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

Abstract

Semiconductor quantum dots (QDs) have been demonstrated viable for efficient light emission applications, in particular for the emission of single photons on demand. However, the preparation of QDs emitting photons with predefined and deterministic polarization vectors has proven arduous. Access to linearly polarized photons is essential for various applications. In this report, a novel concept to directly generate linearly-polarized photons is presented. This concept is based on InGaN QDs grown on top of elongated GaN hexagonal pyramids, by which the predefined elongation determines the polarization vectors of the emitted photons from the QDs. This growth scheme should allow fabrication of ultracompact arrays of photon emitters, with a controlled polarization direction for each individual emitter. Keywords: GaN; InGaN; photoluminescence; polarized emission; quantum dot INTRODUCTION Quantum dots (QDs) have validated their important role in current optoelectronic devices and they are also seen promising as light sources for quantum information applications. An improved efficiency of laser diodes and light-emitting diodes can be achieved by the incorporation of QDs ensembles in the optically active layers.1 In addition, the proposed quantum computer applications rely on photons with distinct energy and polarization vectors, which can be seen as the ultimate demand on photons emitted from individual QDs.2 A common requirement raised for several optoelectronic applications, e.g., liquid-crystal displays, three-dimensional visualization, (bio)-dermatology 3 and the optical quantum computers, 4 is the need of linearly polarized light for their operation. For existing applications, the generation of linearly polarized light is obtained by passing unpolarized light through a combination of polarization selective filters and waveguides, with an inevitable efficiency loss as the result. These losses can be drastically reduced by employment of sources, which directly generate photons with desired polarization directions.Conventional QDs grown via the Stranski-Krastanov (SK) growth mode are typically randomly distributed over planar substrates and possess different degrees of anisotropies. The anisotropy in strain field and/or geometrical shape of each individual QD determines the polarization performance of the QD emission. Accordingly, a cumbersome post-selection of QDs with desired polarization properties among the randomly distributed QDs is required for device integration.

Polarized single photon emission and photon bunching from an InGaN quantum dot on a GaN micropyramid

“…Under optimized growth conditions, most pyramids accommodate only one QD each [8] but this particular pyramid reveals spectral features of more than one QD. A small pyramid-to-pyramid variation of the top surface may be the reason for this, as truncated pyramids with intentionally larger top surface are known to accommodate more QDs [9].…”

“…QDs formed on the apex of the pyramids grown with this approach have been shown to exhibit single and sharp InGaN related emission lines with a high degree of linear polarization. A simple elongation of the pyramid base gives control of the polarization direction [8,9]. The photon statistics of these pyramidal QDs have recently been shown to exhibit anti-bunching, but an spectrally overlapping background emission of uncorrelated photons will vanish high-performance single photon characteristics of the * tomje@ifm.liu.se emission [10].…”

“…The photon statistics of these pyramidal QDs have recently been shown to exhibit anti-bunching, but an spectrally overlapping background emission of uncorrelated photons will vanish high-performance single photon characteristics of the * tomje@ifm.liu.se emission [10]. Cathodoluminescence measurements have revealed that the broad background emission mainly originates from the bottom edges near the pyramid base [9].…”

Linearly polarized single photon antibunching from a site-controlled InGaN quantum dot

“…14 Moreover, a simple elongation of the pyramid base gives control of the polarization direction of the InGaN emission, as it is found to be well-aligned with the designed elongation. 15 The first experimental evidence of a trion in a nitride QD has also been reported for these structures. 16 However, although several indirect evidences of QD formation in these pyramidal structures have been observed, no direct proof has yet been provided.…”

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

“…Consequently, much effort is needed to define the anisotropy, in order to obtain consistently high DOLPs with deterministic polarization directions. Such experimental reports in the nitrides are limited to the manipulation of pyramidal geometries [22], elliptical QDs [23], or the use of nanowires [24,25], where the geometries of the structures make electrical contacting challenging. As such, a simpler and more practical method is needed to achieve polarization control, for the realization of on-chip polarized single-photon generation and related applications.…”