Rafal Dylewicz

Publications

• 3.28

  Impact points

  Fast saturable absorption and 10 GHz wavelength conversion in Al-quaternary multiple quantum wells.

  Richard P Green, Mohsin Haji, Lianping Hou, Gabor Mezosi, Rafal Dylewicz, Anthony E Kelly

  Optics express. 05/2011; 19(10):9737-43.

  We measured the absorption recovery times in reverse biased AlInGaAs multiple quantum well material designed to emit at around 1.5 μm wavelength. Absorption recovery times as low as 2.5 ps were found at -4V bias, with values below 5 ps consistently found for biases above 3 V. The short absorption re... [more] We measured the absorption recovery times in reverse biased AlInGaAs multiple quantum well material designed to emit at around 1.5 μm wavelength. Absorption recovery times as low as 2.5 ps were found at -4V bias, with values below 5 ps consistently found for biases above 3 V. The short absorption recovery times obtained under reverse bias were confirmed by using cross-absorption modulation in the material to demonstrate wavelength conversion of a 10 GHz pulse train, showing both up and down conversion of the incident pulses.
• 3.14

  Impact points

  Nanotexturing of GaN light-emitting diode material through mask-less dry etching.

  Rafal Dylewicz, Ali Z Khokhar, Radoslaw Wasielewski, Piotr Mazur, Faiz Rahman

  Nanotechnology. 02/2011; 22(5):055301.

  We describe a new technique for random surface texturing of a gallium nitride (GaN) light-emitting diode wafer through a mask-less dry etch process. This involves depositing a sub-monolayer film of silica nanospheres (typical diameter of 200 nm) and then subjecting the coated wafer to a dry etch pro... [more] We describe a new technique for random surface texturing of a gallium nitride (GaN) light-emitting diode wafer through a mask-less dry etch process. This involves depositing a sub-monolayer film of silica nanospheres (typical diameter of 200 nm) and then subjecting the coated wafer to a dry etch process with enhanced physical bombardment. The silica spheres acting as nanotargets get sputtered and silica fragments are randomly deposited on the GaN epi-layer. Subsequently, the reactive component of the dry etch plasma etches through the exposed GaN surface. Silica fragments act as nanoparticles, locally masking the underlying GaN. The etch rate is much reduced at these sites and consequently a rough topography develops. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) inspections show that random topographic features at the scale of a few tens of nanometres are formed. Optical measurements using angle-resolved photoluminescence show that GaN light-emitting diode material thus roughened has the capability to extract more light from within the epilayers.

• Conductive polymers for advanced micro- and nano-fabrication processes - Japanese version

  R. Dylewicz, N. Klauke, J. Cooper, F. Rahman

  Material Matters - Methods for Nanopatterning and Lithography, Sigma-Aldrich newsletter (http://www.sigmaaldrich.com/materials-science/learning-center/material-matters.html). 2011; 6(1):18-21. 01/2011;

  Conducting polymers such as polyaniline, polythiophene and polyfluorenes are now much in the spotlight for their applications in organic electronics and optoelectronics. Such materials are used, for example, in making organic thin-film transistors and light-emitting diodes. Here, we present a novel ... [more] Conducting polymers such as polyaniline, polythiophene and polyfluorenes are now much in the spotlight for their applications in organic electronics and optoelectronics. Such materials are used, for example, in making organic thin-film transistors and light-emitting diodes. Here, we present a novel application of conductive polymer thin films – for use as charge dissipation layers for state-of-the-art patterning techniques, i.e., electron-beam lithography (EBL) and focused ion beam (FIB) etching, on demanding substrates. The ability of thin polythiophene layers to dissipate accumulated charge in electron-beam lithography of wide bandgap semiconductors, e.g., zinc oxide and gallium nitride, as well as for focused ion beam patterning of glass is demonstrated here.

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• Increased latitude of electron-beam lithography processes on GaN with conductive polymer charge dissipation layer

  R. Dylewicz, S. Lis, S. Patela, F. Rahman

  9th International Conference on Nitride Semiconductors (ICNS-9), Glasgow, United Kingdom; 01/2011

  In order to dissipate charge during EBL process PSS:PEDOT conductive polymer was used instead of thin metal layer. The ability to expose dense and high-resolution patterns,e.g. photonic crystals, by EBL method using polymer is presented. Feature size dependency on exposure dose is shown as well.... [more] In order to dissipate charge during EBL process PSS:PEDOT conductive polymer was used instead of thin metal layer. The ability to expose dense and high-resolution patterns,e.g. photonic crystals, by EBL method using polymer is presented. Feature size dependency on exposure dose is shown as well.

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• SiCl4/SF6/Ar-based RIE dry etching with single HSQ resist mask for fabrication of photonic nano-devices in GaN

  R. Dylewicz, L. Zhao, S. Lis, S. Patela, F. Rahman

  9th International Conference on Nitride Semiconductors (ICNS-9), Glasgow, United Kingdom; 01/2011

  RIE dry etching using SiCl4/SF6/Ar gas mixture with a single HSQ resist mask for a fabrication of photonic nano-devices in GaN, e.g. photonic crystal waveguides, is presented. Two types of photonic crystal waveguides were fabricated in half-micron thick GaN layers, with size of features below 500 nm... [more] RIE dry etching using SiCl4/SF6/Ar gas mixture with a single HSQ resist mask for a fabrication of photonic nano-devices in GaN, e.g. photonic crystal waveguides, is presented. Two types of photonic crystal waveguides were fabricated in half-micron thick GaN layers, with size of features below 500 nm. Low sidewall roughness and precise transfer of pattern from HSQ mask to GaN layer were achieved in the experiment.

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• Nanostructured antireflection layers on GaN for enhancing light extraction from light-emitting diodes

  R. Dylewicz, A. Z. Khokhar, R. Wasielewski, P. Mazur, F. Rahman

  European Conference on Surface Science (ECOSS), Wroclaw, Poland; 01/2011

  Light-emitting semiconductor devices often suffer from the mismatch of refractive index between the semiconductor material and the outside medium, which prevents a large fraction of generated light from escaping outside planar waveguide. Here we describe a novel technique for achieving refractive in... [more] Light-emitting semiconductor devices often suffer from the mismatch of refractive index between the semiconductor material and the outside medium, which prevents a large fraction of generated light from escaping outside planar waveguide. Here we describe a novel technique for achieving refractive index matching between GaN–a widely used semiconductor for making blue and ultraviolet LEDs–and ambient air. Our technique is based on creating a graded refractive index zone at the top surface of GaN LED wafer by creating a meso-porous surface. In non-lithographic pattern formation GaN surface is coated with sub-monolayer coverage of silica nano-spheres and then treated by a plasma discharge in a reactive ion etching (RIE) tool.

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• 0.66

  Impact points

  Simulations of nanograting-assisted light coupling in GaN planar waveguide

  R. Dylewicz, R. A. Hogg, R. Airey, R. Paszkiewicz, P. Bientsman, S. Patela

  Optical and Quantum Electronics. 01/2011; 42:619-629.

  The numerical simulations of nanogratings integrated with gallium nitride (GaN) planar waveguides as well as the experimental in-coupling results are presented. A simulation tool based on the eigenmode expansion method and advanced boundary conditions provided a rigorous model of 400-nm-period grati... [more] The numerical simulations of nanogratings integrated with gallium nitride (GaN) planar waveguides as well as the experimental in-coupling results are presented. A simulation tool based on the eigenmode expansion method and advanced boundary conditions provided a rigorous model of 400-nm-period grating couplers. A full-vectorial Maxwell solver allowed performing a number of simulations with varying grating parameters, where coupling efficiency, reflection and transmission characteristics of device were calculated. Gratings with different etch depths and arbitrary shapes were simulated using a staircase approximation, with an optimized number of steps per single slope. For the first time, an impact of dry etch processing on GaN coupler efficiency was evaluated, due to the inclusion of the sloped sidewalls, with regard to the technological constrains. Finally, the experimental results in the visible spectrum region (λ = 633 nm), for 400-nm-deep gratings etched in GaN waveguide, were presented together with theoretical data for binary and trapezoidal profiles of a grating, for different optical mode profiles (TE0 ÷ TE3 modes).

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• 10-GHz mode-locked extended cavity laser integrated with surface-etched DBR fabricated by quantum-well intermixing

  L. Hou, M. Haji, R. Dylewicz, B. Qiu, A. C. Bryce

  IEEE Photonics Technology Letters. 01/2011; 23:82-84.

  10 GHz passively mode-locked AlGaInAs/InP 1.55 μm extended cavity lasers integrated with optimized surface-etched distributed Bragg mirrors have been fabricated. Quantum well intermixing process was used to provide low-absorption loss gratings with accurate wavelength control. The lasers produce 2.9... [more] 10 GHz passively mode-locked AlGaInAs/InP 1.55 μm extended cavity lasers integrated with optimized surface-etched distributed Bragg mirrors have been fabricated. Quantum well intermixing process was used to provide low-absorption loss gratings with accurate wavelength control. The lasers produce 2.99 ps sech2-pulses with TBP of 0.51.

• Influence of nanocrystalline structure and composition on hardness of thin films based on TiO2

  D. Kaczmarek, D. Wojcieszak, J. Domaradzki, E. Prociow, F. Placido, S. Lapp, R. Dylewicz

  Central European Journal of Physics. 01/2011; 9(2):349-353.

  In this work, the influence of Tb-doping on structure, and especially hardness of nanocrystalline TiO2 thin films, has been described. Thin films were formed by a high-energy reactive magnetron sputtering process in a pure oxygen atmosphere. Undoped TiO2-matrix and TiO2:Tb (2 at. % and 2.6 at. %) th... [more] In this work, the influence of Tb-doping on structure, and especially hardness of nanocrystalline TiO2 thin films, has been described. Thin films were formed by a high-energy reactive magnetron sputtering process in a pure oxygen atmosphere. Undoped TiO2-matrix and TiO2:Tb (2 at. % and 2.6 at. %) thin films, had rutile structure with crystallite sizes below 10 nm. The high-energy process produces nanocrystalline, homogenous films with a dense and close packed structure, that were confirmed by X-ray diffraction patterns and micrographs from a scanning electron microscope. Investigation of thin film hardness was performed with the aid of a nanoindentation technique. Results of measurements have shown that the hardness of all manufactured nanocrystalline films is above 10 GPa. In the case of undoped TiO2 matrix, the highest hardness value was obtained (14.3 GPa), while doping with terbium results in hardness decreasing down to 12.7 GPa and 10.8 GPa for TiO2:(2 at. % Tb) and TiO2:(2.6 at. % Tb) thin films, respectively. Incorporation of terbium into TiO2-matrix also allows modification of the elastic properties of the films.

• Conductive polymers for advanced micro- and nano-fabrication processes

  R. Dylewicz, N. Klauke, J. Cooper, F. Rahman

  Material Matters - Methods for Nanopatterning and Lithography, Sigma-Aldrich newsletter (http://www.sigmaaldrich.com/materials-science/learning-center/material-matters.html). 01/2011; 6(1):18-21.

  Conducting polymers such as polyaniline, polythiophene and polyfluorenes are now much in the spotlight for their applications in organic electronics and optoelectronics. Such materials are used, for example, in making organic thin-film transistors and light-emitting diodes. Here, we present a novel ... [more] Conducting polymers such as polyaniline, polythiophene and polyfluorenes are now much in the spotlight for their applications in organic electronics and optoelectronics. Such materials are used, for example, in making organic thin-film transistors and light-emitting diodes. Here, we present a novel application of conductive polymer thin films – for use as charge dissipation layers for state-of-the-art patterning techniques, i.e., electron-beam lithography (EBL) and focused ion beam (FIB) etching, on demanding substrates. The ability of thin polythiophene layers to dissipate accumulated charge in electron-beam lithography of wide bandgap semiconductors, e.g., zinc oxide and gallium nitride, as well as for focused ion beam patterning of glass is demonstrated here.

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• Conductive polymers offer charge dissipation in GaN and ZnO sample processing

  R. Dylewicz, F. Rahman

  Compound Semiconductor Magazine. 01/2011; 17(2):25-27.

  Conducting polymers such as polythiophenes promise to replace metallic films for charge dissipation in semiconductor processing. This switch should provide ease of use and deliver results of unprecedented quality.... [more] Conducting polymers such as polythiophenes promise to replace metallic films for charge dissipation in semiconductor processing. This switch should provide ease of use and deliver results of unprecedented quality.

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• AlGaInAs mode-locked lasers for ultrashort pulse harmonic mode locking

  L. Hou, E.A. Avrutin, R. Dylewicz, M. Haji, B. Qiu, A.C. Bryce

  13th International Conference on Transparent Optical Networks (ICTON) 2011, IEEE Proceedings, Stockholm, Sweden; 01/2011

  Monolithic AlInGaAs compound-cavity lasers for harmonic ML at multi-GHz frequencies have been fabricated and assessed. Optical pulses of ~ 1 ps long at 160 GHz have been obtained. The optimal cavity and reflector design has been investigated experimentally and theoretically.... [more] Monolithic AlInGaAs compound-cavity lasers for harmonic ML at multi-GHz frequencies have been fabricated and assessed. Optical pulses of ~ 1 ps long at 160 GHz have been obtained. The optimal cavity and reflector design has been investigated experimentally and theoretically.

• 40 GHz AlGaInAs/InP 1.55 micron passively mode-locked laser with low divergence angle and timing jitter

  L. Hou, J. Akbar, M. Haji, P. Stolarz, R. Dylewicz, A. Kelly, M. Sorel, J. Marsh, A.C. Bryce, B. Qiu

  Conference on Lasers and Electro-Optics (CLEO) - Laser Applications to Photonic Applications, Baltimore, USA; 01/2011

  A novel 40 GHz passively mode-locked AlGaInAs/InP 1.55 micron laser was demonstrated with low divergence angle, timing jitter of 440 fs (100 Hz - 100 MHz), and RF linewidth of 25 kHz.... [more] A novel 40 GHz passively mode-locked AlGaInAs/InP 1.55 micron laser was demonstrated with low divergence angle, timing jitter of 440 fs (100 Hz - 100 MHz), and RF linewidth of 25 kHz.
• 3.06

  Impact points

  160 GHz harmonic mode-locked AlGaInAs 1.55 μm strained quantum-well compound-cavity laser.

  Lianping Hou, Mohsin Haji, Rafal Dylewicz, Piotr Stolarz, Bocang Qiu, Eugene A Avrutin, A Catrina Bryce

  Optics letters. 12/2010; 35(23):3991-3.

  We characterized the reflectivity and the modal discrimination of intracavity reflectors (ICRs) with different numbers of slots and presented harmonic mode-locking operation of a monolithic semiconductor laser comprising a compound cavity formed by a single deeply etched slot ICR fabricated from 1.5... [more] We characterized the reflectivity and the modal discrimination of intracavity reflectors (ICRs) with different numbers of slots and presented harmonic mode-locking operation of a monolithic semiconductor laser comprising a compound cavity formed by a single deeply etched slot ICR fabricated from 1.55 μm AlGaInAs strained quantum well material. Gaussian pulses were generated at a 161.8 GHz repetition rate with a pulse duration of 1.67 ps and a time-bandwidth product of 0.81.
• 1.82

  Impact points

  Monolithic 45-GHz Mode-Locked Surface-Etched DBR Laser Using Quantum-Well Intermixing Technology

  Lianping Hou, M. Haji, R. Dylewicz, Bocang Qiu, A.C. Bryce

  Photonics Technology Letters, IEEE. 08/2010;

  The 45-GHz passively mode-locked AlGaInAs-InP 1.55- m lasers integrated with surface-etched distributed Bragg mirrors have been fabricated. Quantum-well intermixing was used to provide low absorption loss gratings with accurate wavelength control. The lasers produce 3.6-ps Gaussian pulses with time-... [more] The 45-GHz passively mode-locked AlGaInAs-InP 1.55- m lasers integrated with surface-etched distributed Bragg mirrors have been fabricated. Quantum-well intermixing was used to provide low absorption loss gratings with accurate wavelength control. The lasers produce 3.6-ps Gaussian pulses with time-bandwidth product of 0.57.
• 3.28

  Impact points

  Impact of titanium adhesion layers on the response of arrays of metallic split-ring resonators (SRRs).

  Basudev Lahiri, Rafal Dylewicz, Richard M De La Rue, Nigel P Johnson

  Optics express. 05/2010; 18(11):11202-8.

  At higher frequencies (visible and infrared) both the dimensions and the individual metal properties play an important role in determining the resonant response of arrays of SRRs. As a result, a substantial difference between the responses of gold- and Al-based SRR arrays has been observed. Addition... [more] At higher frequencies (visible and infrared) both the dimensions and the individual metal properties play an important role in determining the resonant response of arrays of SRRs. As a result, a substantial difference between the responses of gold- and Al-based SRR arrays has been observed. Additionally, deposition of gold SRRs onto a substrate typically involves the use of an additional adhesion layer. Titanium (Ti) is the most common adhesive thin-film material used to attach gold onto dielectric/semiconductor substrates. In this paper we investigate the impact of the Ti adhesion layer on the overall response of Au-based nano-scale SRRs. The results quantify the extent to which the overall difference in the resonance frequencies between Au- and Al-based SRRs is due to the presence of the Ti. We show that even a 2-nm-thick Ti layer can red-shift the position of SRR resonance by 20 nm. Finally, we demonstrate that by intentional addition of titanium in the Au-based SRRs, their overall resonant response can be tuned widely in frequency, but at the expense of resonance magnitude.

• Monolithic 45-GHz mode locked surface-etched DBR laser using quantum well intermixing technology

  L. Hou, M. Haji, R. Dylewicz, J. M. Arnold, A. C. Bryce

  15th European Conference on Integrated Optics (ECIO), Cambridge, United Kingdom; 01/2010

  45-GHz passively mode locked AlGaInAs/InP 1.55 μm lasers integrated with surface-etched distributed Bragg mirrors have been fabricated. Quantum well intermixing was used to provide low absorption loss gratings with accurate wavelength control. The lasers produce 3.6-ps Gaussian-pulses with TBP of 0.... [more] 45-GHz passively mode locked AlGaInAs/InP 1.55 μm lasers integrated with surface-etched distributed Bragg mirrors have been fabricated. Quantum well intermixing was used to provide low absorption loss gratings with accurate wavelength control. The lasers produce 3.6-ps Gaussian-pulses with TBP of 0.57.

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• Electron beam lithography of bulk zinc oxide wafers using a polythiophene-based charge dissipation layer

  R. Dylewicz, S. Lis, R. M. De La Rue, F. Rahman

  15th European Conference on Integrated Optics (ECIO), Cambridge, United Kingdom; 01/2010

  The ability of thin conductive polythiophene layers to dissipate electrons in electron-beam lithography process on ZnO is presented for the first time. Quick and inexpensive processing method is shown for an electron-beam lithography (EBL) exposure of dense and high-resolution patterns in hydrogen s... [more] The ability of thin conductive polythiophene layers to dissipate electrons in electron-beam lithography process on ZnO is presented for the first time. Quick and inexpensive processing method is shown for an electron-beam lithography (EBL) exposure of dense and high-resolution patterns in hydrogen silsesquioxane (HSQ) negative-tone resist deposited on bulk ZnO sample.

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• Monolithic 40 GHz passively mode-locked AlGaInAs/InP 1.55 μm MQW laser with surface-etched distributed Bragg reflector

  L. Hou, R. Dylewicz, M. Haji, P. Stolarz, B. Qiu, A. C. Bryce

  IEEE Photonics Technology Letters. 01/2010; 22:1503 - 1505.

  We have fabricated 40 GHz passively mode-locked AlGaInAs/InP 1.55 μm lasers integrated with surface-etched distributed Bragg mirrors. Numerically optimized gratings provide low-scattering losses and accurate wavelength control. The lasers produce 4.46-ps Gaussian-pulses with TBP of 0.47.... [more] We have fabricated 40 GHz passively mode-locked AlGaInAs/InP 1.55 μm lasers integrated with surface-etched distributed Bragg mirrors. Numerically optimized gratings provide low-scattering losses and accurate wavelength control. The lasers produce 4.46-ps Gaussian-pulses with TBP of 0.47.

• Fabrication of submicron-sized features in InP/InGaAsP/AlGaInAs quantum well heterostructures by optimized inductively coupled plasma etching with Cl2/Ar/N2 chemistry

  R. Dylewicz, R. M. De La Rue, R. Wasielewski, P. Mazur, G. Mezősi, A. C. Bryce

  Journal of Vacuum Science and Technology B. 01/2010; 28:882-890.

  Inductively coupled plasma dry etching for the fabrication of fine-pitch patterns in a wide range of InP-based materials has been developed. The effect of plasma chemistry (the N2 content in the total Cl2/Ar/N2 gas mixture) on the degree of undercut in the sidewall profile and surface morphology has... [more] Inductively coupled plasma dry etching for the fabrication of fine-pitch patterns in a wide range of InP-based materials has been developed. The effect of plasma chemistry (the N2 content in the total Cl2/Ar/N2 gas mixture) on the degree of undercut in the sidewall profile and surface morphology has been studied. Optimization of the etch process conditions produces strong passivation effects on the sidewalls, together with a highly anisotropic process - while still maintaining a good etch rate (560 - 730 nm/min). Single-step etching using hydrogen silsesquioxane (HSQ) as a resist/hard-mask resulted in high aspect ratio features being obtained (up to 30:1). Low plasma excitation power (ICP machine operating power of 400 W) and moderate ion energy (RF power = 120 W) were utilized to minimize etch-induced damage and provide low scattering losses. Low-loss (< 0.3 dB/mm) optical ridge waveguides and high reflectivity and high-wavelength selectivity (delta_lambda = 2 nm) results of 236 nm-period sidewall gratings were demonstrated experimentally.