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Electronic materials: growth and characterisation
KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
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 [en]
Electrophysics, Photoemission, Ultra-short laser pulse, Thin film, Laser deposition, InSb, InAs, GaSb, Ferroelectrics
Keyword [sv]
Elektrofysik
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-144ISBN: 91-7283-967-8 (print)OAI: oai:DiVA.org:kth-144DiVA: diva2:7314
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
List of papers
1. Electron structure and electron dynamics at InSb(111)2×2 semiconductor surface
Open this publication in new window or tab >>Electron structure and electron dynamics at InSb(111)2×2 semiconductor surface
2003 (English)In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 76, no 3, 299-302 p.Article in journal (Refereed) Published
Abstract [en]

The conduction band electronic structure and the electron dynamics of the clean InSb(111)2 x 2 surface have been studied by laser based pump-and-probe photoemission. The results are compared to earlier studies of the InSb(110) surface. It is found that both the energy location and the time dependence of the photoexcited structures are very similar for the two surfaces. This indicates that the dominant part of the photoemission signal in the conduction band region is due to excitations of electrons in the bulk region and that the surface electronic states play a minor role. The fast decay of the excited state, tau similar to 12 ps, indicates that diffusion of hot electrons into the bulk is an important mechanism.

Keyword
Band structure, Carrier mobility, Electron scattering, Laser pulses, Laser tuning, Light emission, Photoelectron spectroscopy, Solid state lasers, Conduction band, Electron dynamics, Indium antimonide, Laser based pump-and-probe photoemission, Time and angle resolved photoelectron spectroscopy
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-4972 (URN)10.1007/s00339-002-1811-z (DOI)000179782100001 ()
Note
QC 20101015Available from: 2005-03-07 Created: 2005-03-07 Last updated: 2017-12-05Bibliographically approved
2. Anisotropy of electron structure at InAs(111) surfaces by laser pump-and-probe photoemission spectroscopy
Open this publication in new window or tab >>Anisotropy of electron structure at InAs(111) surfaces by laser pump-and-probe photoemission spectroscopy
Show others...
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. (

Keyword
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:nbn:se:kth:diva-8060 (URN)10.1016/j.susc.2004.10.018 (DOI)000226214400010 ()2-s2.0-10844273387 (Scopus ID)
Note
QC 20100810Available from: 2007-12-12 Created: 2007-12-12 Last updated: 2010-10-15Bibliographically approved
3. A bandgap surface state at the GaSb(001) surface observed by femtosecond laser pump-and-probe photoemission spectroscopy
Open this publication in new window or tab >>A bandgap surface state at the GaSb(001) surface observed by femtosecond laser pump-and-probe photoemission spectroscopy
Show others...
(English)Manuscript (Other academic)
Keyword
Laser methods, Angle resolved photoemission, Surface States, Gallium Antimonide, Photoelectron emission
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-4974 (URN)
Note
QC 20101015Available from: 2005-03-07 Created: 2005-03-07 Last updated: 2010-10-15Bibliographically approved
4. A new two-dimensional angle-resolving multi-anode electron detector for femtosecond photoemission spectroscopy
Open this publication in new window or tab >>A new two-dimensional angle-resolving multi-anode electron detector for femtosecond photoemission spectroscopy
Show others...
(English)Article in journal (Other academic) Submitted
Keyword
time-of-flight, angle-resolved photoemission spectroscopy, electron detector, femtosecond laser radiation
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-4975 (URN)
Note
QS 20120326Available from: 2005-03-07 Created: 2005-03-07 Last updated: 2012-03-26Bibliographically approved
5. High performance films of binary system SrTiO3-PbZr0.52Ti0.48O3 on sapphire
Open this publication in new window or tab >>High performance films of binary system SrTiO3-PbZr0.52Ti0.48O3 on sapphire
2001 (English)In: Integrated Ferroelectrics, ISSN 1058-4587, E-ISSN 1607-8489, Vol. 39, no 1-4, 351-358 p.Article in journal (Refereed) Published
Abstract [en]

Continuous series of solid solutions x.SrTiO3-(1-x).PbZr0.52Ti0.48O3 (SPZT) have been grown by pulsed laser deposition technique onto La0.7Sr0.3CoO3/Al2O3(01 (1) under bar2) single crystal. Films properties have been characterized in Au/SPZT/La0.7Sr0.3CoO3(LSCO)/Al2O3 vertical capacitive cell. X-ray diffraction shows SPZT/LSCO bilayer grows in strict epitaxial relationship with sapphire substrate: (001) SPZT parallel to (001) LSCO parallel to (01 (1) under bar2) Al2O3; [010] SPZT parallel to [010] LSCO parallel to [421] Al2O3. LSCO layer was found to be tensile strained, while SPZT film experiences tetragonal distortions c/a -1 approximate to 0.86% which are much lower than 2.73% in pure PZT ceramics. Curie temperature in SPZT film has been tailored continuously in the explored temperature range 77 K to 400 K by controlling SrTiO3:PZT ratio. Processing parameters have been optimized to get the highest tunability factor K = epsilon'(0) - epsilon'(V)/epsilon'(0) x 1/tandelta . SrTiO3:PZT=83:17 film exhibits superior properties: at I kHz maximum dielectric perinittivity and minimum loss tandelta were found to be 870 and 0.005, respectively; while K-factor exceeds value of 60 in the temperature range 280 to 350 degreesC reaching the maximum value of 64 at 325 degreesC. SPZT films can withstand prolonged pre-breakdown electric field and has resistivity as high as 3.5 10(12) Omega cm at 186 kV/cm.

Keyword
epitaxial films, tailoring ferroelectricity by alloying, low loss, voltage tunability, thin-films
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-21226 (URN)10.1080/10584580108011958 (DOI)000173066800038 ()
Note
QC 20100525Available from: 2010-08-10 Created: 2010-08-10 Last updated: 2017-12-12Bibliographically approved
6. Thin PZT film pressure microsensor
Open this publication in new window or tab >>Thin PZT film pressure microsensor
2001 (English)In: Materials Research Society Symposium Proceedings, ISSN 0272-9172, E-ISSN 1946-4274, Vol. 666, F8121-F8126 p.Article in journal (Refereed) Published
Abstract [en]

We report on a ferroelectric film pressure sensor fabricated on the top of 4 mm long and 1.4 mm in diameter Pt80Ir20 (PtIr) rod-shaped tip. It consists of a PZT(0.5 μm)/LSMO(0.1 μm) film heterostructure, deposited by pulsed laser ablation of stoichiometric ceramic targets PbZr0.52Ti0.48O3 and La0.67Sr0.33MnO3, and a circular, ∅ = 1.2 mm, Au electrode on the top of the PZT film. The Au/PZT/LSMO/PtIr thin-film capacitor demonstrates good ferroelectric properties: dielectric constant of 762 and loss tanδ =0.008 @ 5 kHz, induced polarization as high as 32 μC/cm2 at electric field of 250 kV/cm. Piezoelectric test, performed in a hydrostatic pressure chamber, exhibits the piezoelectric constant to be as high as 67 pC/N. This is 20% higher than 56 pC/N shown by a polarized bulk PZT sensor fabricated from the ceramics used as the target in the pulsed laser deposition process. Such an increase of the piezoelectric constant we attribute to the preferential (001) orientation of the PZT film grown on the PtIr bulk substrate. The resolution of the thin PZT film pressure microsensor was found to be about 1 mbar.

Keyword
Capacitors, Electrodes, Ferroelectric thin films, Film growth, Permittivity, Piezoelectric materials, Pressure measurement, Pulsed laser deposition, Pressure microsensors
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-4977 (URN)
Note
QC 20101015Available from: 2005-03-07 Created: 2005-03-07 Last updated: 2017-12-05Bibliographically approved
7. Characterization of heteroepitaxial Na0.5K0.5NbO3/La0.5Sr0.5CoO3 electro-optical cell
Open this publication in new window or tab >>Characterization of heteroepitaxial Na0.5K0.5NbO3/La0.5Sr0.5CoO3 electro-optical cell
2005 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 86, no 6, 062901-1-062901-3 p.Article in journal (Refereed) Published
Abstract [en]

Heteroepitaxial Na0.5K0.5NbO3(1.5 mum)/La0.5Sr0.5CoO3(0.5 mum) (NKN/LSCO) films were grown on an Al2O3(0112) single crystal (r-cut sapphire) by rf-magnetron sputtering (NKN) and pulsed laser deposition (LSCO) techniques. Prism coupling waveguide refractometry has been employed to characterize vertical capacitive electro-optical cells with 2 X 8 mm(2) semitransparent Au top electrodes. Fitting reflectivity spectra to Fresnel formulas yields extraordinary and ordinary refractive indices n(e) = 2.232 and n(o) = 2.234 as well as electro-optic coefficient r(13) = 17.4 pm/V. Dispersion of the refraction index follows the Sellmeier formula n(2) = 1 + 3.46/[1-(244 nm/lambda)(2)] in the range from 400 nm to 850 nm.

Keyword
na0.5k0.5nbo3 thin-films, chemical-vapor-deposition, pulsed-laser deposition, knbo3 single-crystal, growth, sapphire
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-14571 (URN)10.1063/1.1861121 (DOI)000227355200054 ()2-s2.0-18644386312 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
8. Na0.5K0.5NbO3 thin films for voltage controlled acoustoelectric device applications
Open this publication in new window or tab >>Na0.5K0.5NbO3 thin films for voltage controlled acoustoelectric device applications
2002 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 80, no 17, 3171-3173 p.Article in journal (Refereed) Published
Abstract [en]

Perovskite Na0.5K0.5NbO3 (NKN) thin films have been prepared on Y+36degrees cut single crystal quartz substrates using the pulsed laser ablation technique. X-ray diffraction theta-2theta and omega-scan data demonstrate almost perfectly c-axis oriented film textures with narrow mosaic broadening. Radio frequency dielectric spectroscopy showed that the films possess relatively high dielectric permittivities, low dielectric losses, and low frequency dispersions. Capacitance-voltage (C-V) measurements for a 2 mum slot NKN/quartz interdigital capacitor yield 23.1% tunability by applying 40 V bias at 1 MHz, while C-V hysteresis indicates polarization reversal. The considerable voltage tunability with superior crystallinity in piezoelectric NKN films on quartz substrates suggests their potential use for novel voltage tunable acoustoelectric devices.

Keyword
orientation
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-21483 (URN)10.1063/1.1473689 (DOI)000175144300047 ()
Note
QC 20100525Available from: 2010-08-10 Created: 2010-08-10 Last updated: 2017-12-12Bibliographically approved

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