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Register a new userEffective Carrier Doping and Metallization in LaxSr2-x-yBayIrO4-delta Thin Films
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We fabricate LaxSr2-x-yBayIrO4-delta thin films by pulsed laser deposition, in an effort to realize the effective carrier doping and metallization in the Sr2IrO4 system. We design ideal in-plane Ir-O-Ir frame structure by utilizing tensile substrate strain and Ba substitution, as well as control La doping and oxygen deficiency. This enables us to elucidate relation between the charge transport and the carrier density through systematic changes from original p-type spin-orbit Mott insulator to highly doped n-type metal.
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The interrelation between the epitaxial strain and oxygen deficiency in La0.7Ca0.3MnO3-{delta} thin films was studied in terms of structural and functional properties. The films with a thickness of 1000{AA} were prepared using a PLD system equipped with a RHEED facility and a pyrometric film temperature control. The epitaxial strain and the oxygen deficiency in the samples were systematically modified using three different substrates: SrTiO3, (LaAlO3)0.3-(Sr2AlTaO6)0.7 and LaSrAlO4, and four different oxygen pressures during film growth ranging from 0.27mbar to 0.1mbar. It could be demonstrated that the oxygen incorporation depends on the epitaxial strain: oxygen vacancies were induced to accommodate tensile strain whereas the compressive strain suppressed the generation of oxygen vacancies.
Heterostructures and superlattices consisting of a prototype Mott insulator, GdTiO3, and the band insulator SrTiO3 are grown by molecular beam epitaxy and show intrinsic electronic reconstruction, approximately 1/2 electron per surface unit cell at each GdTiO3/SrTiO3 interface. The sheet carrier densities in all structures containing more than one unit cell of SrTiO3 are independent of layer thicknesses and growth sequences, indicating that the mobile carriers are in a high concentration, two-dimensional electron gas bound to the interface. These carrier densities closely meet the electrostatic requirements for compensating the fixed charge at these polar interfaces. Based on the experimental results, insights into interfacial band alignments, charge distribution and the influence of different electrostatic boundary conditions are obtained.
We have performed soft x-ray spectroscopy in order to study the photoirradiation time dependence of the valence band structure and chemical states of layered transition metal nitride chloride TiNCl. Under the soft x-ray irradiation, the intensities of the states near the Fermi level (EF) and the Ti3+ component increased, while the Cl 2p intensity decreased. Ti 2p-3d resonance photoemission spectroscopy confirmed a distinctive Fermi edge with Ti 3d character. These results indicate the photo-induced metallization originates from deintercalation due to Cl desorption, and thus provide a new carrier doping method that controls the conducting properties of TiNCl.
Using electrically detected magnetic resonance spectroscopy, we demonstrate that doping the conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) with ethylene glycol allows for the control of effective local charge carrier hyperfine fields through motional narrowing. These results suggest that doping of organic semiconductors could enable the tuning of macroscopic material properties dependent on hyperfine fields such as magnetoresistance, the magneto-optical responses and spin-diffusion.
We report ultrafast surface pump and interface probe experiments on photoexcited carrier transport across single crystal bismuth films on sapphire. The film thickness is sufficient to separate carrier dynamics from lattice heating and strain, allowing us to investigate the time-scales of momentum relaxation, heat transfer to the lattice and electron-hole recombination. The measured electron-hole ($e-h$) recombination time is 12--26 ps and ambipolar diffusivity is 18--40 cm$^{2}$/s for carrier excitation up to $sim 10^{19} text{cm}^{-3}$. By comparing the heating of the front and back sides of the film, we put lower limits on the rate of heat transfer to the lattice, and by observing the decay of the plasma at the back of the film, we estimate the timescale of electron-hole recombination. We interpret each of these timescales within a common framework of electron-phonon scattering and find qualitative agreement between the various relaxation times observed. We find that the carrier density is not determined by the $e-h$ plasma temperature after a few picoseconds. The diffusion and recombination become nonlinear with initial excitation $gtrsim 10^{20} text{cm}^{-3}$.
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