6 research outputs found
Vital Role of Oxygen for the Formation of Highly Rectifying Schottky Barrier Diodes on Amorphous Zinc–Tin–Oxide with Various Cation Compositions
We
present electrical properties of Schottky barrier diodes on
room-temperature deposited amorphous zinc–tin–oxide
(ZTO) with Zn/(Zn + Sn) contents between 0.12 and 0.72. A combinatorial
approach with continuous composition spread pulsed laser deposition
is used to achieve the wide range of compositions with four samples
each on 50 × 50 mm<sup>2</sup> glass substrates. The Schottky
barrier contacts were fabricated by the reactive direct-current sputtering
of platinum. Best diode properties (rectification ratio <i>S</i><sub>V</sub> = 2.7 × 10<sup>7</sup>, ideality factor η
= 1.05, and effective barrier height ϕ<sub>B,eff</sub> = 1.25
eV) are obtained for a composition of 0.63 Zn/(Zn + Sn). Aging on
the timescale of days and months is observed that leads to improved
device properties (higher rectifications and lower ideality factors).
In particular, the diodes with the lowest performance in the as-prepared
state show the biggest improvements. The best diode properties after
the aging process (<i>S</i><sub>V</sub> = 3.9 × 10<sup>7</sup>, η = 1.12, and ϕ<sub>B,eff</sub> = 1.31 eV) were
also observed for 0.63 Zn/(Zn + Sn)
Additional file 2 of Low-Temperature PLD-Growth of Ultrathin ZnO Nanowires by Using Zn x Al1âx O and Zn x Ga1âx O Seed Layers
Figure S2. Scanning electron microscope images of the nanostructures for Ga-doped ZnO seed layers for all used temperatures and concentrations. (PDF 1105 kb
Additional file 1 of Low-Temperature PLD-Growth of Ultrathin ZnO Nanowires by Using Zn x Al1âx O and Zn x Ga1âx O Seed Layers
Figure S1. Scanning electron microscope images of the nanostructures for Al-doped ZnO seed layers for all used temperatures and concentrations. (PDF 1249 kb
Correlation of Interface Impurities and Chemical Gradients with High Magnetoelectric Coupling Strength in Multiferroic BiFeO<sub>3</sub>–BaTiO<sub>3</sub> Superlattices
The
detailed understanding of magnetoelectric (ME) coupling in multiferroic
oxide heterostructures is still a challenge. In particular, very little
is known to date concerning the impact of the chemical interface structure
and unwanted impurities that may be buried within short-period multiferroic
BiFeO<sub>3</sub>–BaTiO<sub>3</sub> superlattices during growth.
Here, we demonstrate how trace impurities and elemental concentration
gradients contribute to high ME voltage coefficients in thin-film
superlattices, which are built from 15 double layers of BiFeO<sub>3</sub>–BaTiO<sub>3</sub>. Surprisingly, the highest ME voltage
coefficient of 55 V cm<sup>–1</sup> Oe<sup>–1</sup> at
300 K was measured for a superlattice with a few atomic percent of
Ba and Ti that diffused into the nominally 5 nm thin BiFeO<sub>3</sub> layers, according to analytical transmission electron microscopy.
In addition, highly sensitive enhancements of the cation signals were
observed in depth profiles by secondary ion mass spectrometry at the
interfaces of BaTiO<sub>3</sub> and BiFeO<sub>3</sub>. As these interface
features correlate with the ME performance of the samples, they point
to the importance of charge effects at the interfaces, that is, to
a possible charge mediation of ME coupling in oxide superlattices.
The challenge is to provide cleaner materials and processes, as well
as a well-defined control of the chemical interface structure, to
push forward the application of oxide superlattices in multiferroic
ME devices
Dynamical Tuning of Nanowire Lasing Spectra
Realizing
visionary concepts of integrated photonic circuits, nanospectroscopy,
and nanosensing will tremendously benefit from dynamically tunable
coherent light sources with lateral dimensions on the subwavelength
scale. Therefore, we demonstrate an individual nanowire laser based
device which can be gradually tuned by reversible length changes of
the nanowire such that uniaxial tensile stress is applied to the respective
semiconductor gain material. By straining the device, the spontaneous
excitonic emission of the nanowire shifts to lower energies caused
by the bandgap reduction of the semiconductor. Moreover, the optical
gain spectrum of the nanolaser can be precisely strain-tuned in the
high excitation regime. The tuning of the emission does not affect
the laser threshold of the device, which is very beneficial for practical
applications. The applied length change furthermore adjusts the laser
resonances inducing a redshift of the longitudinal modes. Thus, this
concept of gradually and dynamically tunable nanolasers enables controlling
and modulating the coherent emission on the nanoscale without changing
macroscopic ambient conditions. This concept holds therefore huge
impact on nanophotonic switches and photonic circuit technology
Inhibition and Enhancement of the Spontaneous Emission of Quantum Dots in Micropillar Cavities with Radial-Distributed Bragg Reflectors
We present a micropillar cavity where nondesired radial emission is inhibited. The photonic confinement in such a structure is improved by implementation of an additional concentric radial-distributed Bragg reflector. Such a reflector increases the reflectivity in all directions perpendicular to the micropillar axis from a typical value of 15–31% to above 98%. An inhibition of the spontaneous emission of off-resonant excitonic states of quantum dots embedded in the microcavity is revealed by time-resolved experiments. It proves a decreased density of photonic states related to unwanted radial leakage of photons out of the micropillar. For on-resonance conditions, we find that the dot emission rate is increased, evidencing the Purcell enhancement of spontaneous emission. The proposed design can increase the efficiency of single-photon sources and bring to micropillar cavities the functionalities based on lengthened decay times