J. A. Gupta

National Research Council Canada, Ottawa, Ontario, Canada

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Publications (140)235.34 Total impact

  • Source
    E. Dupont, J. A. Gupta, H. C. Liu
  • Source
    E. Dupont, J. A. Gupta, H. C. Liu
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    ABSTRACT: We investigate two- and three-electron spin blockade in three vertical quantum dots (QDs) coupled in series. Two-electron spin blockade is found in a region where sequential tunneling through all QDs is forbidden but tunneling involving virtual hopping through an empty QD is allowed. It is observed only for the hole cycle with a distinct bias threshold for access to the triplet state. Three-electron spin blockade involving the quadruplet state is observed for nonequibilium conditions where sequential tunneling is allowed and the triplet state is accessible. Our results shine light on the importance of the nonequibilium conditions to obtain sufficient population of triplet and quadruplet states necessary for spin blockade.
    Physical Review Letters 01/2013; 110(1):016803. DOI:10.1103/PhysRevLett.110.016803 · 7.73 Impact Factor
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    ABSTRACT: Time resolved photoluminescence (PL) spectroscopy has been applied to study dynamics of localized excitons in a single Ga0.7In0.3N0.015As0.985/GaAs quantum well (QW). The decay time constant, τPL, has been determined for different PL peak energies at various temperatures. An increase in temperature produced two effects: (i) a reduction of τPL and (ii) changes in the τPL dispersion. These two experimental observations as well as the shape of PL decay curves were very well reproduced by Monte-Carlo simulations of hopping excitons with parameters derived from PL and photoreflectance measurements for this QW.
    Applied Physics Letters 05/2012; 100(20). DOI:10.1063/1.4714739 · 3.52 Impact Factor
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    ABSTRACT: Time-resolved photoluminescence (PL) characteristics of type-II GaAsSb/GaAs quantum wells are presented. The PL kinetics are determined by the dynamic band bending effect and the distribution of localized centers below the quantum well band gap. The dynamic band bending results from the spatially separated electron and hole distribution functions evolving in time. It strongly depends on the optical pump power density and causes temporal renormalization of the quantum well ground-state energy occurring a few nanoseconds after the optical pulse excitation. Moreover, it alters the optical transition oscillator strength. The measured PL lifetime is 4.5 ns. We point out the critical role of the charge transfer processes between the quantum well and localized centers, which accelerate the quantum well photoluminescence decay at low temperature. However, at elevated temperatures the thermally activated back transfer process slows down the quantum well photoluminescence kinetics. A three-level rate equation model is proposed to explain these observations.
    Journal of Physics Condensed Matter 04/2012; 24(18):185801. DOI:10.1088/0953-8984/24/18/185801 · 2.22 Impact Factor
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    ABSTRACT: A lateral etched-grating process was used to produce singlemode distributed feedback laser diodes at 3.23 μm. The devices are based on InGaAsSb/AlInGaAsSb type-I quantum well active regions grown on GaSb substrates by molecular beam epitaxy. The lasers were used in high-resolution spectroscopy of methane gas near the v3, R7 vibrational absorption transitions.
    Electronics Letters 03/2012; 48(7):396-397. DOI:10.1049/el.2012.0109 · 1.07 Impact Factor
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    ABSTRACT: We present the electronic properties of a triple quantum dot molecule embedded inside a sub-micron mesa, made from a quadruple-barrier triple-quantum-well structure, and surrounded by a single gate electrode. We outline the design principles of the quadruple-barrier triple-quantum-well structure and calculate the energy of the three lowest states as a function of center well thickness. We observe regular and irregular shaped Coulomb diamond regions similar to those for double quantum dot devices. Variation in the Coulomb blockade region shape is introduced by fluctuation in the offset energies between the quantum dots likely associated with device processing and random impurity potential in the material. We also present Coulomb blockade patterns calculated with a constant interaction model for sequential tunneling through the three series-coupled quantum dots.
    Japanese Journal of Applied Physics 02/2012; 51(2). DOI:10.1143/JJAP.51.02BJ06 · 1.06 Impact Factor
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    ABSTRACT: The HF gas detection sensitivity of GaSb-based distributed feedback lasers was studied in order to evaluate the potential use of operating temperature to control the laser output power in field applications. Measurements were made in the 2f wavelength modulation spectroscopy mode to monitor a prominent HF absorption feature at 2396 nm. An Allan variance analysis indicates that the best sensitivity is obtained when a larger thermoelectric current is applied to maintain temperature control by actively heating or cooling the laser. The reduced detection sensitivity for a setpoint near the ambient laser operating temperature is similar to that obtained without active temperature control.
    Electronics Letters 01/2012; 48(2):114-116. DOI:10.1049/el.2011.3369 · 1.07 Impact Factor
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    ABSTRACT: Narrow ridge waveguide (5um) laser diodes were fabricated using type-I InGaAsSb/AlInGaAsSb quantum well active regions on GaSb. The devices operate in continuous-wave mode near 3254nm with a total light output of 7.4mW at 20°C (uncoated facets).
    Lasers and Electro-Optics (CLEO), 2012 Conference on; 01/2012
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    ABSTRACT: We characterize and model the single-particle energy level position and resonant current strength at a three-level crossing in a coherent mixer composed of two weakly coupled vertical quantum dots. In addition to clear anticrossing behavior, an otherwise strong resonance is completely extinguished at the center of the crossing. Despite the strong variation in energy level position and resonant current strength throughout the crossing region, the resonance widths and the sum of the branch currents are found to be approximately constant.
    12/2011; DOI:10.1063/1.3666692
  • D. G. Austing, C. Payette, G. Yu, J. A. Gupta
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    ABSTRACT: We outline the properties of fine structure in the high bias (~10-100 mV) current of a weakly coupled vertical double-dot device close to ``pinch-off''. Two features of particular interest at 0 T are modulations in the strength along the length of the practically degenerate 1s-2p+ and 1s-2p- resonance lines, and a current step bisecting these two resonance lines whose height is very different either side of the two resonance lines.
    12/2011; DOI:10.1063/1.3666364
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    ABSTRACT: Efficient femtosecond mode locking is reported in the 1985-2065 nm range for a Tm:KYW laser. Transform-limited 386-fs pulses at 2030nm are produced at a pulse repetition frequency of 97.4MHz and average output power of 235mW.
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    ABSTRACT: Efficient mode-locking in a Tm:KY(WO(4))(2) laser is demonstrated by using InGaAsSb quantum-well SESAMs. Self-starting ultrashort pulse generation was realized in the 1979-2074 nm spectral region. Maximum average output power up to 411 mW was produced around 1986 nm with the corresponding pulse duration and repetition rate of 549 fs and 105 MHz respectively. Optimised pulse durations of 386 fs were produced with an average power of 235 mW at 2029 nm.
    Optics Express 05/2011; 19(10):9995-10000. DOI:10.1364/OE.19.009995 · 3.53 Impact Factor
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    ABSTRACT: Detection sensitivity of <20 ppb-cm of HF gas is achieved with CW GaSb-based DFB lasers at 2396 nm. Sensitivity was characterized over laser operating temperature and output power.
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    ABSTRACT: Reported for the first time is a full GaAs-based room-temperature near infrared (NIR) up-conversion device fabricated by wafer-fusing a GaNAsSb/GaAs pin photodetector (PD) with a GaAs/AlGaAs light emitting diode (LED). NIR photons with wavelengths in the range 1.3-1.6 μm were up-converted to 0.87 μm.
    Electronics Letters 04/2011; 47(6-47):393 - 395. DOI:10.1049/el.2010.3543 · 1.07 Impact Factor
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    ABSTRACT: We investigate Pauli spin blockade and the influence of hyperfine interaction for a system of six-electrons in a device composed of two weakly coupled vertical quantum dots. As a consequence of a large built-in offset energy between the dots, the relevant charge configurations consist of one (zero) and five (six) electrons on the upstream dot and downstream dot respectively. On sweeping the out-of-dot-plane magnetic field up and down, abrupt steps and hysteresis in the leakage current are observed in the Pauli spin blockade region that evolve systematically with bias. We propose a model to explain our observations in terms of hyperfine induced singlet--triplet mixing.
    Journal of the Physical Society of Japan 02/2011; 80(2). DOI:10.1143/JPSJ.80.023701 · 1.48 Impact Factor
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    ABSTRACT: The carrier dynamics in type-II GaAsSb/GaAs quantum well (QW) is investigated by time-resolved photoluminescence at low temperature. A detailed analysis of the experimental data reveal a complex carrier relaxation scenario involving both delocalized and localized states. We show that the QW emission is controlled by the dynamics of the band bending effect, related to temporal changes in the spatial charge separation near the GaAsSb/GaAs heterointerface, whereas localized states play a significant role in the carrier relaxation/redistribution between QW states.
    Applied Physics Letters 02/2011; 98(6):061910-061910-3. DOI:10.1063/1.3548544 · 3.52 Impact Factor
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    ABSTRACT: Type-I interband laser diodes were developed for trace gas sensing applications in the 2-4um wavelength range. The devices were grown by molecular beam epitaxy on GaSb substrates using InGaAsSb/Al(In)GaAsSb active regions. Tunable, single-mode lasers were produced using distributed feedback grating processing or by incorporating Fabry-Perot lasers in an external cavity configuration. Sensitive gas detection was demonstrated using these lasers in tunable-diode laser absorption spectroscopy. I. INTRODUCTION There are many applications for gas sensing systems based on mid-infrared laser diodes. Trace gas sensing with a single- mode laser can be accomplished using tunable diode laser absorption spectroscopy (TDLAS), in which the wavelength of the laser is modulated through a strong absorption feature of the gas of interest, in a wavelength range free of interferences from other species. Laser diodes in the 2-3um range can be readily produced on GaSb substrates using compressively- strained InGaAsSb type-I quantum wells surrounded by AlGaAsSb waveguide and cladding layers which are lattice- matched to the substrate. Molecular beam epitaxy (MBE) is a preferred technique for the growth of these structures because of its excellent thickness and compositional control. These properties are even more important for the development of devices with wavelengths beyond 3um. In this case, it has been demonstrated that laser performance can be improved through the use of quinary AlInGaAsSb barrier layers, which simultaneously increase the hole confinement and decrease the conduction band offset (1). This more favourable band offset prevents hole leakage and improves the homogeneity of electron injection into multiple quantum well active regions. In this work we have developed single-mode lasers using quantum well active regions designed for specific operating wavelengths of 2476nm and 3240m. The shorter wavelength, single-mode devices were fabricated using a regrowth-free distributed feedback (DFB) process(2) involving laterally- coupled etched gratings to provide continuous single-mode tuning with current and temperature through absorption features of HF gas. Single-mode operation at longer wavelengths was achieved by controlled adjustment of a diffraction grating in an external cavity configuration. The resulting single-mode lasers operate at wavelengths around 3240nm, which is extremely important for the detection of methane and other hydrocarbons. II. EXPERIMENT The laser structures were grown on (100) GaSb:Te substrates in a V90 MBE system using conventional group-III effusion cells and valved cracker cells for As2 and Sb2. The structures consist of Te- and Be-doped Al0.6Ga0.4As0.052Sb0.948 cladding layers lattice-matched to the GaSb substrate (thicknesses in the range 1.5-3.0um). The composition and thickness of the quantum-well active region for each laser was carefully designed for the intended application. For the laser structure with target wavelength of 2476nm, the active region contains three 10.9nm In0.43Ga0.57As0.15Sb0.86 quantum wells separated by 30nm, with Al0.24Ga0.76As0.02Sb0.98 barrier and waveguide layers. Single-mode DFBs at 2476nm were produced using a two step inductively-coupled plasma reactive ion etching (ICP-RIE) procedure. In the first step, a narrow ridge waveguide structure was etched in the semiconductor. In the second step, first- order lateral gratings were etched on either side of the ridge to provide evanescent coupling to the optical mode (grating pitch λ=349.12nm, 50% duty cycle, thickness 330nm). E-beam lithography with fine-pitch control was used to write the lateral gratings using ZEP resist. Standard TiPtAu and NiGeAu metallization was used for the p- and n-contacts, respectively. After cleaving, the front output facet of the lasers was coated with a single layer of Al2O3 using ion-beam sputter deposition to provide a reflectivity of approximately 7%. The back facet of the laser was coated with a similar Al2O3 layer, followed by a multilayer stack of SiO2/TiO2 to provide a reflectivity of 90%. With these coatings, approximately 97% of the laser light should be emitted from the front facet.
  • MRS Online Proceeding Library 01/2011; DOI:10.1557/PROC-829-B11.5
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    ABSTRACT: We report on the spectroscopic characterization, continuous-wave and continuous wave mode-locked laser performance of bulk Tm(3+):GPNG fluorogermanate and Tm(3+)-Ho(3+):TZN tellurite glass lasers around 2 μm. A slope efficiency of up to 50% and 190 mW of output power were achieved from the Tm(3+):GPNG laser at 1944 nm during continuous wave operation. The Tm(3+)-Ho(3+):TZN laser produced a 26% slope efficiency with a maximum output power of 74 mW at 2012 nm. The Tm(3+):GPNG produced near-transform-limited pulses of 410 fs duration centered at 1997 nm with up to 84 mW of average output power and repetition frequency of 222 MHz when was passively modelocked using an ion-implanted InGaAsSb-based quantum well SESAM. Using the same SESAM, the Tm(3+)-Ho(3+):TZN laser generated 630-fs pulses with 38 mW of average output power at 2012 nm. Data analysis of pulses at different intracavity pulse energies provided an estimation of n(2) at 2012 nm of 2.9 × 10(-15) cm(2)/W for the Tm(3+)-Ho(3+):TZN.
    Optics Express 10/2010; 18(21):22090-8. DOI:10.1364/OE.18.022090 · 3.53 Impact Factor

Publication Stats

995 Citations
235.34 Total Impact Points


  • 2001–2013
    • National Research Council Canada
      • Institute for Microstructural Sciences (IMS)
      Ottawa, Ontario, Canada
  • 2011
    • Shanghai Jiao Tong University
      • Department of Physics
      Shanghai, Shanghai Shi, China
  • 2010
    • University of St Andrews
      • School of Physics and Astronomy
      Saint Andrews, SCT, United Kingdom
  • 2009
    • Tyndall National Institute
      Corcaigh, Munster, Ireland
  • 2006
    • Wroclaw University of Technology
      • Institute of Physics
      Vrotslav, Lower Silesian Voivodeship, Poland
    • Cardiff University
      Cardiff, Wales, United Kingdom
  • 2005
    • University of Ottawa
      Ottawa, Ontario, Canada
  • 2002
    • University of Toronto
      • Department of Materials Science and Engineering
      Toronto, Ontario, Canada
  • 1998–2000
    • Simon Fraser University
      • Department of Physics
      Burnaby, British Columbia, Canada