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  • 1. Akram, Muhammad Nadeem
    et al.
    Xiang, Yu
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Yu, Xingang
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Zabel, Thomas
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Hammar, Mattias
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Influence of base-region thickness on the performance of Pnp transistor-VCSEL2014In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 22, no 22, p. 27398-27414Article in journal (Refereed)
    Abstract [en]

    We have recently reported a 980nm GaAs-based three terminal Pnp transistor-vertical-cavity surface-emitting laser (TVCSEL) operating at room temperature with optical power up to 1.8mW. However, the current gain beta = Delta I-c/Delta I-b was near zero just before lasing and became negative after the lasing threshold. The main cause of the negative current gain was found to be a gradual and position-dependent forward-biasing (saturation) of the base-collector junction with increasing bias even before lasing threshold. In this article, detailed multi-physics device simulations are performed to better understand the device physics, and find ways to avoid the premature saturation of the base-collector junction. We have optimized the thickness of the base region as well as its doping concentration and the location of the quantum wells to ensure that the T-VCSEL is in the active mode throughout its range of operation. That is, the emitter-base junction is forward biased and base-collector junction is reversed biased for sweeping the excess charges out of the base region.

  • 2.
    Asadollahi, Ali
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Radamson, Henry
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Zabel, Thomas
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Hellström, Per-Erik
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Fabrication of strained Ge on insulator via room temperature wafer bonding2014In: 2014 15th International Conference on Ultimate Integration on Silicon, ULIS 2014, IEEE Computer Society, 2014, p. 81-84Conference paper (Refereed)
    Abstract [en]

    This work describes a strained germanium on insulator (GeOI) fabrication process using wafer bonding and etch-back techniques. The strained Ge layer is fabricated epitaxially using reduced pressure chemical vapor deposition (RPCVD). The strained Ge is grown pseudomorphic on top of a partially relaxed Si 0.66Ge0.34 layer. Wafer bonding is performed at room temperature without post-anneal processes and the etch-back steps are performed without mechanical grinding and chemical mechanical polishing (CMP).

  • 3.
    Asadollahi, Ali
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Zabel, Thomas
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Roupillard, Gabriel
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Radamson, Henry H.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Hellström, Per-Erik
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Fabrication of relaxed germanium on insulator via room temperature wafer bonding2014In: ECS Transactions: Volume 64, Cancun, Mexico, October 5 – 9, 2014 2014 ECS and SMEQ Joint International Meeting, Electrochemical Society, 2014, no 6, p. 533-541Conference paper (Refereed)
    Abstract [en]

    We report on the fabrication of, high quality, monocrystalline relaxed Germanium with ultra-low roughness on insulator (GeOI) using low-temperature direct wafer bonding. We observe that a two-step epitaxially grown germanium film fabricated on silicon by reduced pressure chemical vapor deposition can be directly bonded to a SiO2 layer using a thin Al2O3 as bonding mediator. After removing the donor substrate silicon the germanium layer exhibits a complete relaxation without degradation in crystalline quality and no stress in the film. . The results suggest that the fabricated high quality GeOI substrate is a suitable platform for high performance device applications.

  • 4.
    Gustafsson, Oscar
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Karim, Amir
    Asplund, Carl
    Wang, Qin
    Zabel, Thomas
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Almqvist, S.
    Savage, S.
    Andersson, Jan Y.
    Hammar, Mattias
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    A performance assessment of type-II interband In0.5Ga0.5Sb QD photodetectors2013In: Infrared physics & technology, ISSN 1350-4495, E-ISSN 1879-0275, Vol. 61, p. 319-324Article in journal (Refereed)
    Abstract [en]

    Self-assembled quantum-dot (QD) structures with type-II band alignment to the surrounding matrix material have been proposed as a III/V material approach to realize small-bandgap device structures suitable for photon detection and imaging in the long-wavelength infrared (LWIR) band. Here, we analyze the photoresponse of In0.5Ga0.5Sb/InAs QD photodiodes and estimate the system performance of type-II QD - based photodetectors. A review of alternative design approaches is presented and the choice of matrix material is discussed in terms of band alignment and its effect on the photoresponse. Photodiodes were fabricated consisting of 10 layers of In0.5Ga0.5Sb QDs grown on InAs (0 0 1) substrates with metal-organic vapor-phase epitaxy (MOVPE). The photoresponse and dark current were measured in single pixel devices as a function of temperature in the range 20-230 K. The quantum efficiency shows an Arrhenius type behavior, which is attributed to hole trapping. This severely limits the detector performance at typical LWIR sensor operating temperatures (60-120 K). A device design with the matrix material InAs0 6Sb0 4 is proposed as a mean to improve the performance by reducing the barrier for hole transport. This can potentially allow type-II InGaSb QDs to be a competitive sensor material for LWIR detection.

  • 5.
    Hammar, Mattias
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Xiang, Yu
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Yu, Xingang
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Berggren, Jesper
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Zabel, Thomas
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Akram, M. N.
    Room-temperature operation of 980-nm transistor-vertical-cavity surface-emitting lasers2013In: 2013 IEEE 6th International Conference on Advanced Infocomm Technology, ICAIT 2013, IEEE , 2013, p. 141-142Conference paper (Refereed)
    Abstract [en]

    We report on the design, fabrication and characterization of pnp-type 980-nm transistor-vertical-cavity surface-emitting lasers (T-VCSELs). Using an epitaxial regrowth process and a triple-intracavity current injection scheme we demonstrate static performance levels quite comparable to those of conventional VCSELs, including sub-mA threshold base current, mW-range output power and continuous-wave operation at least up to 50°C.

  • 6.
    Xiang, Yu
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Reuterskiöld-Hedlund, Carl
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Yu, Xingang
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Yang, Chen
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Zabel, Thomas
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Hammar, Mattias
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    AlGaAs/GaAs/InGaAs pnp-type vertical-cavity surface-emitting transistor-lasersManuscript (preprint) (Other academic)
    Abstract [en]

    We report on the design, fabrication and analysis of vertical-cavity surface-emitting transistor-lasers (T-VCSELs) based on the homogeneous integration of an InGaAs/GaAs VCSEL and an AlGaAs/GaAs pnp-heterojunction bipolar transistor (HBT). Epitaxial regrowth confinement, modulation doping, intracavity contacting and non-conducting mirrors are used to ensure a low-loss structure, and a variety of design variations are investigated for a proper internal biasing and current injection to ensure a wide operating range. Optimized devices show mW-range output power, mA-range base threshold current and high-temperature operation to at least 60°C with the transistor in its active mode of operation for base currents well beyond threshold. Current confinement schemes based on pnp-blocking layers or a buried tunnel junction are investigated as well as asymmetric current injection to improve the lateral feeding.

  • 7.
    Xiang, Yu
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Reuterskiöld-Hedlund, Carl
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Yu, Xingang
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Yang, Chen
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Zabel, Thomas
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Hammar, Mattias
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Akram, M. N.
    AlGaAs/GaAs/InGaAs pnp-type vertical-cavity surface-emitting transistor-lasers2015In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 23, no 12, p. 15680-15699Article in journal (Refereed)
    Abstract [en]

    We report on the design, fabrication and analysis of vertical-cavity surface-emitting transistor-lasers (T-VCSELs) based on the homogeneous integration of an InGaAs/GaAs VCSEL and an AlGaAs/GaAs pnp-heterojunction bipolar transistor (HBT). Epitaxial regrowth confinement, modulation doping, intracavity contacting and non-conducting mirrors are used to ensure a low-loss structure, and a variety of design variations are investigated for a proper internal biasing and current injection to ensure a wide operating range. Optimized devices show mW-range output power, mA-range base threshold current and high-temperature operation to at least 60 degrees C with the transistor in its active mode of operation for base currents well beyond threshold. Current confinement schemes based on pnp-blocking layers or a buried tunnel junction are investigated as well as asymmetric current injection for reduced extrinsic resistances.

  • 8.
    Xiang, Yu
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Reuterskiöld-Hedlund, Carl
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Yu, Xingang
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Yang, Chen
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Zabel, Thomas
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Hammar, Mattias
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Akram, Muhammed Nadeem
    University Collage of Buskerud and Vestfold.
    Performance Optimization of GaAs-Based Vertical-Cavity Surface-Emitting Transistor-Lasers2015In: IEEE Photonics Technology Letters, ISSN 1041-1135, E-ISSN 1941-0174, Vol. 27, no 7, p. 721-724Article in journal (Refereed)
    Abstract [en]

    We report on the optimization of pnp-type verticalcavity surface-emitting transistor-lasers based on the fusion between an AlGaAs/GaAs heterojunction bipolar transistor and an InGaAs/GaAs VCSEL using an epitaxial regrowth process. It is shown how a proper design of the base region can extend the transistor active range of operation well beyond lasing threshold, thereby resulting in typical transistor laser operational characteristics including mW-range output power, mA-range base threshold current, record-low power dissipation under laser operation, and continuous-wave operation up to at least 60°C. A pronounced breakdown in the collector current characteristics in the limit of high base current and/or emitter-collector voltage accompanied by a quenching of the optical output power is interpreted as being related to quantum well band-filling.

  • 9.
    Xiang, Yu
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Yu, Xingang
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Berggren, Jesper
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Zabel, Thomas
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Hammar, Mattias
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Akram, Muhammed Nadeem
    University Collage Vestfold.
    Minority current distribution in InGaAs/GaAs transistor-vertical-cavity surface-emitting laser2013In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 102, no 19, p. 191101-Article in journal (Refereed)
    Abstract [en]

    We compare experimental data with three-dimensional numerical calculations of the local minority current in an InGaAs/GaAs transistor vertical-cavity surface-emitting laser at different bias levels. It is demonstrated that lateral potential variations within the device greatly affect the transistor operating conditions. As a result, it locally operates in the active mode in the center of the device, allowing for efficient stimulated recombination, while it globally operates in the saturation regime as reflected by the measured current-voltage characteristics. This allows for excellent laser performance, including mW-range output power, sub-mA threshold base current, and continuous-wave operation well above room temperature.

  • 10.
    Yu, Xingang
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Xiang, Yu
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Berggren, Jesper
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Zabel, Thomas
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Hammar, Mattias
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Akram, Muhammad Nadeem
    Vestfold University Collage, Tönsberg, Norge.
    Shi, Wei
    University of British Columbia, Vancouver, Canada.
    Chrostowski, Lukas
    University of British Columbia, Vancouver, Canade.
    Room-temperature operation of transistor vertical-cavity surface-emitting laser2013In: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 49, no 3, p. 208-209Article in journal (Refereed)
    Abstract [en]

    The first room-temperature operation of a transistor vertical-cavity surface-emitting laser (T-VCSEL) is demonstrated. Fabricated using an epitaxial regrowth process, the T-VCSEL is electrically a pnp-type bipolar junction transistor and consists of an undoped AlGaAs/GaAs bottom DBR, an InGaAs triple-quantum-well active layer, an Si/SiO2 dielectric top DBR, and an intracavity contacting scheme with three electrical terminals. The output power is controlled by the base current in combination with the emitter-collector voltage, showing a voltage-controlled operation mode. A low threshold base-current of 0.8 mA and an output power of 1.8 mW have been obtained at room temperature. Continuous-wave operation was performed up to 50 degrees C.

  • 11.
    Yu, Xingang
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Xiang, Yu
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Zabel, Thomas
    Berggren, Jesper
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Hammar, Mattias
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    1.3 μm Buried Tunnel junction InGaAs/GaAs VCSELs2013Conference paper (Other academic)
    Abstract [en]

    Vertical cavity surface emitting lasers (VCSELs) working at 1.3μm are potential cost- and power-efficient sources for medium-range optical networks. However, they are still waiting for their commercial breakthrough due to several technological challenges related to the need for complex materials systems and/or fabrication methods. Nevertheless, many efforts have been devoted to solve the problem, also yielding some excellent results. Alter-native approaches we have previously presented are In-GaAs/GaAs 1.3-μm VCSELs based on oxidation con-finement or with an epitaxial regrowth of a pnp block-ing structure. Here we demonstrate a buried-tunnel junction (BTJ) current confinement scheme to improve the static and dynamic performance.

  • 12.
    Zabel, Thomas
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Reuterskiöld Hedlund, Carl
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Gustafsson, O.
    Karim, A.
    Berggren, Jesper
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Wang, Q.
    Ernerheim Jokumsen, Christopher
    KTH, School of Information and Communication Technology (ICT).
    Soldemo, Markus
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Weissenrieder, Jonas
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Gotelid, Mats
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Hammar, Mattias
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Auger recombination in In(Ga)Sb/InAs quantum dots2015In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 106, no 1, p. 013103-Article in journal (Refereed)
    Abstract [en]

    We report on the epitaxial formation of type II In0.5Ga0.5Sb/InAs and InSb/InAs quantum dot ensembles using metal organic vapor phase epitaxy. Employing scanning tunneling spectroscopy, we determine spatial quantum dot dimensions smaller than the de Broglie wavelength of InGaSb, which strongly indicates a three dimensional hole confinement. Photoluminescence spectroscopy at low temperatures yields an enhanced radiative recombination in the mid-infrared regime at energies of 170-200 meV. This luminescence displays a strong excitation power dependence with a blueshift indicating a filling of excited quantum dot hole states. Furthermore, a rate equation model is used to extract the Auger recombination coefficient from the power dependent intensity at 77 K yielding values of 1.35 x 10(-28) cm(6)/s for In0.5Ga0.5Sb/InAs quantum dots and 1.47 x 10(-27) cm(6)/s for InSb/InAs quantum dots, which is about one order of magnitude lower as previously obtained values for InGaSb superlattices.

1 - 12 of 12
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