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16 Jan 2012

Volume 100, Issue 3, Articles (03xxxx)

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Appl. Phys. Lett. 100, 033109 (2012); http://dx.doi.org/10.1063/1.3664636 (3 pages)

Sang H. Yun, Hyung-Seok Lee, Young Ha Kwon, Mats Göthelid, Sang Mo Koo, Lars Wågberg, Ulf O. Karlsson, and Jan Linnros
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A tapered parallel-plate-waveguide probe for THz near-field reflection imaging

Jingbo Liu, Rajind Mendis, Daniel M. Mittleman, and Naokazu Sakoda

Appl. Phys. Lett. 100, 031101 (2012); http://dx.doi.org/10.1063/1.3677678 (3 pages) | Cited 5 times

Online Publication Date: 17 January 2012

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We demonstrate a broad-band low-loss THz near-field imaging technique based on a tapered parallel-plate waveguide. This technique works in a reflection geometry, which avoids the problem of low energy throughput due to the impedance mismatch and consequently limited spatial resolution, in the transmission geometry. Images reconstructed by the filtered-back-projection algorithm are able to resolve features of size ∼100 μm using radiation with an average wavelength of 1.5 mm.
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84.40.-x Radiowave and microwave (including millimeter wave) technology
42.30.Va Image forming and processing
42.30.Wb Image reconstruction; tomography

Self-assembled broadband plasmonic nanoparticle arrays for sensing applications

R. Verre, K. Fleischer, O. Ualibek, and I. V. Shvets

Appl. Phys. Lett. 100, 031102 (2012); http://dx.doi.org/10.1063/1.3674982 (3 pages) | Cited 4 times

Online Publication Date: 17 January 2012

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Highly ordered noble metal nanoparticle (NP) arrays are produced using a glancing angle deposition on stepped substrates. The versatility of the technique is demonstrated by depositing different metals, resulting in shifts of the resonance positions. The behaviour of the NP arrays grown is predicted by a dipolar model, and it is measured using reflectance anisotropy spectroscopy (RAS). Fine tuning of the resonances can be finally realised by selecting the deposition parameters. The combined application of both RAS and deposition at glancing angles provides a unique tool to grow NP arrays with the tunable plasmonic resonances in the entire visible range.
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81.16.Dn Self-assembly
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.66.Bz Metals and metallic alloys

Low-voltage driven visible and infrared electroluminescence from light-emitting device based on Er-doped TiO2/p+-Si heterostructure

Yang Yang, Lu Jin, Xiangyang Ma, and Deren Yang

Appl. Phys. Lett. 100, 031103 (2012); http://dx.doi.org/10.1063/1.3678026 (4 pages) | Cited 5 times

Online Publication Date: 18 January 2012

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We report on visible and infrared electroluminescence (EL) from the light-emitting device based on Er-doped TiO2/p+-Si heterostructure. Under a forward bias voltage as low as 5.5 V, the device emits ∼1540 nm infrared light and visible light peaking at 522, 553, 564, and 663 nm, respectively, which are originated from Er3+ intra-4f transitions. It is found that the existence of sufficient oxygen vacancies in TiO2 is critical for triggering the Er-related EL. Furthermore, the energy transfer from the oxygen-vacancy-related excitons in TiO2 matrix to Er3+ ions is supposed to be responsible for the above-mentioned EL.
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85.60.Jb Light-emitting devices

Fabrication of nanometer-size structures in metal thin films using femtosecond laser Bessel beams

B. Yalizay, T. Ersoy, B. Soylu, and S. Akturk

Appl. Phys. Lett. 100, 031104 (2012); http://dx.doi.org/10.1063/1.3678030 (3 pages) | Cited 3 times

Online Publication Date: 18 January 2012

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We report nanometer-scale fabrication on metal thin films using ablation by femtosecond laser pulses, with Bessel beam profiles. Choosing the laser fluence around ablation threshold allows control of the structure size below the diffraction limit. We show that using Bessel beams has several advantages. Bessel beams have focal spot sizes insensitive to longitudinal position, which significantly relaxes alignment constraints. Tighter foci are easier to generate, less costly, and less prone to aberrations. Scaling the method to shorter wavelengths, and hence increasing the resolution is also straightforward. By using the proposed method, we generate structures with resolution below 200 nm.
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42.62.-b Laser applications
42.82.Cr Fabrication techniques; lithography, pattern transfer
68.55.-a Thin film structure and morphology
81.16.-c Methods of micro- and nanofabrication and processing

Improvement of hole injection and electron overflow by a tapered AlGaN electron blocking layer in InGaN-based blue laser diodes

Wei Yang, Ding Li, Ningyang Liu, Zhao Chen, Lei Wang, Lei Liu, Lei Li, Chenghao Wan, Weihua Chen, Xiaodong Hu, and Weimin Du

Appl. Phys. Lett. 100, 031105 (2012); http://dx.doi.org/10.1063/1.3678197 (5 pages) | Cited 2 times

Online Publication Date: 18 January 2012

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We studied the influence of a tapered AlGaN electron blocking layer (EBL) with step-graded aluminum composition on hole injection and electron overflow effects in InGaN-based laser diodes (LDs) theoretically. Schrödinger-Poisson self-consistent method together with transfer matrix method was applied to calculate carrier distribution and transport properties for both electrons and holes in tapered EBL and conventional EBL. The results indicate that the new structure favors the tunneling of low energy holes from the p-side to the active region. Meanwhile, more uniform carrier distribution and better balance between electrons and holes are obtained for the tapered structure by proper modification of band diagrams. An advanced device simulation shows the elimination of electron overflow even at a current of 180 mA in the LD with tapered EBL. Decrease of threshold current density from 2.0 kA/cm2 to 1.6 kA/cm2 is benefited from the more uniform local gain profile.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Ultrafast all-optical tunable Fano resonance in nonlinear ferroelectric photonic crystals

Yingbo Zhang, Xiaoyong Hu, Yulan Fu, Hong Yang, and Qihuang Gong

Appl. Phys. Lett. 100, 031106 (2012); http://dx.doi.org/10.1063/1.3678184 (4 pages) | Cited 6 times

Online Publication Date: 19 January 2012

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We report an ultrafast all-optical tunable Fano resonance in a nonlinear ferroelectric photonic crystal made of polycrystal lithium niobate, which provides a large nonlinear susceptibility because of strong quantum size effect of nanoscale crystal grains. The femtosecond pump and probe method is adopted to measure the tunability of the Fano resonance based on the nonlinear optical Kerr effect. A 37-nm shift in the Fano resonance wavelength is obtained under excitation of a 30 MW/cm2 pump laser. An ultrafast response time of 43 ps is achieved due to fast relaxation dynamics of bound electrons in polycrystal lithium niobate.
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42.70.Qs Photonic bandgap materials
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

High-power laterally coupled distributed-feedback GaSb-based diode lasers at 2 μm wavelength

Siamak Forouhar, Ryan M. Briggs, Clifford Frez, Kale J. Franz, and Alexander Ksendzov

Appl. Phys. Lett. 100, 031107 (2012); http://dx.doi.org/10.1063/1.3678187 (4 pages) | Cited 3 times

Online Publication Date: 19 January 2012

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We report on GaSb-based laterally coupled distributed-feedback (DFB) diode lasers designed to operate at wavelengths near 2.05 μm. Second-order Bragg gratings were etched alongside narrow ridge waveguides to enable single-mode DFB operation in 2-mm-long laser diodes. At a heat-sink temperature of 10 °C, the lasers emit more than 40 mW continuous-wave in a single longitudinal mode, while increasing the current beyond 300 mA results in multimode operation due to spectral shifting of the laser gain with respect to the peak grating reflectivity. At −10 °C, we observe DFB operation at higher current, with single-facet emission exceeding 80 mW.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Thermal resistance reduction in high power superluminescent diodes by using active multi-mode interferometer

Zhigang Zang, Keisuke Mukai, Paolo Navaretti, Marcus Duelk, Christian Velez, and Kiichi Hamamoto

Appl. Phys. Lett. 100, 031108 (2012); http://dx.doi.org/10.1063/1.3678188 (4 pages) | Cited 30 times

Online Publication Date: 19 January 2012

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Low thermal resistance of high power superluminescent diodes (SLEDs) by using active multi-mode interferometer (active-MMI) is presented in this paper. The active layer temperature evaluation demonstrates that the power saturation mechanism in active-MMI SLED is heat for the first time. Low thermal resistance of 4.83 K/W in active-MMI SLEDs leads to a high power of 115 mW. Moreover, the effect of the active area size on the output power is demonstrated both experimentally and theoretically. Good agreement between the theoretical and experimental results indicates that active-MMI configuration is a new design in support of efficient heat dissipation and thermal resistance reduction for SLEDs.
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85.60.Jb Light-emitting devices

Semiconductor disk laser at 2.05 μm wavelength with <100 kHz linewidth at 1 W output power

Sebastian Kaspar, Marcel Rattunde, Tino Töpper, Christian Manz, Klaus Köhler, and Joachim Wagner

Appl. Phys. Lett. 100, 031109 (2012); http://dx.doi.org/10.1063/1.3675637 (3 pages) | Cited 3 times

Online Publication Date: 19 January 2012

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We report on an optically pumped single-mode GaSb-based semiconductor disk laser (SDL) emitting at 2.05 μm at an output power of 960 mW (1100 mW) with a side-mode suppression of better than 30 dB (20 dB). A linewidth of 60 kHz (sampling time: 100 μs) was measured at an output power of 960 mW. This improvement in output power over previous reports, which was achieved via a careful design of the SDL cavity paying close attention to the spatial overlap between cavity mode and pump spot, makes this class of SDL particularly attractive for remote sensing and optical free-space communication.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Microwire (Mg,Zn)O/ZnO and (Mg,Zn)O/(Cd,Zn)O non-polar quantum well heterostructures for cavity applications

C. P. Dietrich, M. Lange, M. Stölzel, and M. Grundmann

Appl. Phys. Lett. 100, 031110 (2012); http://dx.doi.org/10.1063/1.3678594 (4 pages) | Cited 3 times

Online Publication Date: 19 January 2012

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Pulsed-laser deposited, non-polar MgxZn1−xO/ZnO and MgxZn1−xO/Zn1−yCdyO quantum well heterostructures were fabricated in radial direction on ZnO microwires with well-defined hexagonal cross section. Optical resonances modulate room-temperature luminescence spectra for all fabricated heterostructures demonstrating their applicability as microcavities. Quantum confinement was proven by time-integrated and time-resolved luminescence. The ZnO quantum well emission was tuned between 3.76 and 3.35 eV by adjusting the well thickness and barrier composition. In order to further reduce the QW emission energy, active Zn1−yCdyO quantum wells in MgxZn1−xO barriers were grown emitting between 3.07 and 2.70 eV for different well thicknesses but fixed barrier composition.
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42.79.-e Optical elements, devices, and systems
42.82.Cr Fabrication techniques; lithography, pattern transfer
06.60.Vz Workshop procedures (welding, machining, lubrication, bearings, etc.)

Room temperature, continuous wave lasing in microcylinder and microring quantum dot laser diodes

M. Munsch, J. Claudon, N. S. Malik, K. Gilbert, P. Grosse, J.-M. Gérard, F. Albert, F. Langer, T. Schlereth, M. M. Pieczarka, S. Höfling, M. Kamp, A. Forchel, and S. Reitzenstein

Appl. Phys. Lett. 100, 031111 (2012); http://dx.doi.org/10.1063/1.3678031 (4 pages) | Cited 1 time

Online Publication Date: 20 January 2012

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We demonstrate room temperature, continuous wave lasing of laser diodes based on AlGaAs whispering gallery mode (WGM) resonators (microcylinder and microring) embedding a quantum dot (QD) active layer. Using InGaAlAs QDs, high-Q (>60 000) lasing modes are observed around 910 nm, up to 50 °C. Lasing with similar performance is obtained around 1230 nm, using InAs QDs. Furthermore, we show that the current injection in the active part of the device is improved in ring resonators, leading to threshold currents of approximately 4 mA for a device with 80 μm diameter. This geometry also suppresses WGMs with a high radial order, thus simplifying the lasing spectra. In these conditions, stable single-mode and two-color lasing can be obtained.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Advantages of blue InGaN light-emitting diodes with InGaN-AlGaN-InGaN barriers

Yen-Kuang Kuo, Tsun-Hsin Wang, and Jih-Yuan Chang

Appl. Phys. Lett. 100, 031112 (2012); http://dx.doi.org/10.1063/1.3678341 (3 pages) | Cited 3 times

Online Publication Date: 20 January 2012

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Efficiency enhancement of the blue InGaN light-emitting diodes (LEDs) with InGaN-AlGaN-InGaN barriers is studied numerically. The energy band diagrams, carrier concentrations in quantum wells, radiative recombination rate in active region, light-current performance curves, and internal quantum efficiency are investigated. The simulation results suggest that the blue InGaN/InGaN-AlGaN-InGaN LED has better performance over its conventional InGaN/GaN and InGaN/InGaN counterparts due to the appropriately modified energy band diagrams, which are caused mainly by the reduced polarization charges at the interface between the well and barrier.
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85.60.Jb Light-emitting devices

Enhancement of light-extraction efficiency of SiNx light emitting devices through a rough Ag island film

Feng Wang, Dongsheng Li, Deren Yang, and Duanlin Que

Appl. Phys. Lett. 100, 031113 (2012); http://dx.doi.org/10.1063/1.3678632 (4 pages) | Cited 11 times

Online Publication Date: 20 January 2012

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Based on an ITO/Ag/SiNx/p+-Si/Al structure, a significant enhancement of the external quantum efficiency was achieved compared with the device without Ag island film. Analysis showed that the increase of the light-extraction efficiency resulted from the surface roughening of ITO electrode has a main contribution to this enhancement. The increase of the internal quantum efficiency induced by the enhancement of spontaneous emission rate and the carrier injection level also has an instructive contribution. Our results demonstrate that localized surface plasmons enhanced SiNx-based light emitting devices show great promise for the development of efficiency Si-based optical device.
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85.60.Jb Light-emitting devices
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