Letter Cite This: Nano Lett. 2018, 18, 6292−6300
pubs.acs.org/NanoLett
Tuning Lasing Emission toward Long Wavelengths in GaAs(In,Al)GaAs Core−Multishell Nanowires T. Stettner,*,† A. Thurn,† M. Döblinger,‡ M. O. Hill,§ J. Bissinger,† P. Schmiedeke,† S. Matich,† T. Kostenbader,† D. Ruhstorfer,† H. Riedl,† M. Kaniber,† L. J. Lauhon,§ J. J. Finley,† and G. Koblmüller*,† †
Walter Schottky Institut and Physik Department, Technische Universität München, 85748 Garching, Germany Department of Chemistry, Ludwig-Maximilians-Universität München, 81377 München, Germany § Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, United States Nano Lett. 2018.18:6292-6300. Downloaded from pubs.acs.org by IOWA STATE UNIV on 01/17/19. For personal use only.
‡
S Supporting Information *
ABSTRACT: Semiconductor nanowire (NW) lasers are attractive as integrated on-chip coherent light sources with strong potential for applications in optical communication and sensing. Realizing lasers from individual bulk-type NWs with emission tunable from the near-infrared to the telecommunications spectral region is, however, challenging and requires low-dimensional active gain regions with an adjustable band gap and quantum confinement. Here, we demonstrate lasing from GaAs-(InGaAs/AlGaAs) core−shell NWs with multiple InGaAs quantum wells (QW) and lasing wavelengths tunable from ∼0.8 to ∼1.1 μm. Our investigation emphasizes particularly the critical interplay between QW design, growth kinetics, and the control of InGaAs composition in the active region needed for effective tuning of the lasing wavelength. A low shell growth temperature and GaAs interlayers at the QW/ barrier interfaces enable In molar fractions up to ∼25% without plastic strain relaxation or alloy intermixing in the QWs. Correlated scanning transmission electron microscopy, atom probe tomography, and confocal PL spectroscopy analyses illustrate the high sensitivity of the optically pumped lasing characteristics on microscopic properties, providing useful guidelines for other III−V-based NW laser systems. KEYWORDS: Nanowire lasers, quantum wells, monolithic III/V integration on Si, InGaAs, scanning transmission electron microscopy, photoluminescence, molecular beam epitaxy
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telecommunications band with a tunable emission wavelength has not been demonstrated for isolated NWs and a 3D (bulk) gain medium. Although band gap tunable bulk III−V NWs, e.g., InGaAs nanopillars, can be monolithically integrated on silicon and silicon-on-insulator platform,19 lasing at telecom wavelengths was only achieved in one-dimensional photonic crystal arrays.6 An alternative approach for tuning lasing wavelength to the desired spectral range is to use quantum-confined structures such as quantum wells (QW) or quantum dots (QD) as the active gain medium. Due to their modified density of states20 these low-dimensional gain media are expected to simultaneously improve lasing performance by lowering the lasing threshold while increasing modulation bandwidth, differential gain, and temperature stability.2,4,21 Furthermore, coaxial QWs in core−shell NW lasers can host optical modes that may
emiconductor nanowires (NWs) offer new routes toward coherent nanoscale light sources that can be monolithically grown on low-cost Si substrates1−4 and be site-selectively integrated onto silicon photonic circuits.3,5−7 Their unique geometry allows a wide range of different materials to be grown site selectively on Si, despite the presence of considerable lattice mismatch. Moreover, they facilitate low-loss singlemode optical waveguiding, integrate an internal gain medium and host resonant optical recirculation needed for lasing. Intense research into different NW laser material systems has been ongoing for several years now, with early efforts focused mostly on group-III nitrides8−10 and II−VI materials (e.g., ZnO11,12 and CdS13,14) emitting in the ultraviolet and visible spectral range. More recent endeavors were increasingly directed toward NW lasers in the near-infrared (NIR) using III−V compound semiconductors such as GaAs, InP, and GaAsSb.15−18 Compositional tuning of the bandgap of NW lasers allows their emission wavelength to be tuned toward the technologically relevant telecommunication band (∼1.15−1.5 μm). However, to date, lasing from bulk NW materials in the © 2018 American Chemical Society
Received: June 20, 2018 Revised: August 30, 2018 Published: September 5, 2018 6292
DOI: 10.1021/acs.nanolett.8b02503 Nano Lett. 2018, 18, 6292−6300
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Nano Letters
Figure 1. (a) SEM image of as-grown MQW-NW laser structure on Si (111) with a nominal In molar fraction of 30% grown at a shell temperature of 510 °C. The length is typically ∼6−8 μm and the diameter ∼440 nm, respectively. (b) Cross-sectional STEM-HAADF image overlaid with a schematic illustration of the core−shell MQW heterostructure. (c) High-resolution STEM image of a region close to one of the six {112̅} corners, showing the high-quality interfaces between InGaAs QWs and AlGaAs/GaAs barriers (dashed lines indicate the interfaces).
nanoscale openings in ultrathin SiO2 mask layers, which act as sites of selective nucleation.27 To define the resonator length of the NW laser, the GaAs NW core was grown vertically aligned along the [111] orientation using a self-catalyzed vapor−liquid−solid (VLS) growth at a substrate temperature of 650 °C and Ga and As fluxes of 0.05 and 0.24 nm s−1, respectively. A total growth time of 60 min resulted in ∼6−10 μm long and ∼50−60 nm thick GaAs NWs, similar to our previous experiments.16,22,28,29 After the core was defined, the growth temperature was reduced and As supply increased, in order to consume the Ga droplet and to set conditions for subsequent radial growth at the six {11̅0} NW sidewall facets.16,30 This radial growth step defines the exact cavity width (NW laser diameter) as well as the coaxial InGaAs/ AlGaAs MQW structure. First, an Al0.3Ga0.7As spacer layer was grown at a thickness chosen to maximize the overlap of the gain region with the supported mode (TE01 mode) for the respective emission wavelength. With increasing wavelength emission the entire NW laser cavity needs to be thicker, meaning that the AlGaAs spacer layer thickness was increased accordingly (see FDTD simulations in Supporting Information for more details). After the AlGaAs spacer layer, a total of seven 8 nm thick InxGa1−xAs QWs were embedded, which are separated by 6 nm Al0.3Ga0.7As barriers. Here, an additional 2 nm thin GaAs interlayer was introduced at both upper and lower interfaces of the InGaAs QWs in order to reduce alloy intermixing of the ternary InGaAs and AlGaAs compounds. Corresponding NW lasers were also grown without GaAs interlayers and compared in terms of alloy intermixing (see Supporting Information). The QW and barrier thicknesses were adapted from former studies of GaAs/AlGaAs MQW NW systems22,24 as well as planar structures31,32 to achieve uniform carrier distributions via weakly coupled QWs to achieve low threshold lasing. In total, two distinct series of samples were grown to study the effect of varying In/Ga-flux ratio and temperature on the incorporation of In into the QW region. In the first series, the shell growth temperature was fixed at 510 °C while the nominal In molar fraction was steadily increased up to 40% under a constant group III flux of 0.09 nm s−1 (more details can be found in the Supporting Information). In the second series, the impact of the shell growth temperature in the range 420−510 °C was studied on the In incorporation while the nominal In
provide efficient in-coupling of lasing emission into proximal Si waveguides.7,22,23 In this respect, relatively few near-IR NW lasers using quantum confined gain media have been reported for III−V systems: axial InGaAs QDs in GaAs-based NWs,21 GaAs QWs in GaAs-AlGaAs core−shell NWs,22,24 InGaAs QWs in InP nanopillars (NP),25 and GaAs-GaAsSb QDsuperlattice NW structures.18 In particular, InGaAs QWs arranged in coaxial NP or NW geometries appear most promising as they offer excellent luminescence yield at lasing wavelengths in the Si-transparent wavelength range.25,26 While coaxial InGaAs QW-nanopillar lasers can be realized in the closely lattice-matched InP system, it remains unclear whether they can be also implemented on the well-established GaAs/Si platform where mismatch strain comes into play. Furthermore, the links between lasing characteristics and underlying structural and compositional properties of the respective QWs mediated by QW design and growth kinetics is another open question that remains to be explored. In this work, we demonstrate the growth and explore the lasing properties of monolithically integrated GaAs-(InGaAs/ AlGaAs) core−shell NWs on Si with multiple compositiontunable InGaAs quantum wells (MQW) in the active region. Using finite-difference time-domain (FDTD) simulations, the sizes of our NW laser cavities are precisely tuned in the radial dimension to optimize the overlap of the desired optical (TE01) mode with the quantum confined gain region for any given lasing wavelength, i.e., InGaAs composition. Importantly, we explore the role of InGaAs-QW/AlGaAs-barrier design and respective growth kinetics on the In incorporation, alloy intermixing, and structural integrity as well as the resulting lasing properties of these NW-QW lasers. Using correlated scanning transmission electron microscopy (STEM), atom probe tomography (APT), and confocal photoluminescence (PL) spectroscopy, we systematically study the growth mediated differences in the quality of the InGaAs QW on the basis of two growth series with variable III/V ratio and temperature. We demonstrate that low-temperature shell growth conditions and GaAs interlayers surrounding the InGaAs QWs enhance In incorporation and reduce alloy intermixing in the MQW structure, yielding tunability of the lasing wavelength over the range from ∼0.8 to ∼1.1 μm. The NW lasers were grown by solid source molecular beam epitaxy (MBE) on Si (111) substrates through random 6293
DOI: 10.1021/acs.nanolett.8b02503 Nano Lett. 2018, 18, 6292−6300
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Nano Letters
Figure 2. (a) Pump-power-dependent lasing spectra of the sample with a nominal In molar fraction of 30% below threshold (black), at threshold (blue) and above threshold (red, yellow, and purple), respectively. Above 0.80 ± 0.06 mJ/cm2, a superlinear lasing peak arises at an energy of ∼1.39 eV. (b) Corresponding L-L curve of the integrated peak intensity as a function of the pump pulse fluence on a double-logarithmic scale (black circles). Corresponding FWHM (blue triangles) as obtained from fitting the lasing peak area shows a distinct decrease of the line width upon exceeding the lasing threshold.
molar fraction was fixed at 30% via a constant group-III supply. All samples were finally capped with a 5 nm thick GaAs shell to prevent oxidation of the active region. All growth stages were performed under constant substrate rotation of 5 rpm (rotations per minute). Figure 1a shows a scanning electron microscopy (SEM) image of as-grown MQW-NW lasers grown at a shell growth temperature of 510 °C and a nominal In molar fraction of 30%. The length of the NWs on this sample varies between ∼6 and 8 μm and the diameter, measured between two opposite {11̅0} side facets, is on average ∼440 nm. Overall, the lengths of NWs from all samples are in the range 6−10 μm, irrespective of the different In molar fractions and shell growth temperatures. In contrast, the diameters differ between ∼360 and ∼480 nm for samples with different In molar fraction due to the differently optimized AlGaAs spacer thickness for each desired emission wavelength (see Supporting Information). The intended inner AlGaAs spacer thickness for the present sample in Figure 1a was 75 nm. The NWs also exhibit a pronounced tip end that represents the crystal facets obtained from crystallization of the Ga droplet after core growth. Thin cross-sectional lamellas were prepared from NWs from the same sample as in Figure 1a using focused ion beam (FIB) milling to analyze quantum wells, barrier layers, and their interfaces via STEM. A typical STEM-HAADF (high angle annular dark field) image of the cross-section of an individual NW is shown in Figure 1b, clearly showing the symmetric and coaxial arrangement of alternating hexagonally shaped QWs and barriers around the core. All layers in the shell structure exhibit thicknesses very close to the nominally expected values, i.e., an AlGaAs spacer thickness of 69 (±13) nm (nominal value of 75 nm), QW thicknesses of 7.9 (±1.1) nm, and AlGaAs/GaAs barrier thicknesses of 8.1 (±0.5) nm. The total diameter of this particular NW cross-section amounts to ∼422 nm. Fluctuations in the InGaAs QW thicknesses as seen in Figure 1b are random and ascribed to slight asymmetries in the radial growth facets, while the nominal growth rates of all consecutive QWs were identical. To better observe the respective layers and their interfaces, Figure 1c depicts a high-resolution STEM image recorded in the corner region of the MQW heterostructure. From the corresponding Z-contrast we can clearly distinguish the AlGaAs barrier, the ∼2 nm thin
GaAs interlayer, and the InGaAs QW. For better orientation, dashed lines in the corresponding colors indicate the interfaces. The interface sharpness appears abrupt to a precision within ∼2−3 monolayers, similar to recent findings in GaAs-AlGaAs core−multishell NW lasers.22 In addition, we also observe dark contrast stripes along the {112̅} corner facets of the AlGaAs barriers, which can be attributed to Al-enrichment as noted in previous studies.30,33 A more detailed element-specific analysis of the individual layers is further shown below in Figure 4. Although the as-grown NW lasers are designed to ultimately operate on a Si photonic platform, where direct coupling of coherent emission into proximal waveguides can be realized,7 we mechanically transferred and dispersed NW lasers onto sapphire templates, which provides sufficient refractive index contrast to enable lasing.16,34 This allows us to obtain a benchmark of the intrinsic lasing properties relative to recently reported NW lasers emitting in the near-IR spectral range.16,34 The lasing characteristics were then investigated on individual NWs subject to pulsed optical excitation in low-temperature confocal photoluminescence microscopy.22,28,29 Hereby, the NWs were probed by optical pulses incident along a direction perpendicular to the NW axis at a wavelength of 780 nm (pulse length 200 fs and 82 MHz repetition rate) with a spot size of ∼1.9 μm. Using the confocal measurement geometry, the emitted light scattered from the NW end facets was collected via a single-mode optical fiber. All measurements presented here were performed in a He-flow cryostat at a nominal temperature of ∼10 K. Figure 2a shows typical pump-powerdependent PL spectra of a NW like that shown in Figure 1 (with nominally 30% In molar fraction in the MQW) as a function of the emitted photon energy. The excitation pump pulse fluence ranges from 0.24 to 2.6 mJ/cm2. A low pump power of 0.24 mJ/cm2 (corresponding to P/Pth = 0.3) produces a broad spectrum (black) dominated by spontaneous emission (SE) around an energy of 1.36 eV. The periodic oscillations are attributed to the feedback of the Fabry−Perotlike nature of the NW cavity.34 With increasing pump power, the SE spectra increase in intensity until the lasing threshold is reached and a superlinear peak emerges at an energy near ∼1.39 eV, accompanied by a clamping of the spontaneous emission. 6294
DOI: 10.1021/acs.nanolett.8b02503 Nano Lett. 2018, 18, 6292−6300
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Figure 3. (a) Normalized lasing emission of NW lasers at 10 K with different nominal In molar fractions in the InGaAs MQW grown at 510 °C. For comparison, NW lasers with binary GaAs MQWs (blue) show lasing emission at an energy of ∼1.57 eV.22 (b) 1D simulations of the transition energies between electron ground state and first heavy hole state showing the dependence on QW thickness and In molar fraction without taking strain into account. The dashed line marks the nominal QW thickness of 8 nm, illustrating the approximate emission energies for the different In molar fractions. (c) Room temperature lasing of the same NW lasers as in (a) for the different In molar fractions in the InGaAs MQWs. The lasing energies are red-shifted by ∼40−90 meV compared to the lasing energies at cryogenic temperatures. (d) Typical L-L curve of the integrated peak intensity as a function of the pump pulse fluence on a double-logarithmic scale of the sample with a nominal In molar fraction of 15%, revealing a threshold of ∼3.6 mJ/cm2.
shown.22 While pure GaAs MQWs lase at ∼1.57 eV (blue),22 increasing the nominal In molar fraction to 15% shifts the dominant lasing peak to lower energy near ∼1.47 eV (red). Further increases in the In molar fraction further red-shifts the lasing energy down to 1.36 eV for an In molar fraction of nominally 40% (green). Additional statistics illustrating the typical peak energy dispersion of a larger number of NW lasers per given sample are further shown in the Supporting Information (Figure S2a). Furthermore, Figure S2b illustrates the corresponding lasing energies and thresholds of all investigated samples. The average lasing thresholds tend to increase from 0.4 to 1.3 mJ/cm2 with increasing In molar fraction. NW lasers from this series were also characterized at room temperature (RT), and all samples evidence clear lasing at RT (Figure 3c) except for the NWs with the highest nominal In molar fraction of 40%. An exemplary L-L curve of the sample with a nominal In molar fraction of 15% is shown in Figure 3d, revealing a lasing threshold of ∼3.6 mJ/cm2 at RT. As depicted in Figure 3c, the lasing energies are red-shifted by ∼40−90 meV compared to the energies at low temperature, which is expected from the Varshni-like37 band gap shrinkage of the gain medium.38 The thresholds at RT are about 3−10 times higher compared to those at cryogenic temperatures, similar to previous observations in coaxial GaAs-AlGaAs MQW-NW lasers.22,39
To investigate the lasing properties in more detail, a doublelogarithmic light-in−light-out (L-L) curve of the integrated peak intensity as a function of the pump pulse fluence (black circles) is plotted in Figure 2b, showing a distinct “s-shape” dependency. A clear transition from SE to amplified spontaneous emission (ASE) and ultimately to lasing is observed with increasing pump power.35 Fitting the integrated intensities with an allometric power law I ∝ Pk, with P being the pump pulse fluence and k the exponent, we find for the ASE regime a value of kASE ∼ 3.45 proving the superlinear increase in intensity. The exponent in the lasing regime is close to the expected value of unity (kLasing ∼ 0.94).36 Linearly plotting the input−output characteristic allows the extraction of the lasing threshold of Pth = 0.80 ± 0.06 mJ/cm2. The transition from the SE to the ASE regime is also reflected by a decreasing full width at half-maximum (FWHM) of the dominant peak from >10 meV below threshold to 380 meV, i.e., >250 nm to the red with the longest lasing wavelength obtained at around 1050 nm. From the respective L-L curves the lasing thresholds were also characterized on a large number of NW lasers. Interestingly, despite the gradual increase in In molar fraction, and hence longer wavelength emission, the lasing threshold does not increase on average within the experimental error in the range between 1.1 and 1.4 mJ/cm2 (see Supporting Information). This behavior is quite different from the first series (shell growth temperature of 510 °C, variable In molar fraction), in which the lasing threshold was found to increase with higher In molar fraction. We believe that the invariant lasing threshold of the second growth series is likely a result of the suppressed alloy intermixing. Further shifting of the lasing emission to longer, Si-transparent wavelengths, will require additional optimization of growth parameters and strategies to avoid plastic relaxation. For example, one should consider straincompensation layers (between core and active region), ultrathin NW cores,33 and alternative barrier materials, e.g., InAlAs, which could be lattice-matched to InGaAs QWs. In conclusion, we investigated the lasing characteristics of individual GaAs-(In,Al)GaAs core−multishell NWs under optical pumping. Specifically, we explored how NW-QW lasing performance is impacted by InGaAs-QW/AlGaAs-barrier design principles and deviations from ideality as influenced by In-incorporation kinetics, alloy intermixing, and structural integrity. Using correlated scanning transmission electron microscopy (STEM), atom probe tomography (APT) and confocal photoluminescence (PL) spectroscopy, the growth mediated effects on the quality of the InGaAs QW were illustrated for two growth series with variable III/V ratio and temperature. Low-temperature shell growth conditions and GaAs interlayers surrounding the InGaAs QWs give rise to enhanced In-incorporation and reduced alloy intermixing in the MQW structure. Clear evidence of lasing (s-shaped LLcurve, SE clamping and line width-narrowing) was found from the InGaAs MQW active region with lasing emission tunable over a wide spectral range. Particularly, the lasing emission was red-shifted by ∼400 meV to 1.18 eV (1050 nm) in GaAs-
Figure 5. (a) Cross-sectional STEM-HAADF image of a NW laser with a nominal In molar fraction of 30%, grown at a shell temperature of 420 °C. (b) EDXS line scan taken along the blue dashed line, revealing more abrupt QW−barrier interfaces and a significantly increased In molar fraction of ∼24 ± 1% in the MQWs. (c) Normalized lasing emission for a constant nominal In molar fraction of 30% grown at different shell growth temperatures and measured at 10 K. The lasing energies show a substantial red shift from initially 1.39 eV for Tshell = 510 °C to 1.34 eV for Tshell = 460 °C and 1.18 eV for Tshell = 420 °C, respectively.
homogeneity. Subsequent EDXS analysis performed along the radial InGaAs-AlGaAs/GaAs heterointerfaces (i.e., blue dashed line across the {11̅0} facet) reveals two marked differences in the alloy compositional profile as compared to the NW laser structure grown at higher temperature (cf. Figure 4b and Figure 5b). First, the characteristic peaks of the Ga elemental profile in the GaAs interlayers are much sharper and more pronounced. This indicates a more abrupt heterointerface between the AlGaAs barriers and adjacent GaAs interlayers, 6298
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(4) Koblmüller, G.; Mayer, B.; Stettner, T.; Abstreiter, G.; Finley, J. J. GaAs-AlGaAs Core-Shell Nanowire Lasers on Silicon: Invited Review. Semicond. Sci. Technol.; IOP Publishing May 1, 2017; p 053001. (5) Mayer, B.; Janker, L.; Loitsch, B.; Treu, J.; Kostenbader, T.; Lichtmannecker, S.; Reichert, T.; Morkötter, S.; Kaniber, M.; Abstreiter, G.; et al. Monolithically Integrated High-β Nanowire Lasers on Silicon. Nano Lett. 2016, 16 (1), 152−156. (6) Kim, H.; Lee, W. J.; Farrell, A. C.; Balgarkashi, A.; Huffaker, D. L. Telecom-Wavelength Bottom-up Nanobeam Lasers on Silicon-onInsulator. Nano Lett. 2017, 17 (9), 5244−5250. (7) Stettner, T.; Kostenbader, T.; Ruhstorfer, D.; Bissinger, J.; Riedl, H.; Kaniber, M.; Koblmüller, G.; Finley, J. J. Direct Coupling of Coherent Emission from Site-Selectively Grown III-V Nanowire Lasers into Proximal Silicon Waveguides. ACS Photonics 2017, 4 (10), 2537. (8) Johnson, J. C.; Choi, H.-J.; Knutsen, K. P.; Schaller, R. D.; Yang, P.; Saykally, R. J. Single Gallium Nitride Nanowire Lasers. Nat. Mater. 2002, 1 (2), 106−110. (9) Li, K. H.; Liu, X.; Wang, Q.; Zhao, S.; Mi, Z. Ultralow-Threshold Electrically Injected AlGaN Nanowire Ultraviolet Lasers on Si Operating at Low Temperature. Nat. Nanotechnol. 2015, 10 (2), 140−144. (10) Gradečak, S.; Qian, F.; Li, Y.; Park, H.-G.; Lieber, C. M. GaN Nanowire Lasers with Low Lasing Thresholds. Appl. Phys. Lett. 2005, 87, 173111. (11) Johnson, J. C.; Yan, H.; Yang, P.; Saykally, R. J. Optical Cavity Effects in ZnO Nanowire Lasers and Waveguides. J. Phys. Chem. B 2003, 107 (34), 8816−8828. (12) Chu, S.; Wang, G.; Zhou, W.; Lin, Y.; Chernyak, L.; Zhao, J.; Kong, J.; Li, L.; Ren, J.; Liu, J. Electrically Pumped Waveguide Lasing from ZnO Nanowires. Nat. Nanotechnol. 2011, 6 (8), 506−510. (13) Geburt, S.; Thielmann, A.; Röder, R.; Borschel, C.; Mcdonnell, A.; Kozlik, M.; Uhnel, J.; Sunter, K. A.; Capasso, F.; Ronning, C. Low Threshold Room-Temperature Lasing of CdS Nanowires. Nanotechnology 2012, 23, 365204. (14) Liu, Z.; Yin, L.; Ning, H.; Yang, Z.; Tong, L.; Ning, C. Z. Dynamical Color-Controllable Lasing with Extremely Wide Tuning Range from Red to Green in a Single Alloy Nanowire Using Nanoscale Manipulation. Nano Lett. 2013, 13 (10), 4945−4950. (15) Saxena, D.; Mokkapati, S.; Parkinson, P.; Jiang, N.; Gao, Q.; Tan, H. H.; Jagadish, C. Optically Pumped Room-Temperature GaAs Nanowire Lasers. Nat. Photonics 2013, 7 (12), 963−968. (16) Mayer, B.; Rudolph, D.; Schnell, J.; Morkötter, S.; Winnerl, J.; Treu, J.; Müller, K.; Bracher, G.; Abstreiter, G.; Koblmüller, G.; et al. Lasing from Individual GaAs-AlGaAs Core-Shell Nanowires up to Room Temperature. Nat. Commun. 2013, 4, 2931. (17) Gao, Q.; Saxena, D.; Wang, F.; Fu, L.; Mokkapati, S.; Guo, Y.; Li, L.; Wong-Leung, J.; Caroff, P.; Tan, H. H.; et al. Selective-Area Epitaxy of Pure Wurtzite InP Nanowires: High Quantum Efficiency and Room-Temperature Lasing. Nano Lett. 2014, 14, 5206−5211. (18) Ren, D.; Ahtapodov, L.; Nilsen, J. S.; Yang, J.; Gustafsson, A.; Huh, J.; Conibeer, G. J.; Van Helvoort, A. T. J.; Fimland, B. O.; Weman, H. Single-Mode Near-Infrared Lasing in a GaAsSb-Based Nanowire Superlattice at Room Temperature. Nano Lett. 2018, 18 (4), 2304−2310. (19) Chen, R.; Ng, K. W.; Ko, W. S.; Parekh, D.; Lu, F.; Tran, T. T. D.; Li, K.; Chang-Hasnain, C. Nanophotonic Integrated Circuits from Nanoresonators Grown on Silicon. Nat. Commun. 2014, 5, 4325. (20) Arakawa, Y. Multidimensional Quantum Well Laser and Temperature Dependence of Its Threshold Current. Appl. Phys. Lett. 1982, 40 (11), 939. (21) Tatebayashi, J.; Kako, S.; Ho, J.; Ota, Y.; Iwamoto, S.; Arakawa, Y. Room-Temperature Lasing in a Single Nanowire with Quantum Dots. Nat. Photonics 2015, 9 (8), 501−505. (22) Stettner, T.; Zimmermann, P.; Loitsch, B.; Döblinger, M.; Regler, A.; Mayer, B.; Winnerl, J.; Matich, S.; Riedl, H.; Kaniber, M. Coaxial GaAs-AlGaAs Core-Multishell Nanowire Lasers with Epitaxial Gain Control. Appl. Phys. Lett. 2016, 108 (1), 011108.
InGaAs MQW NW lasers, compared to pure GaAs-AlGaAs MQW NW lasing structures. These results pave the way for future all-optical on-chip communication platform at a favorable low-loss range in the telecommunication wavelength regime.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.nanolett.8b02503. Details on FDTD simulations, MBE growth parameters, NW length and diameter statistics, detailed lasing statistics, 1D strain simulations, STEM-EDXS data analysis, additional APT data, and shell growth temperature series (PDF)
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AUTHOR INFORMATION
Corresponding Authors
*T. Stettner. E-mai:
[email protected]. *G. Koblmüller. E-mail:
[email protected]. ORCID
T. Stettner: 0000-0002-6294-4731 M. O. Hill: 0000-0002-7663-7986 L. J. Lauhon: 0000-0001-6046-3304 G. Koblmüller: 0000-0002-7228-0158 Author Contributions
The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported financially by the Deutsche Forschungsgemeinschaft (DFG) via Project Grants FI 947/41 and KO 4005/7-1, the Nanosystems Initiative Munich (NIM), the International Graduate School of Science and Engineering (TUM-IGSSE), and the IBM International Ph.D. Fellowship Program. M.O.H. and L.J.L. further acknowledge support by NSF DMR-1611341. M.O.H. acknowledges support of the NSF GRFP. Atom probe tomography was performed at the Northwestern University Center for AtomProbe Tomography (NUCAPT). The LEAP tomograph at NUCAPT was purchased and upgraded with grants from the NSF-MRI (DMR-0420532) and ONR-DURIP (N000140400798, N00014-0610539, N00014-0910781, N000141712870) programs. NUCAPT received support from the MRSEC program (NSF DMR-1720139) at the Materials Research Center, the SHyNE Resource (NSF ECCS1542205), and the Initiative for Sustainability and Energy (ISEN) at Northwestern University.
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REFERENCES
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DOI: 10.1021/acs.nanolett.8b02503 Nano Lett. 2018, 18, 6292−6300
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Nano Letters
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DOI: 10.1021/acs.nanolett.8b02503 Nano Lett. 2018, 18, 6292−6300
