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(Color online) (a) MBE sequence for the fabrication of rolled-up tubes containing InAs QDs as quantum emitters in the tube walls; (b) schematic of a tube rolled up from a lithographically defined strained stripe; (c) corresponding light microscope image. The strained stripe (pink) is rolled up into tubes on both sides. The number of rotations (2.5), length , and location of the tubes can be tuned by lithographic means. The diameter depends on the strained layer thickness and composition.
(Color online) spectra from the flat unetched area (blue curve) and the rolled-up tube area (red curve). The light is collected directly from the laser excitation spot for both spectra. The curves are offset for clarity. In the inset, the strain-induced change in band structure and quantized energy levels is illustrated. The colors correspond to the spectra. The zero of the position axis in the inset corresponds to the top surface in Fig. 1(a).
(a)–(c) PL images (upper row) for three illumination conditions together with schematics (lower row). The laser excitation moves from the unetched area (a), to the tube (b), and finally to the etched area (c). The arrows in (b) point at waveguided light at the tube exits. (d) spectra with laser excitation at the center of the tube as shown in (b). As illustrated by the inset, the dotted curve shows the signal collected at the laser excitation point and the solid curve shows the signal collected at the tube exits.
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