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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.
    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.

  • 3.
    Marcks von Würtemberg, Rickard
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Yu, Xingang
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Berggren, Jesper
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Hammar, Mattias
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Performance optimisation of epitaxially regrown 1.3-μm vertical-cavity surface-emitting lasers2009In: IET Optoelectronics, ISSN 1751-8768, Vol. 3, no 2, p. 112-121Article in journal (Refereed)
    Abstract [en]

    A number of GaAs-based long-wavelength, vertical-cavity, surface-emitting laser structures with optical and electrical confinement based on selective area epitaxy have been fabricated and evaluated. The influence on output power, threshold current, thermal stability and modal properties from design parameters such as bottom-distributed Bragg reflector (DBR) doping, cavity doping, dielectric top DBR design and carrier confinement barriers is evaluated. More than 7 mW of output power is emitted from multimode devices with a square active region size of 10 mm. Single-mode power from smaller devices is restricted to 1.5 mW because of a non-optimal cavity shape.

  • 4.
    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.

  • 5.
    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.

  • 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.
    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.

  • 7.
    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.

  • 8.
    Yu, Xingang
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Developments for Improved Performance Vertical-Cavity Surface Emitting Lasers2014Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The vertical-cavity surface-emitting laser (VCSEL) is a type of laser diode that emits light from the surface of the chip from which it is manufactured rather than from a cleaved edge as so far has been common for most telecommunication lasers. VCSEL’s low cost, high power efficiency and low power consumption properties make it a very attractive signal source for many applications such as fiber optical communication, optical interconnects, 3D sensing, absorption spectroscopy, laser printing, etc.

    In this work, we have developed and evaluated new designs and technologies for extending the performance of VCSELs based on the GaAs material system. A novel scheme for single-mode emission from large size VCSELs, with active region size up to 10 μm, is proposed and discussed. Oxide-free designs of the VCSEL structure either based on an epitaxially regrown p-n-p layer or a buried tunnel junction (BTJ) for lateral current confinement are fabricated and characterized; the latter scheme yielding significant dynamic and static performance improvement as compared to epitaxially regrown design. In addition, the first room-temperature operation of a heterojunction bipolar transistor (HBT) 980nm VCSEL, a so-called transistor-VCSEL, is demonstrated. This novel three-terminal operational VCSEL is believed to have the potential for a ultrahigh modulation bandwidth due to altered carrier dynamics in the cavity region.

  • 9.
    Yu, Xingang
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Chung, Il-Sug
    Mork, Jesper
    Xiang, Yu
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Berggren, Jesper
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Hammar, Mattias
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Single-mode InGaAs/GaAs 1.3-mu m VCSELs Based on a Shallow Intracavity Patterning2010In: SEMICONDUCTOR LASERS AND LASER DYNAMICS IV / [ed] Panajotov, K; Sciamanna, M; Valle, AA; Michalzik, R, 2010, Vol. 7720, p. 772021-Conference paper (Refereed)
    Abstract [en]

    A high-power single-mode 1.3-mu m InGaAs/GaAs vertical-cavity surface-emitting laser (VCSEL) structure employing a novel concept of engineering the optical mode profile to match the gain profile is suggested and demonstrated experimentally and theoretically. In contrast to various singlemode VCSEL approaches reported in the literature so far, based on selective loss or anti-resonant effects to suppress higher order modes, it is due to a novel design to increase the active region size while maintaining single mode emission. The shape of the fundamental mode profile is engineered to be similar to the gain profile which resembles a doughnut shape especially in intra-cavity contacted devices. In this way, the fundamental mode with the best fit to the gain profile can reach the lasing condition earliest and consume all the optical gain, leading to a suppression of higher order modes. Notably, despite this engineered shape of the mode profile, the far field shape remains close to Gaussian. The mode shaping can be achieved by introducing a shallow intracavity patterning before depositing the top mirror. Fabricated device structures consist of a A-Si/SiN/SiO(2) top mirror, modulation-doped current spreading layers, re-grown current confinement layers, three InGaAs/GaAs quantum wells, and a GaAs/AlGaAs bottom mirror. Single mode operation is demonstrated even for devices with active region as large as 10 mu m.

  • 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.

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