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 -