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Anisotropy of electron structure at InAs(111) surfaces by laser pump-and-probe photoemission spectroscopy
KTH, School of Information and Communication Technology (ICT), Material Physics.
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.ORCID iD: 0000-0002-3086-9642
KTH, School of Information and Communication Technology (ICT), Material Physics.ORCID iD: 0000-0001-8669-6886
Optillion AB, Stockholm.
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2005 (English)In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 574, no 1, 89-94 p.Article in journal (Refereed) Published
Abstract [en]

The electronic structure and the electron dynamics of the clean InAs(111)A 2 x 2 and the InAs(111)B 1 x 1 surfaces have been studied by laser pump-and-probe photoemission spectroscopy. Normally unpopulated electron states above the valence band maximum (VBM) are filled on the InAs(111)A surface due to the conduction band pinning above the Fermi level (E-F). Accompanied by the downward band banding alignment, a charge accumulation layer is confined to the surface region creating a two dimensional electron gas (2DEG). The decay of the photoexcited carriers above the conduction band minimum (CBM) is originated by bulk states affected by the presence of the surface. No occupied states were found on the InAs(111)B 1 x 1 surface. This fact is suggested to be due to the surface stabilisation by the charge removal from the surface into the bulk. The weak photoemission intensity above the VBM on the (111)B surface is attributed to electron states trapped by surface defects. The fast decay of the photoexcited electron states on the (111)A and the (111)B surfaces was found to be tau(111A) less than or equal to 5 ps and tau(111B) less than or equal to 4ps, respectively. We suggest the diffusion of the hot electrons into the bulk is the decay mechanism. (

Place, publisher, year, edition, pages
2005. Vol. 574, no 1, 89-94 p.
Keyword [en]
Angle resolved photoemission; Indium arsenide; Laser methods; Surface electronic phenomena (work function, surface potential, surface states, etc.); Anisotropy; Electron energy levels; Electron gas; Fermi level; Heterojunctions; Molecular beam epitaxy; Photoemission; Indium compounds
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
URN: urn:nbn:se:kth:diva-8060DOI: 10.1016/j.susc.2004.10.018ISI: 000226214400010Scopus ID: 2-s2.0-10844273387OAI: oai:DiVA.org:kth-8060DiVA: diva2:13281
Note
QC 20100810Available from: 2007-12-12 Created: 2007-12-12 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Adatoms, Quasiparticles & Photons: The Multifaceted World of Photoelectron Spectroscopy
Open this publication in new window or tab >>Adatoms, Quasiparticles & Photons: The Multifaceted World of Photoelectron Spectroscopy
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The experimental work presented in this thesis is based on a wide assortment of very advanced and highly sophisticated photoelectron spectroscopy (PES) techniques. The objective of the present study has been to reveal and understand the electronic structure and electron dynamics in a broad spectrum of materials, ranging from wide band gap oxides, via semiconductors along with metals, and finally high-temperature superconductors.

The first part of the thesis concerns laser-based pump-and-probe PES. This unique experimental technique has permitted a study of the excited electronic structure and the electron dynamics of several semiconductor surfaces. An insight into details of the adatom to restatom charge-transfer of the Ge(111)c(2x8) surface is presented, as well as an estimate for the timescale in which the dynamic adatoms of the Ge(111):Sn(sqrt3xsqrt3)R30deg surface operate. Further results comprise a novel unoccupied surface state at the GaSb(001) surface as well as a time-resolved study of the charge accumulation layer at the InAs(111)A/B surfaces.

In the second part, high-resolution synchrotron based angle-resolved PES (ARPES) data from the cuprate high-temperature superconductor La(2-x)Sr(x)CuO(4) (LSCO) is presented. This extensive study, reveals detailed information about how the Fermi surface and electronic excitations evolve with doping in the superconducting state. The results comprise support for a connection between high- and low-energy electronic responses, the characteristics of the superconducting gap, and indication of a quantum phase transition between two different superconducting phases.

In the third group of experiments we move away from the two-dimensional systems and concentrate on fully three-dimensional compounds. By the use of soft x-ray ARPES it is possible to extract the three-dimensional electronic structure in a straightforward manner with increased k(perpendicular)-resolution. As a result the first high-quality ARPES data from Cu2O is presented, as well as a novel method for extracting the (real space) electron density by ARPES. These experiments clearly display the advantages of using soft x-ray ARPES. If the material and type of experiment is chosen wisely, the benefit of the increased k||-window and the free electron final state, surpass the drawbacks of decreased count-rate and inferior energy resolution. Finally we return to the high-temperature superconductors (NCCO & Nd-LSCO) and make use of the increased bulk-sensitivity. From an evident change in the shape of the Fermi surface when moving from low to high photon energies, the durface to bulk difference in electronic structure is highlighted.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. xvi, 54 p.
Series
Trita-ICT/MAP, 2007:12
Keyword
angle-resolved photoelectron spectroscopy, electronic structure, electron dynamics, semiconductor surfaces, oxides, high-temperature superconductors
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-4659 (URN)978-91-7178-822-1 (ISBN)
Public defence
2007-12-13, N1, Isafjordsgatan 28 A/D, Kista, 10:15
Opponent
Supervisors
Note
QC 20100810Available from: 2007-12-12 Created: 2007-12-12 Last updated: 2010-08-10Bibliographically approved
2. Electronic materials: growth and characterisation
Open this publication in new window or tab >>Electronic materials: growth and characterisation
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

In this thesis the InSb(111), InAs(111) and GaSb(001) surfaces have been studied by means of time- and angle-resolved photoemission spectroscopy based upon the femtosecond laser system. The pump-and-probe technique allows to analyse both electron states in the valence band and normally unpopulated electron states above the valence band, which can be occupied by transiently excited carriers at the optically pumped surface. The life time of excited carriers is analysed by controlling over the time delay between pump and probe pulses. Experimental studies of the InSb(111) surface and comparison with a previously studied InSb(110) surface show electron excitations in the bulk region with a minor surface contribution. Time-resolved experiments of carrier dynamics at the polar InAs(111)A and InAs(111)B surfaces show about the same life time of excited carriers, while no populated states above the valence band maximum have been found at the InAs(111)A due to the charge removal. Surface intergap electron states have been found at the GaSb(001) surface located at ~250 meV above the valence band maximum. Angle-resolved experiments showed a strong confinement of this state at the centre of the surface Brillouin zone.

A new two dimensional angle-resolved multi-anode analyser for the femtosecond laser photoemission setup has been constructed. The analyser can resolve a cone opening angle of ~1º at a drift distance of ~0.5 m with an energy resolution of ~125 meV.

A continuous series of binary system SrTiO3–PbZr0.52Ti0.48O3 has been grown by pulsed laser deposition (PLD) on sapphire substrate with crystalline quality control by x-ray diffraction (XRD). The maximum tunability has been tailored to room temperature, where STO�PZT (71/29) composition shows superior performance. A PbZr0.52Ti0.48O3 thin film pressure sensor has been fabricated by PLD and characterised by XRD and electrical measurements. The piezoelectric constant was found to be ~20 % higher compared to the bulk ceramics. A ferroelectric thin film electro-optical cell Na0.5K0.5NbO3/La0.5Sr0.5CoO3 (NKN/LSCO) on sapphire has been fabricated by PLD. Refractive indices and electro-optical coefficient of the cell were characterised by prism coupling refractometry. The tunability of the PLD fabricated 2 μm slot NKN thin film interdigital capacitor has been found ~23 % at 40 V bias voltage and frequency 1 MHz.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. vii, 80 p.
Series
Trita-FYS, ISSN 0280-316X ; 3077
Keyword
Electrophysics, Photoemission, Ultra-short laser pulse, Thin film, Laser deposition, InSb, InAs, GaSb, Ferroelectrics, Elektrofysik
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-144 (URN)91-7283-967-8 (ISBN)
Public defence
2005-03-18, Kollegiesalen, Valhallavägen 79, Stockholm, 10:15
Opponent
Supervisors
Note
QC 20101015Available from: 2005-03-07 Created: 2005-03-07 Last updated: 2010-10-15Bibliographically approved

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Tjernberg, OscarKarlsson, Ulf O.

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