Single Excitons in InGaN Quantum Dots on GaN Pyramid Arrays

Abstract

Fabrication of single InGaN quantum dots (QDs) on top of GaN micropyramids is reported. The formation of single QDs is evidenced by showing single sub-millielectronvolt emission lines in microphotoluminescence (μPL) spectra. Tunable QD emission energy by varying the growth temperature of the InGaN layers is also demonstrated. From μPL, it is evident that the QDs are located in the apexes of the pyramids. The fact that the emission lines of the QDs are linear polarized in a preferred direction implies that the apexes induce unidirected anisotropic fields to the QDs. The single emission lines remain unchanged with increasing the excitation power and/or crystal temperature. An in-plane elongated QD forming a shallow potential with an equal number of trapped electrons and holes is proposed to explain the absence of other exciton complexes.

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

“…There is also a weak low energy shoulder on XX but characterized by a polarization direction different from that of X and XX and, therefore, concluded to originate from another QD. 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].…”

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

“…Selective area regrowth of GaN pyramids is performed in the lithographically patterned SiN masked GaN/AlN/SiC template. 14 (See the inset in Fig. 1) The pyramids are covered by a thin layer of InGaN forming nanoscopic 3D islands in a SK-like growth mode on the truncated (0001) top surface.…”

The charged exciton in an InGaN quantum dot on a GaN pyramid

“…4,[7][8][9] By employing such spatially isolated QDs, the typical large inhomogeneous broadening, as well as dot-todot interactions, can be avoided. 10 This facilitates the spectral identification, 11 and a detailed polarized fine structure has been revealed in III-As QDs.…”

“…The presence of merely a single exciton can be ascribed to a shallow confinement potential in which solely the single neutral exciton state is bound. 9 Other excitonic complexes in III-nitride QDs, like the charged exciton and biexciton, are expected to appear at higher energies than the single exciton due to the strong repulsive Coulomb interactions, thus being unbound for the case of shallow barriers. 13 In QD2, only one emission line, denoted as X A , is recorded at low P ex and/or T. However, an additional emission line, denoted as X B , appears with increasing P ex and/or T ( measurements, X A and X B , are linearly polarized in the same direction and with a similar degree of polarization, 14 which can be interpreted as two different exciton complexes originating from the same QD involving the same hole state.…”