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BaSnO3: thin film growth, transport properties, devices, and interfaces

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Authors

Useong Kim

Advisor
차국린
Issue Date
2015-08
Publisher
서울대학교 대학원
Keywords
BaSnO3
Description
학위논문(박사)--서울대학교 대학원 :자연과학대학 물리·천문학부,2015. 8. 차국린.
Abstract
Of great signi cance to the eld of oxide electronics is the discovery of an oxide material
possessing all the three important physical properties: the perovskite structure,
high oxygen stability, and high electron mobility. The perovskite structure implies novel
physical properties typically exempli ed by superconductivity or colossal magentoresistance;
the high oxygen stability ensures the bipolar dopability of oxide materials and
the reliability of devices made of them; the high electron mobility enables the triumph
of oxide materials over nitrides in the competition for high speed device applications. It
is BaSnO3 that ts for the description by judging from the cubic perovskite structure,
the thermal stability up to 1,000 C and the electron mobility as high as 320 cm2 V??1
s??1 in the metallic state.
Discussed in this dissertation will be the endeavors to understand and utilize the phyical
proprerties of BaSnO3 such as the growth of BaSnO3 epitaxial lms, the analyses of
the transport properties of the lms depending on the choices of dopants, the fabrication
of eld e ect devices based on BaSnO3, and the investigation of interfaces formed
between BaSnO3 and polar perovskite oxides. The BaSnO3 epitaxial lm growth on
SrTiO3 substrates has been successfully carried out by using the pulsed laser deposition
technique. The crystallinity of the lms has been investigated by X-ray di raction
analyses; the full width at half maximum of the !-rocking curves as narrow as 0.084
has proven that high-crystalline BaSnO3 lms can be grown on the lattice-mismatched
SrTiO3 substrates. Cross-sectional transmission electron spectroscopy and etch-pit developing
technique have been employed to inspect crystallographic defects or disorders in
the BaSnO3 lms and have revealed the density of threading dislocations to the amount
of 6 1010 cm??2.
The transport properties of electron-doped BaSnO3 epitaxial lms on the SrTiO3 substrates
have been studied in details with the relaxation time approximation in the electron
scattering theory. The semi-empirical analyses evince the dominance of the threading
dislocations among the sources of the conduction electron scattering and elucidate
the hampered electron mobility in the epitaxial lms ( 70 cm2 V??1 s??1). Lanthanum
is of an advantage that high electron mobility can be achieved in the BaSnO3 system
doped by it. But, it has been learned that lanthanum is likely to create the antisite
defects substituting the Sn-sites in lieu of the Ba-sites and trap up to about 3.7 1019
conduction electrons per cubic centimeters. Antimony, another dopant tried in order to
avoid the antisite problem, has provided the BaSnO3 epitaxial lms with even poorer
electron mobility ( 10 cm2 V??1 s??1). The electon a nity of antimony, the propensity of
antimony to migrate, and the charged cores of the threading dislocations work together
and create highly e ective defect clusters in scattering the conduction electrons.
The device fabrication has employed the metal-insulator-semiconductor structure where
a slightly doped BaSnO3 layer has been used as the semiconductor channel. Two insulator
materials, Al2O3 and LaInO3, have been tried to form interfaces with the channel.
At rst, an Al2O3/BaSnO3 transistor has been demonstrated with the device performances
far better than those of Al2O3/SrTiO3 and Al2O3/KTaO3 transistors. Especially,
the eld e ect mobility is two orders of higher in the Al2O3/BaSnO3 transistor.
Next, an LaInO3/BaSnO3 transistor has been fabricated with a heavily doped metallic
BaSnO3 layers used as the metal gate and contact terminals. The employment of
metallic BaSnO3 layers lets the transistor be composed exclusively of perovskite oxides.
The \all-perovskite transistor" has shown remarkable device performances: 90 cm2 V??1
s??1 of the eld e ect mobility, 107 of the current on/o ratio, and 0.65 V dec??1 of the
subthreshold swing. The eld e ect mobility of the LaInO3/BaSnO3 transistor is 18
times higher than that of the famous LaAlO3/SrTiO3 transistor at room temperature.
Last but not least, the conductive interface formation between LaInO3 and BaSnO3 has
been discussed in the context of polarity discontinuity at the interface. The 103 times of
enhancement in sheet conductance of La-doped BaSnO3 layer has been discovered, which
implies formation of two-dimensional electron gas by the interface formation only. The
enhanced sheet conductance reaches about the order of 10??4
??1 sq. The robustness
of the two-dimensional electron gas after oxygen annealing process and the lack of it in
the non-polar interface made of BaHfO3 or SrZrO3 and La-doped BaSnO3 layers, which
show the two-dimensional electron gas is formed exclusively by the polar interface, have
been con rmed. The investigation of the e ect of La concentration in La-doped BaSnO3
layer on the enhanced sheet conductance at the interface leads to the conclusion that
the origin of the two-dimensional electron gas at the interface is the accumulation of
electrons induced by the intrinsic polarization in the LaInO3 layer.
Language
eng
URI
http://dcollection.snu.ac.kr:80/jsp/common/DcLoOrgPer.jsp?sItemId=000000067527
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