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.

Single GaN/Al(Ga)N quantum dots (QDs) have been investigated by means of microphotoluminescence. Emission spectra related to excitons and biexcitons have been identified by excitation power dependence and polarization resolved spectroscopy. All investigated dots exhibit a strong degree of linear polarization (∼90%). The biexciton binding energy scales with the dot size. However, both positive and negative binding energies are found for the studied QDs. These results imply that careful size control of III-Nitride QDs would enable the emission of correlated photons with identical frequencies from the cascade recombination of the biexciton, with potential applications in the area of quantum information processing.

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