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 mm² glass substrates. The Schottky barrier contacts were fabricated by the reactive direct-current sputtering of platinum. Best diode properties (rectification ratio <i>S</i>_V = 2.7 × 10⁷, ideality factor η = 1.05, and effective barrier height ϕ_B,eff = 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>_V = 3.9 × 10⁷, η = 1.12, and ϕ_B,eff = 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 Al1−x O and Zn x Ga1−x 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 Al1−x O and Zn x Ga1−x 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 BiFeO₃–BaTiO₃ 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 BiFeO₃–BaTiO₃ 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 BiFeO₃–BaTiO₃. Surprisingly, the highest ME voltage coefficient of 55 V cm^–1 Oe^–1 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 BiFeO₃ 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 BaTiO₃ and BiFeO₃. 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