18 research outputs found
Charge doping and large lattice expansion in oxygen-deficient heteroepitaxial WO3
Tungsten trioxide is a versatile material with widespread applications
ranging from electrochromic and optoelectronic devices to water splitting and
catalysis of chemical reactions. For technological applications, thin films of
WO3 are particularly appealing, taking advantage from high surface-to-volume
ratio and tunable physical properties. However, the growth of stoichiometric,
crystalline thin films is challenging because the deposition conditions are
very sensitive to the formation of oxygen vacancies. In this work, we show how
background oxygen pressure during pulsed laser deposition can be used to tune
the structural and electronic properties of WO3 thin films. By performing X-ray
diffraction and low-temperature transport measurements, we find changes in WO3
lattice volume up to 10%, concomitantly with an insulator-to-metal transition
as a function of increased level of electron doping. We use advanced ab initio
calculations to describe in detail the properties of the oxygen vacancy defect
states, and their evolution in terms of excess charge concentration. Our
results depict an intriguing scenario where structural, electronic, optical,
and transport properties of WO3 single-crystal thin films can all be purposely
tuned by a suited control of oxygen vacancies formation during growth
Balanced electron-hole transport in spin-orbit semimetal SrIrO3 heterostructures
Relating the band structure of correlated semimetals to their transport
properties is a complex and often open issue. The partial occupation of
numerous electron and hole bands can result in properties that are seemingly in
contrast with one another, complicating the extraction of the transport
coefficients of different bands. The 5d oxide SrIrO3 hosts parabolic bands of
heavy holes and light electrons in gapped Dirac cones due to the interplay
between electron-electron interactions and spin-orbit coupling. We present a
multifold approach relying on different experimental techniques and theoretical
calculations to disentangle its complex electronic properties. By combining
magnetotransport and thermoelectric measurements in a field-effect geometry
with first-principles calculations, we quantitatively determine the transport
coefficients of different conduction channels. Despite their different
dispersion relationships, electrons and holes are found to have strikingly
similar transport coefficients, yielding a holelike response under field-effect
and thermoelectric measurements and a linear, electronlike Hall effect up to 33
T.Comment: 5 pages, 4 figure
Phosphorus Molecules on Ge(001): A Playground for Controlled n‑Doping of Germanium at High Densities
The achievement of controlled high n-type doping in Ge will enable the fabrication of a number of innovative nanoelectronic and photonic devices. In this work, we present a combined scanning tunneling microscopy, secondary ions mass spectrometry, and magnetoÂtransport study to understand the atomistic doping process of Ge by P<sub>2</sub> molecules. Harnessing the one-dimer footprint of P<sub>2</sub> molecules on the Ge(001) surface, we achieved the incorporation of a full P monolayer in Ge using a relatively low process temperature. The consequent formation of P–P dimers, however, limits electrical activation above a critical donor density corresponding to P–P spacing of less than a single dimer row. With this insight, tuning of doping parameters allows us to repeatedly stack such 2D P layers to achieve 3D electron densities up to ∼2 × 10<sup>20</sup> cm<sup>–3</sup>