M. Pessa

Tampere University of Technology, Tammerfors, Province of Western Finland, Finland

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Publications (530)797.12 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: It was recently found that oxygen induces ordered reconstructions on several III–V surfaces. The most oxygen-rich reconstruction shows (3 × 1) periodicity. Based on first-principles investigations, a detailed atomic model is presented for this reconstruction. The uncommon periodicity is attributed to the highly stable InOIn trilayer below surface which also leads to stabilizing additional bonds within the surface layer. The strain induced by the trilayer is more effectively accommodated within the (3 × 1) reconstruction than within the competing (2 × 1) reconstruction due to smaller number of dimers. It is proposed that the experimentally found semiconductivity is reached by substitutional atoms within the surface layer. Suitable substitution preserves the magnitude of the bulk band gap.
    No preview · Article · Dec 2012 · Surface Science
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    ABSTRACT: The influence of non-radiative recombination on the photoluminescence decay time (τPL) has been studied for GaInNAs/GaAs quantum wells with Ga- and In-rich environments of N atoms. At low temperatures, this influence is suppressed, due to the carrier localization phenomenon, which leads to a spectral dispersion of τPL. For investigated samples, this dispersion has been found to be in the range of ~0.2–2.0 ns. With the temperature increase, the free exciton emission starts to dominate instead of the localized exciton emission and the dispersion of τPL disappears. The dynamic of free exciton recombination is strongly influenced by the non-radiative recombination, which varies between samples, due to different concentration of non-radiative centers. The study of influence of non-radiative recombination on τPL has been performed at 180 K, since this temperature is high enough to eliminate the localized emission and activate non-radiative recombination and low enough to observe excitonic emission without strong contribution of free carrier recombination when the sample is excited with low power. It was observed that, for as-grown samples, the τPL increases from 0.14 to 0.25 ns with the change in As/III beam equivalent pressure ratio from 3.8 to 12.1 (in this case, it corresponds to the change in nitrogen nearest-neighbor environment from Ga- to In-rich), whereas, after annealing (i.e., also the change from Ga-rich to In-rich environment of N atoms), this time increases 2–4 times, depending on the As/III ratio. It has been concluded that the τPL is influenced by point defects rather than the nitrogen nearest-neighbor environment, but their concentration is correlated with the type of nitrogen environment.
    No preview · Article · Mar 2012 · Journal of Applied Physics
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    ABSTRACT: Highly polarized light from an InGaN/GaN light emitting diode is proposed using an embedded multi-layer metallic/dielectric sub-wavelength grating and a dielectric transition layer. Transmission of transverse magnetic mode (TTM), reflection of transverse electric mode, and polarization extinction ratio (ER) were calculated using commercial “GSOLVER” software, based on a full vector implementation of Rigorous Coupled-Wave Analysis algorithm. TTM and ER were found to be largely enhanced by the presence of the transition layer, made of MgF2 or SiO2, placed between GaN and the grating section. TTM>95% and ER>34dB for closely optimized Al/MgF2 gratings were predicted. These values are significantly higher than those obtained by single-layer metallic gratings.
    No preview · Article · Oct 2011 · Thin Solid Films
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    ABSTRACT: Amorphous surface oxides of III–V semiconductors are harmful in many contexts of device development. Using low-energy electron diffraction and photoelectron spectroscopy, we demonstrate that surface oxides formed at Sn-capped GaAs(100) and InAs(100) surfaces in air are effectively removed by heating. This Sn-mediated oxide desorption procedure results in the initial well-defined Sn-stabilized (1×2) surface even for samples exposed to air for a prolonged time. Based on ab initio calculations we propose that the phenomenon is due to indirect and direct effects of Sn. The Sn-induced surface composition weakens oxygen adsorption.
    Full-text · Article · Jun 2011 · Applied Physics Letters
  • C. Tan · Tapio Niemi · Changsi Peng · Markus Pessa
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    ABSTRACT: We present a new graded-index photonic crystal (GRIN PhC) structure which can be made by laser interference lithography (LIL). It can be applied as miniaturized focusing lens. Numerical simulations are carried out on the structures with different widths, lengths, and modulations. In the qualitative analysis of the focal length, focusing of a GRIN PhC was proved to originate from both the graded sizes of the rods and multimode interference. Multimode interference dominates the focusing effect when a GRIN PhC has a small length or a small difference in the rod sizes. Intensity distributions in different cases were given to support the conclusion.
    No preview · Article · Jun 2011 · Optics Communications
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    ABSTRACT: Previously found oxidized III-V semiconductor surfaces have been generally structurally disordered and useless for applications. We disclose a family of well-ordered oxidized InAs, InGaAs, InP, and InSb surfaces found by experiments. The found epitaxial oxide-III-V interface is insulating and free of defects related to the harmful Fermi-level pinning, which opens up new possibilities to develop long-sought III-V metal-oxide-semiconductor transistors. Calculations reveal that the early stages in the oxidation process include only O-III bonds due to the geometry of the III-V(100)c(8×2) substrate, which is responsible for the formation of the ordered interface. The found surfaces provide a different platform to study the oxidation and properties of oxides, e.g., the origins of the photoemission shifts and electronic structures, using surface science methods.
    No preview · Article · May 2011 · Physical review. B, Condensed matter
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    ABSTRACT: We report a comparative study on selective epitaxy of nanostructures with different geometrical shapes. GaAs pyramids were grown by molecular beam epitaxy into circular holes, L-shaped holes, and cross-shaped holes, patterned using nanoimprint lithography. These GaAs nanostructures were used for guided-self assembly of InAs QDs. The results show that the initial shapes of the nanostructures have a strong effect on the nucleation of InAs QDs. Cross-shaped holes were found to be the most resilient against form changes when the height of the pyramid was increased. On the other hand the L-shaped islands became unusable for QD growths when more than twenty nanometers of GaAs was grown onto the patterns. Photoluminescence measurements on QDs embedded within the GaAs islands showed that the peak emission wavelength was similar for all types of pyramids.
    No preview · Article · May 2011 · Journal of Crystal Growth
  • M. Pessa · J. Lilja · O. Jylhä · M. Ishiko · H. Asonen
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    ABSTRACT: At the time being, there is evidently a sharp increase of interest in growth of low-dimensional thin-film structures of semiconducting compounds by the Atomic Layer Epitaxy (ALE) method. Many of the wide-gap II-VI compounds can be grown from elemental source materials by an ALE mode related to Molecular Beam Epitaxy (MBE). This paper concentrates on recent ALE work involving ZnSe- and CdTe- derived diluted magnetic semiconductors (DMS) where a fraction of Zn or Cd is substituted by Mn atoms. It shows that Zn1-xMnxSe/ZnSe and Cd1-xMnxTe/CdTe DMS structures with abrupt interfaces and high structural perfection can be produced at low growth temperatures by the ALE method.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    ABSTRACT: The article is devoted to a promising technology for fabrication of two-dimensional nanoperiodic structures on solid surfaces by four-beam standing wave pulsed laser modification. In this method, a large number of spots (up to 107) less than 100 nm in size heated up to several thousand degrees are formed on the modified surface as a result of the interference of the four laser beams incident on the object coherently. Besides a direct laser ablation, various nonlinear mechanisms of surface modification may take place in the standing wave maxima. This way, a nearly perfect two-dimensional pattern can be formed on the modified surface; the pitches of the pattern in both directions can be adjusted easily within the range from a few microns to tens of nanometers by simply varying the beams' incidence angles. This method being developed extensively at present is very promising for application in microelectronics, data storage, integrated optics (including fabrication of the Bragg mirrors, antireflection coating, two-dimensional photonic crystals, etc.) and is considered to be a promising alternative to X-ray that the nanoperiodic pattern can be formed in a single step (actually, at single laser pulse) by direct laser ablation of the material. However, the method could be applied as well to patterning a resist deposited onto the processed substrate to serve as a lithographic mask. In this article, we present some experimental results on patterning various materials, such as metal films on semiconductor and glass substrates, polyimide, and even such a hard material as diamond by direct laser ablation using a XeCl excimer laser. Patterning a resist film, the phase masks on fused silica and the antireflection structures on Si and silica glass have been fabricated. Also, using the effect of stimulation of selfassembling of the semiconductor nanostructures by standing wave laser irradiation discovered by the authors, we have fabricated the ordered arrays of nanoislands on the surface of single crystal Si and GaAs and of GaAs/InxGa1-xAs/GaAs(001) heterostructures with the diameter ranging from 5 to 60 nm.
    No preview · Article · Jan 2011

  • No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    ABSTRACT: GaAs layers were grown on Si (001) substrates by molecular beam epitaxy (MBE) and migration enhanced epitaxy (MEE). They were examined by transmission electron microscopy, doublecrystal X-ray diffraction and Rutherford backscattering/channeling technique. Initial layer growth in both MEE and MBE was governed by three-dimensional nucleation but a stronger tendency for GaAs islands to align along the surface steps of Si was observed in the case of MEE. There was no measurable tilt between the (001) planes of GaAs and Si if growth was initiated by MEE at low temperature, prior to further growth by MBE at higher temperatures. On the contrary, the tilt angle was 0.34• when the entire structure was prepared by conventional two-step MBE. Rutherford backscattering measurements indicated a significant reduction in the density of defects throughout MEE/MBE GaAs in comparison with MBE GaAs.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    ABSTRACT: Optically pumped semiconductor disk lasers (OP-SDL) combine many advan- tages of traditional solid-state lasers with the versatility offered by the wide range of available semiconductor gain materials. SDLs provide a good quality, nearly diffraction limited, Gaussian shaped beam and the external cavity enables the use of intra-cavity filters for achieving narrow linewidth and wavelength tunability. GaSb-based com- pound semiconductors can be tailored to cover a broad spectral range, extending from 2 μm to beyond 3 μm. They are the prime choice for the development of lasers to be used in spectroscopy of atmospheric gasses, laser surgery, remote sensing, or military countermeasures.(1, 2) In this study we demonstrate a high power continuous wave SDL emitting at 2 μm. The structure consists of 18.5 pairs of GaSb/AlAsSb distributed Bragg reflector and a gain region with 15 InGaSb quantum-wells (QWs) embedded in GaSb. A 2.5×2.5 mm2-size gain chip was capillary bonded with water to a type IIa natural dia- mond heat spreader to enable efficient heat removal from the active region. The bonded chip was finally pressed between two copper plates, with a small hole in the top plate allowing the passage of pump and signal. The mounted sample was attached to a water cooled copper heat sink. The laser cavity had a V-type configuration consisting of the mounted gain chip, a high reflective folding mirror with radius of curvature of 200 mm, and a 2 % transmis- sive planar output coupler. A 980 nm diode laser was used for optical pumping of the gain region and the pump beam was focused to a spot of about 290 μm in diameter at an angle of 22° to the surface normal. The highest output powers, over 4 W, were achieved near room temperatures and lasing with over 1-W power was observed still at 50 °C. The laser could be tuned about 75 nm using a birefringent filter inside the cavity. Wider tuning range was dem- onstrated - more than 150 nm - by utilizing QWs with different thickness in the active region. In addition, short-pulse generation exploiting GaSb-SESAMs for passive mode- locking is presented.
    Full-text · Article · Jan 2011
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    ABSTRACT: The paper presents the modelling and design particularities of laterally-coupled distributed feedback lasers (LC-DFB), the fabrication process, involving a highly productive and cost-effective UV-nanoimprint lithography technique, and the characteristics obtained up to now for the LC-DFB lasers fabricated for pumping Cesium atomic clocks. 550 μm long LC-DFB lasers, emitting at 894 μm, had 10 mA threshold currents and maintained over 40dB side-mode-suppression-ratio between 10 and 100°C. The measured self-homodyne spectrum indicated a linewidth below 1.3 MHz for AR/HR-coated 1000 μm long LC-DFB lasers and the simulations indicate that the use of phase-shift sections could reduce the linewidth below 250 kHz.
    No preview · Conference Paper · Nov 2010
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    ABSTRACT: The effect of in‐situ N‐ion irradiation on the recombination dynamics of GaInNAs∕GaAs semiconductor saturable absorber mirrors has been studied. The samples were fabricated by molecular beam epitaxy using a radio frequency plasma source for nitrogen incorporation in the absorber layers as well as for the irradiation. The recombination dynamics of irradiated samples were studied by pump‐probe measurements. The recombination time of the absorbers could be reduced by increasing the irradiation time. The effect of the reduced recombination time on the pulse dynamics of a mode‐locked laser setup was studied with a Bi‐doped fibre laser. The pulse quality was found to improve with increased irradiation time and reduced recombination time, demonstrating the potential of the in‐situ irradiation method for device applications.
    No preview · Article · Nov 2010
  • Juha M. Kontio · Janne Simonen · Juha Tommila · Markus Pessa
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    ABSTRACT: We introduce a novel method for fabricating nanocones of various metals. Based on a combination of UV-nanoimprint lithography and electron beam evaporation, the method enables fast, high volume, and reproducible fabrication of conical nanostructures on flat substrates. We investigate cone formation with eight different metals and find that the shape of the cone depends on the material characteristics of the deposited metal.
    No preview · Article · Nov 2010 · Microelectronic Engineering
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    ABSTRACT: Self-assembled InAs quantum dots (QDs) have been incorporated into GaAs Schottky diodes. We intentionally introduce defects by growing the QDs above the critical thickness for plastic relaxation. The strain-relaxed QDs introduce electrically active defects in n- as well as p-type diodes. We identify dislocation induced defects and point defects, and can show that in n-type GaAs the EL6 defect plays a major role in the relaxation of QDs. Furthermore, we compare the introduction of defects in strain relaxed QDs grown by looped and non-looped deposition and depending on an in-situ annealing step. We observe that looped deposited QDs exhibit a better quality compared to non-looped QDs even if they are grown beyond the critical thickness for plastic relaxation. An introduction of an annealing step after the growth of the QDs completely removes the defects in both QD system.
    No preview · Article · Sep 2010 · Physica E Low-dimensional Systems and Nanostructures
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    ABSTRACT: Contactless electroreflectance (CER) has been applied to study band bending in Be-doped GaInNAs/GaAs quantum wells (QWs). It has been shown that (i) the sign of GaAs-related CER signal changes from positive to negative due to Be-doping and (ii) QW-related CER resonances disappear for Be-doped QWs whereas they are clearly observed for un-doped QWs. The two observations indicate a Be-related shift in the Fermi level above the hole levels in the QW region, i.e., the change in band bending in this system. The results point out that the experimentally-observed enhancement in QW photoluminescence upon Be-doping is associated with a better collection/confinement of photogenerated carriers by the Be-doped GaInNAs QW. (C) 2010 American Institute of Physics. [doi:10.1063/1.3462299]
    Full-text · Article · Jul 2010 · Applied Physics Letters
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    ABSTRACT: Technologically useful indium- (In) terminated c(8×2)-reconstructed GaAs(100) substrate surface has been studied by first-principles calculations and scanning tunneling microscopy (STM) measurements. Our total-energy calculations demonstrate the stability of four different so-called ζa structures with In monomer rows and In coverage between 0.5 and 2 monolayers on the GaAs(100) substrate. Thus, we introduce a surface system, which stabilizes the ζa reconstruction. Furthermore, an interesting trend is found. Atomic structure of the c(8×2) reconstruction depends on the surface-layer cation and substrate volumes, which, in principle, allows to tune the surface structure by cation adsorption. This phenomenon is related to the peculiar c(8×2) atomic surface structure, which shows mixed surface layer, including both anions and cations, and uncommon metallic-type cations in the ζa structure, which do not show covalent bonds. Our results predict a structural transition from the ζ structure to the ζa structure as the surface cation size is increased at 0 K. The found transition is probably related to the disordered surface structures (consisting of ζ and ζa building blocks) found experimentally by x-ray diffraction at room temperature. Comparison of the STM images, calculated for various c(8×2) models, with the former and present measured STM images of In/GaAs(100)c(8×2) supports the presence of stable ζa reconstructions.
    No preview · Article · Jun 2010 · Physical review. B, Condensed matter
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    ABSTRACT: Nanoperforated membranes can transmit light and modify either the spectral or the spatial properties of the beam passing through the membrane. Alternatively, the perforated membrane can be used as a precisely fabricated filter for nanoparticles, fluids or gases. We made membranes made on a silicon nitride layer deposited on silicon wafer with nanopatterning was realized by nanoimprint lithography. We present two components based on these nanopatterned membranes. Firstly, we demonstrate large-area nanoperforated membranes. The perforations through a 1500nm thick free-standing silicon nitride (SiN) film have a diameter of 350nm and a period of 700nm. The area of the largest free-standing films was 25mm2. Secondly, we demonstrate small area membranous optical elements and a method to couple them to optical fibers. Our component uses an optical element processed on the SiN-membrane on silicon wafer. Light is launched and collected through the fiber glued in the trough-wafer via. This component demonstrates a novel and simple way to couple mass producible optical elements with optical fibers. Finally, we fabricate an optical filter utilizing guided-mode resonance on the SiN-membrane. The filter utilizes fiber coupling, and we demonstrate its use as a refractive index sensor.
    No preview · Article · May 2010 · Microelectronic Engineering
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    ABSTRACT: Four-beam laser interference is shown to stimulate the self-organisation of periodic two-dimensional arrays of nanoislands on the surface of GaAs/InGaAs/GaAs epitaxial structures. (Self-organisation is here taken to mean processes that determine the island size.) The island size distribution has two well-defined maxima. The smaller islands (~5 nm) form inside each heat-affected zone, and the larger islands (~15 nm), at the periphery of such zones. The island width is a factor of 20 — 60 smaller than the standing wave period, which can be accounted for in terms of the elastic stress on the surface of the epitaxial film.
    No preview · Article · Mar 2010 · Quantum Electronics

Publication Stats

5k Citations
797.12 Total Impact Points


  • 1978-2012
    • Tampere University of Technology
      • • Optoelectronics Research Centre
      • • Department of Physics
      • • Department of Electrical Engineering
      Tammerfors, Province of Western Finland, Finland
  • 2002-2008
    • University of Strathclyde
      • Institute of Photonics
      Glasgow, SCT, United Kingdom
    • University of Helsinki
      • Laboratory of Physical Chemistry
      Helsinki, Uusimaa, Finland
  • 2007
    • University of Bristol
      • Department of Electrical and Electronic Engineering
      Bristol, England, United Kingdom
    • University of Pavia
      Ticinum, Lombardy, Italy
  • 1998-2002
    • University of Tampere
      Tammerfors, Pirkanmaa, Finland
    • Johannes Kepler University Linz
      • Institut für Experimentalphysik
      Linz, Upper Austria, Austria
  • 2000
    • Northeastern University
      • Department of Physics
      Boston, MA, United States
  • 1996
    • University of Tartu
      Dorpat, Tartu, Estonia
  • 1976
    • University Hospital München
      München, Bavaria, Germany