropies could result in random polarization axes, which are highly undesirable in the implementation of polarization-based protocols in potential applications.…”

“…In this work, we report a combined theoretical and experimental investigation of a planar epitaxial selfassembled semiconductor QD system -non-polar a-plane (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) InGaN/GaN QDs -that provides not only a statistically high DOLP but also a fixed polarization direction determined by the underlying material crystallography. Furthermore, while the DOLPs of a-plane quantum wells (QWs) are limited to ~0.60 [26], we report a much higher average DOLP of ~0.90 in a-plane InGaN QDs.…”

“…To develop these non-classical light sources, the nanophotonics of semiconductor quantum dots (QDs) [7][8][9] has been a field under intense scientific investigation. Although ultrapure and highly indistinguishable single-photon generation has been achieved in various arsenide-based QD systems [10][11][12][13][14], the large band offsets and strong exciton binding energies of III-nitride materials are needed for the realization of polarized photon emission [15][16][17] and room temperature operation [18,19]. These polarized single-photon sources can then fulfill the need for on-chip polarization encoding in quantum cryptography, such as the BB84 protocol [20].…”

Direct generation of linearly polarized photon emission with designated orientations from site-controlled InGaN quantum dots

“…The polarization direction of the ground-state-related emission from the QDs reflects the axis of in-plane anisotropy of the confining potential, concerning both strain and/or QD shape. 22,23 The same polarization direction for different QDs indicates that all grown QDs possess the same unidirectional in-plane anisotropy. Such simultaneous alignment of multiple QDs with controllable orientations has not been reported up to now to the best of our knowledge.…”