Single and many-band effects in electron transport and energy relaxation in semiconductors: Dissertation

    Research output: ThesisDissertationCollection of Articles

    Abstract

    In this Thesis different aspects of band degree of freedom are explored in 2D electron transport and electron-phonon (e-ph) energy relaxation in 2D and 3D electron systems. Here the bands of interest are the conduction band valleys of many-valley semiconductors and spatial sub-bands of two-dimensional-electron gas in a quantum well. The experimental studies of electronic transport focus on double-gate SiO2-Si-SiO2 quantum well field-effect-transistors (FETs), which are fabricated utilizing silicon-on-insulator structures and wafer bonding. Double-gate FETs are intensively explored at the moment due to their prospects in microelectronics. The inclusion of a back gate electrode provides means to adjust the electron wave functions and the occupancy of the spatial 2D sub-bands. The contrast between single and two-sub-band transport is studied in low temperature conductivity/mobility and magneto transport. For example, the conductivity shows significant drop at the threshold of the second spatial sub-band due to inter-sub-band coupling and sub-band delocalization effect is observed at symmetric well potential. At room temperature several sub-bands are inevitably populated and the most relevant observed effect is the mobility enhancement towards symmetric quantum well potential. This mobility enhancement is one of the benefits of double-gate FETs in comparison to similar single-gate FETs. In the studies of e-ph energy relaxation we focus on the case where the phonons cannot directly couple the bands of the electron system. If the e-ph matrix elements depend on the band index then the band degree of freedom plays an important role. We developed a mean field theory, which allows elastic inter and intra-band scattering and also Coulomb interaction. Our model reproduces the long wavelength single-band energy loss rate results found in the literature. In the multi-band regime we find a set of new results, which suggest that the energy loss rate is strongly enhanced if the phonons couple asymmetrically to different bands and the single-band interaction is strongly screened. The effect is tested experimentally in heavily doped n-type Si samples by low temperature heating experiments. We find good agreement between the theory and experiment. Our findings enable a design of a novel electron-phonon heat switch.
    Original languageEnglish
    QualificationDoctor Degree
    Awarding Institution
    • Aalto University
    Supervisors/Advisors
    • Tulkki, Jukka, Supervisor, External person
    Award date19 Dec 2007
    Place of PublicationEspoo
    Publisher
    Print ISBNs978-951-38-7065-2
    Electronic ISBNs978-951-38-7066-9
    Publication statusPublished - 2007
    MoE publication typeG5 Doctoral dissertation (article)

    Fingerprint

    electrons
    energy
    field effect transistors
    quantum wells
    valleys
    phonons
    degrees of freedom
    energy dissipation
    conductivity
    augmentation
    theses
    microelectronics
    electron gas
    conduction bands
    switches
    insulators
    interactions
    wave functions
    wafers
    inclusions

    Keywords

    • two-dimensional electron gas
    • mobility
    • many-valley systems
    • electron-phonon interaction
    • SOI

    Cite this

    @phdthesis{c9a81f32c35947d6892abfcbf1986334,
    title = "Single and many-band effects in electron transport and energy relaxation in semiconductors: Dissertation",
    abstract = "In this Thesis different aspects of band degree of freedom are explored in 2D electron transport and electron-phonon (e-ph) energy relaxation in 2D and 3D electron systems. Here the bands of interest are the conduction band valleys of many-valley semiconductors and spatial sub-bands of two-dimensional-electron gas in a quantum well. The experimental studies of electronic transport focus on double-gate SiO2-Si-SiO2 quantum well field-effect-transistors (FETs), which are fabricated utilizing silicon-on-insulator structures and wafer bonding. Double-gate FETs are intensively explored at the moment due to their prospects in microelectronics. The inclusion of a back gate electrode provides means to adjust the electron wave functions and the occupancy of the spatial 2D sub-bands. The contrast between single and two-sub-band transport is studied in low temperature conductivity/mobility and magneto transport. For example, the conductivity shows significant drop at the threshold of the second spatial sub-band due to inter-sub-band coupling and sub-band delocalization effect is observed at symmetric well potential. At room temperature several sub-bands are inevitably populated and the most relevant observed effect is the mobility enhancement towards symmetric quantum well potential. This mobility enhancement is one of the benefits of double-gate FETs in comparison to similar single-gate FETs. In the studies of e-ph energy relaxation we focus on the case where the phonons cannot directly couple the bands of the electron system. If the e-ph matrix elements depend on the band index then the band degree of freedom plays an important role. We developed a mean field theory, which allows elastic inter and intra-band scattering and also Coulomb interaction. Our model reproduces the long wavelength single-band energy loss rate results found in the literature. In the multi-band regime we find a set of new results, which suggest that the energy loss rate is strongly enhanced if the phonons couple asymmetrically to different bands and the single-band interaction is strongly screened. The effect is tested experimentally in heavily doped n-type Si samples by low temperature heating experiments. We find good agreement between the theory and experiment. Our findings enable a design of a novel electron-phonon heat switch.",
    keywords = "two-dimensional electron gas, mobility, many-valley systems, electron-phonon interaction, SOI",
    author = "Mika Prunnila",
    note = "Project code: 16867",
    year = "2007",
    language = "English",
    isbn = "978-951-38-7065-2",
    series = "VTT Publications",
    publisher = "VTT Technical Research Centre of Finland",
    number = "666",
    address = "Finland",
    school = "Aalto University",

    }

    Single and many-band effects in electron transport and energy relaxation in semiconductors : Dissertation. / Prunnila, Mika.

    Espoo : VTT Technical Research Centre of Finland, 2007. 73 p.

    Research output: ThesisDissertationCollection of Articles

    TY - THES

    T1 - Single and many-band effects in electron transport and energy relaxation in semiconductors

    T2 - Dissertation

    AU - Prunnila, Mika

    N1 - Project code: 16867

    PY - 2007

    Y1 - 2007

    N2 - In this Thesis different aspects of band degree of freedom are explored in 2D electron transport and electron-phonon (e-ph) energy relaxation in 2D and 3D electron systems. Here the bands of interest are the conduction band valleys of many-valley semiconductors and spatial sub-bands of two-dimensional-electron gas in a quantum well. The experimental studies of electronic transport focus on double-gate SiO2-Si-SiO2 quantum well field-effect-transistors (FETs), which are fabricated utilizing silicon-on-insulator structures and wafer bonding. Double-gate FETs are intensively explored at the moment due to their prospects in microelectronics. The inclusion of a back gate electrode provides means to adjust the electron wave functions and the occupancy of the spatial 2D sub-bands. The contrast between single and two-sub-band transport is studied in low temperature conductivity/mobility and magneto transport. For example, the conductivity shows significant drop at the threshold of the second spatial sub-band due to inter-sub-band coupling and sub-band delocalization effect is observed at symmetric well potential. At room temperature several sub-bands are inevitably populated and the most relevant observed effect is the mobility enhancement towards symmetric quantum well potential. This mobility enhancement is one of the benefits of double-gate FETs in comparison to similar single-gate FETs. In the studies of e-ph energy relaxation we focus on the case where the phonons cannot directly couple the bands of the electron system. If the e-ph matrix elements depend on the band index then the band degree of freedom plays an important role. We developed a mean field theory, which allows elastic inter and intra-band scattering and also Coulomb interaction. Our model reproduces the long wavelength single-band energy loss rate results found in the literature. In the multi-band regime we find a set of new results, which suggest that the energy loss rate is strongly enhanced if the phonons couple asymmetrically to different bands and the single-band interaction is strongly screened. The effect is tested experimentally in heavily doped n-type Si samples by low temperature heating experiments. We find good agreement between the theory and experiment. Our findings enable a design of a novel electron-phonon heat switch.

    AB - In this Thesis different aspects of band degree of freedom are explored in 2D electron transport and electron-phonon (e-ph) energy relaxation in 2D and 3D electron systems. Here the bands of interest are the conduction band valleys of many-valley semiconductors and spatial sub-bands of two-dimensional-electron gas in a quantum well. The experimental studies of electronic transport focus on double-gate SiO2-Si-SiO2 quantum well field-effect-transistors (FETs), which are fabricated utilizing silicon-on-insulator structures and wafer bonding. Double-gate FETs are intensively explored at the moment due to their prospects in microelectronics. The inclusion of a back gate electrode provides means to adjust the electron wave functions and the occupancy of the spatial 2D sub-bands. The contrast between single and two-sub-band transport is studied in low temperature conductivity/mobility and magneto transport. For example, the conductivity shows significant drop at the threshold of the second spatial sub-band due to inter-sub-band coupling and sub-band delocalization effect is observed at symmetric well potential. At room temperature several sub-bands are inevitably populated and the most relevant observed effect is the mobility enhancement towards symmetric quantum well potential. This mobility enhancement is one of the benefits of double-gate FETs in comparison to similar single-gate FETs. In the studies of e-ph energy relaxation we focus on the case where the phonons cannot directly couple the bands of the electron system. If the e-ph matrix elements depend on the band index then the band degree of freedom plays an important role. We developed a mean field theory, which allows elastic inter and intra-band scattering and also Coulomb interaction. Our model reproduces the long wavelength single-band energy loss rate results found in the literature. In the multi-band regime we find a set of new results, which suggest that the energy loss rate is strongly enhanced if the phonons couple asymmetrically to different bands and the single-band interaction is strongly screened. The effect is tested experimentally in heavily doped n-type Si samples by low temperature heating experiments. We find good agreement between the theory and experiment. Our findings enable a design of a novel electron-phonon heat switch.

    KW - two-dimensional electron gas

    KW - mobility

    KW - many-valley systems

    KW - electron-phonon interaction

    KW - SOI

    M3 - Dissertation

    SN - 978-951-38-7065-2

    T3 - VTT Publications

    PB - VTT Technical Research Centre of Finland

    CY - Espoo

    ER -