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GaAs based Vertical-Cavity Surface-Emitting Transistor-Lasers
KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The ever-increasing demand for broadband capacity of the global optical communication networks puts enormous requirements on the semiconductor laser used in the optical transmitter. Industrial standard bodies for optical communication project requirements of single-channel data rates as high as 100 Gbit/s around year 2020. This is a significant step with respect to today's technology which is only at the verge of introducing 25 Gbit/s emitters. The preferred light source for these applications is the vertical-cavity surface-emitting laser (VCSEL) which can offer cost- and power-efficient directly modulated operation. However, it has proven extremely difficult to push the modulation bandwidth of VCSELs beyond 30 GHz and radically new device concepts are demanded to meet the upcoming needs. One such new device paradigm consists of the transistor laser which is the fusion of a semiconductor laser and a high-speed heterojunction bipolar transistor (HBT) into a single device, with potential significant advantages in modulation bandwidth, noise properties and novel functionality by virtue of the three-terminal configuration. The present thesis deals with the design, fabrication and analysis of vertical-cavity surface-emitting transistor-lasers (T-VCSELs), a device previously not realized or investigated in great detail.

GaAs-based T-VCSELs are investigated both theoretically and experimentally. A three-dimensional model is set up with a commercial software package and used for performance predictions and analysis as well as design and optimization purposes. It is concluded that a T-VCSEL biased in the common-base configuration may have a bandwidth surpassing those of conventional diode-type VCSELs or a T-VCSEL itself in the common-emitter configuration. Fabricated T-VCSELs make use of an epitaxial regrowth design to homogeneously integrate an AlGaAs/GaAs HBT and an InGaAs/GaAs VCSEL. An intracavity contacting scheme involving all three terminals, undoped distributed Bragg reflectors and modulation doping are used to ensure a low-loss laser structure. The first generation of devices showed sub-mA range base threshold current in combination with a high output power close to 2 mW but did not fulfill the requirements for a fully operational transistor laser since the transistor went into saturation before the onset of lasing (IBsat<IBth). From numerical simulations this premature saturation was demonstrated being due to a lateral potential variation within the device and large voltage drops along the base and collector regions. As a remedy to this problem the base region was redesigned for a reduced resistance and transistor current gain, and the saturation current could thereby be extended well beyond threshold. These devices showed excellent transistor-laser characteristics with clear gain-compression at threshold, mA-range base threshold current, mW-range output power, high-temperature operation to at least 60°C, low collector-emitter offset voltage and record-low power dissipation during lasing. Furthermore, the collector-current breakdown characteristics was investigated in some detail and it is concluded that this, in contrast to previous models, presumably not is due to an intracavity photon reabsorption process but rather to a quantum-well band-filling effect.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. , vii, 64 p.
Series
TRITA-ICT/MAP AVH, ISSN 1653-7610 ; 2014:16
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-156841ISBN: 978-91-7595-363-2 (print)OAI: oai:DiVA.org:kth-156841DiVA: diva2:768029
Public defence
2014-12-19, Sal/hall C, Electrum, KTH-ICT, Kista, 10:00 (English)
Opponent
Supervisors
Note

QC 20141203

Available from: 2014-12-03 Created: 2014-12-02 Last updated: 2015-04-13Bibliographically approved
List of papers
1. Invited Paper: Design and modeling of a transistor vertical-cavity surface-emitting laser
Open this publication in new window or tab >>Invited Paper: Design and modeling of a transistor vertical-cavity surface-emitting laser
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2011 (English)In: Optical and quantum electronics, ISSN 0306-8919, E-ISSN 1572-817X, Vol. 42, no 11-13, 659-666 p.Article in journal (Refereed) Published
Abstract [en]

A multiple quantum well (MQW) transistor vertical-cavity surface-emitting laser (T-VCSEL) is designed and numerically modeled. The important physical models and parameters are discussed and validated by modeling a conventional VCSEL and comparing the results with the experiment. The quantum capture/escape process is simulated using the quantum-trap model and shows a significant effect on the electrical output of the T-VCSEL. The parameters extracted from the numerical simulation are imported into the analytic modeling to predict the frequency response and simulate the large-signal modulation up to 40 Gbps.

Keyword
Transistor laser, VCSEL, Numerical modeling, Quantum-trap model, Direct modulation
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-48519 (URN)10.1007/s11082-011-9444-0 (DOI)000296377000002 ()2-s2.0-80755163171 (Scopus ID)
Note

10th International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD) Location: Atlanta, GA Date: SEP 06-09, 2010. QC 20111202

Available from: 2011-12-02 Created: 2011-11-21 Last updated: 2017-12-08Bibliographically approved
2. Room-temperature operation of transistor vertical-cavity surface-emitting laser
Open this publication in new window or tab >>Room-temperature operation of transistor vertical-cavity surface-emitting laser
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2013 (English)In: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 49, no 3, 208-209 p.Article in journal (Refereed) Published
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.

National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-122993 (URN)10.1049/el.2012.4243 (DOI)000318542500030 ()2-s2.0-84877727168 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20130605

Available from: 2013-05-30 Created: 2013-05-30 Last updated: 2017-12-06Bibliographically approved
3. Minority current distribution in InGaAs/GaAs transistor-vertical-cavity surface-emitting laser
Open this publication in new window or tab >>Minority current distribution in InGaAs/GaAs transistor-vertical-cavity surface-emitting laser
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2013 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 102, no 19, 191101- p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2013
Keyword
current distribution, gallium arsenide, heterojunction bipolar transistors, III-V semiconductors, indium compounds, integrated optoelectronics, laser beams, laser cavity resonators, laser modes, numerical analysis, optical saturation, quantum wells, surface emitting lasers
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-122997 (URN)10.1063/1.4803175 (DOI)000320440800001 ()2-s2.0-84877935923 (Scopus ID)
Funder
Swedish Research Council, 2010-4386
Note

QC 20130626

Available from: 2013-05-30 Created: 2013-05-30 Last updated: 2017-12-06Bibliographically approved
4. Performance Optimization of GaAs-Based Vertical-Cavity Surface-Emitting Transistor-Lasers
Open this publication in new window or tab >>Performance Optimization of GaAs-Based Vertical-Cavity Surface-Emitting Transistor-Lasers
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2015 (English)In: IEEE Photonics Technology Letters, ISSN 1041-1135, E-ISSN 1941-0174, Vol. 27, no 7, 721-724 p.Article in journal, Letter (Refereed) Published
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.

Place, publisher, year, edition, pages
IEEE Press, 2015
Keyword
Semiconductor lasers, surface emitting lasers, transistor lasers
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-161188 (URN)10.1109/LPT.2015.2390298 (DOI)000350877700010 ()2-s2.0-84924873281 (Scopus ID)
Funder
Swedish Research Council, 2010-4386
Note

QC 20150312

Available from: 2015-03-09 Created: 2015-03-09 Last updated: 2017-12-04Bibliographically approved
5. Influence of base-region thickness on the performance of Pnp transistor-VCSEL
Open this publication in new window or tab >>Influence of base-region thickness on the performance of Pnp transistor-VCSEL
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2014 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 22, no 22, 27398-27414 p.Article in journal (Refereed) Published
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.

Keyword
Surface-Emitting Laser, Bipolar-Transistor, Operation
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-156833 (URN)10.1364/OE.22.027398 (DOI)000344004900093 ()2-s2.0-84919969277 (Scopus ID)
Funder
Swedish Research Council, 2010-4386
Note

QC 20141203

Available from: 2014-12-02 Created: 2014-12-02 Last updated: 2017-12-05Bibliographically approved
6. 1.3 μm Buried Tunnel junction InGaAs/GaAs VCSELs
Open this publication in new window or tab >>1.3 μm Buried Tunnel junction InGaAs/GaAs VCSELs
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2013 (English)Conference paper, Published 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.

National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-156836 (URN)
Conference
37th Workshop on Compound Semiconductor Device and Integrated Circuits held in Europe, Rostock, Germany
Note

QC 20141203

Available from: 2014-12-02 Created: 2014-12-02 Last updated: 2014-12-03Bibliographically approved
7. AlGaAs/GaAs/InGaAs pnp-type vertical-cavity surface-emitting transistor-lasers
Open this publication in new window or tab >>AlGaAs/GaAs/InGaAs pnp-type vertical-cavity surface-emitting transistor-lasers
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(English)Manuscript (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.

National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-156837 (URN)
Note

QS 2014

Available from: 2014-12-02 Created: 2014-12-02 Last updated: 2014-12-03Bibliographically approved

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Output format
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