Time-resolved studies of a rolled-up semiconductor microtube laser

Abstract

We report on lasing in rolled-up microtube resonators. Time-resolved studies on these semiconductor lasers containing GaAs quantum wells as optical gain material reveal particularly fast turn-on-times and short pulse emissions above the threshold. We observe a strong red-shift of the laser mode during the pulse emission which is compared to the time evolution of the charge-carrier density calculated by rate equations.The most studied semiconductor microcavity lasers are micropillars 1,2 , microdisks 3,4 and photonic crystals 5,6 . Their small size combined with high quality factors exhibits the possibility of low threshold lasing and single mode operation. Besides the pursuit of lowering the threshold also fast turn-on-times are desirable 4,5 . Presently the fastest turn-on-times were achieved by using quantum wells (QWs) as gain material 5 which have the disadvantage of high non-radiative recombination rates in the vicinity of the structured surfaces. To overcome this problem the surface can be passivated 7,8 . Quantum dots offer a much lower surface recombination rate 9 but have the disadvantage of a low carrier capture rate 10 which lengthens the turn-on-time. In this work we present lasing in microtubes. These structures have the intrinsical advantage of nearly no unpassivated surfaces. Exploiting the self-rolling mechanism of thin strained semiconductor bilayers 11 we fabricated multiwalled microtubes that act as optical ring resonators 12 . As optical gain medium we chose a GaAs QW. Applying sub-picosecond optical pumping we measured the time evolution of the photoluminescence (PL) emission at low temperature.Our samples were grown by molecular beam epitaxy on 001 GaAs substrates. On top of a 40 nm AlAs sacrificial layer a 42 nm thick layer system is grown consisting of a 16 nm thick pseudomorphically strained barrier layer of In 0.16 Al 0.30 Ga 0.54 As, a 4 nm GaAs QW, and a 22 nm Al 0.20 Ga 0.80 As barrier. By selectively etching the sacrificial layer a predefined U-shaped mesa rolls up and forms a free-standing microtube bridge. Details of the fabrication are described in Refs. 12,13. The tube investigated in this work is shown in Fig. 1(a). It has a diameter of 5.74 µm and 1.1 revolutions. In the free-standing part total internal reflection leads to waveguiding in the tube wall and to the formation of ring modes by constructive interference after a roundtrip 12 . Very recently we showed † present address:

Strong Coupling in a Photonic Molecule Formed by Trapping a Microsphere in a Microtube Cavity

“…[35] To combine with other media/objects, luminescent quantum dots, [36,37] quantum wells, [38] and organic molecules [39] have been enwrapped into the microtube wall by the rolling up process, which couple photoluminescence (PL) light to the microtube cavities to support whisperinggallery mode (WGM) resonances. [37,40] In this context, a design and demonstration of photonic molecule based on microtube cavity is of fundamental interest for the study of strong optical coupling and the promo tion of its potential applications.…”

“…[37,40] In this context, a design and demonstration of photonic molecule based on microtube cavity is of fundamental interest for the study of strong optical coupling and the promo tion of its potential applications.…”

Dynamic Molecular Processes Detected by Microtubular Opto‐chemical Sensors Self‐Assembled from Prestrained Nanomembranes

“…For example, functional units based on rolled‐up nanomembranes include optical ring resonators,3, 4 ultra‐compact energy storage devices,5, 6 magnetic sensors,7 spin‐wave resonators,8 novel concepts for metamaterials9, 10 and superconducting devices11 as well as autonomous microengines12, 13 and full lab‐in‐a‐tube systems 14, 15. The possibility to shape nanomembranes out of many different materials and material combinations into vertical optical ring resonators3, 4 is particular exciting and has led to the fabrication of microtube lasers16, 17 and optofluidic components,18–20 which are extremely sensitive to refractive index changes caused by different fluids inserted into the hollow core of the microtube 19, 20. Because the light is guided by and within the sub‐wavelength thin walls of the rolled‐up microtube, the evanescent part of the confined whispering gallery modes (WGM) is expected to be particularly sensitive to tiny alterations and modifications in the vicinity of the inner and outer tube wall surfaces.…”

Cyclization of Synthetic seco‐Proansamitocins to Ansamitocin Macrolactams by Actinosynnema pretiosum as Biocatalyst

“…The confinement of both carriers and photons may lead to lower lasing thresholds 255. Experimental results concerning rolled‐up microtube lasers were reported recently, and a low threshold of ∼4 μW has been achieved 257, 263. Moreover, due to a tube wall that is generally thinner than the light wavelength, the light energy cannot be completely confined within the resonator wall.…”