Thin-film transistors made of solution-processed metal oxide semiconductors hold great promise for application in the emerging sector of large-area electronics. However, further advancement of the technology is hindered by limitations associated with the extrinsic electron transport properties of the often defect-prone oxides. We overcome this limitation by replacing the single-layer semiconductor channel with a low-dimensional, solution-grown In₂O₃/ZnO heterojunction. We find that In₂O₃/ZnO transistors exhibit band-like electron transport, with mobility values significantly higher than single-layer In₂O₃ and ZnO devices by a factor of 2 to 100. This marked improvement is shown to originate from the presence of free electrons confined on the plane of the atomically sharp heterointerface induced by the large conduction band offset between In₂O₃ and ZnO. Our finding underscores engineering of solution-grown metal oxide heterointerfaces as an alternative strategy to thin-film transistor development and has the potential for widespread technological applications.

GaN nanowires have been grown by molecular beam epitaxy either catalyst-free or catalyst-induced by means of Ni seeds. Under identical growth conditions of temperature and V/III ratio, both types of GaN nanowires are of wurtzite structure elongated in the Ga-polar direction and are constricted by M-plane facets. However, the catalyst-induced nanowires contain many more basal-plane stacking faults and their photoluminescence is weaker. These differences can be explained as effects of the catalyst Ni seeds. Open image in new window

Atomically thin MoSe₂ films grown epitaxially on AlN by MBE have high crystallinity, smooth surface and interface morphology, and sizable semiconductor band gap for use in nanoelectronics.

On Si(1 1 1) and Si(0 0 1), GaN nanowires (NWs) form in a self-induced way without the need for any external material. On sapphire, NW growth is induced by Ni collectors. Both types of NWs exhibit the wurtzite crystal structure and grow in the Ga-polar C-direction perpendicular to the substrate. The NW sidewalls are M-plane facets, although on the Ni-induced NWs also A-plane segments form, if the growth temperature is low. Both self-induced and collector-induced NWs are free of strain and epitaxially aligned to the substrate, but in particular the former show a significant spread in tilt and twist caused by a mostly amorphous interfacial layer of Si-N. The self-induced NWs are virtually free of extended defects, but the collector-induced NWs contain many stacking faults. The photoluminescence of the former is significantly brighter and sharper. The spectra of single, dispersed, self-induced NWs contain extremely sharp excitonic lines. Significant emission is caused by excitons bound to donors close to the surface whose binding energy is reduced compared to the bulk value. In comparison, both the microstructure and optical properties of the self-induced NWs are superior. The limited material quality of the collector-induced NWs can be explained by detrimental effects of the collector.

We present a study of fully epitaxial Fe/Pt bilayers by means of ferromagnetic resonance (FMR) techniques. The dependence of the resonance field $H_{\mathrm{FMR}}$, the Gilbert damping parameter $\alpha$, and the FMR linewidth on the Pt thickness is presented and compared with reference layers. Since spin pumping is extremely sensitive to the interface properties, a corresponding study is of large importance. By studying fully epitaxial systems, the existence of an almost perfectly single-crystalline ordered interface is ensured. The measured effects, such as the dependence of the resonant field $H_{\mathrm{FMR}}$ on Pt thickness, are thus related to the physics of spin pumping and not to interface disorder effects. The damping parameter $\alpha$ has been extracted from the slope of the linewidth dependence on the FMR frequency. By measuring the enhancement of $\alpha$ with Pt a value for the effective spin mixing conductance of $g_{\mathrm{eff}}^{\uparrow \downarrow }=(4.9\pm 0.5)\times {10}^{19}{\mathrm{m}}^{-2}$ is obtained. We observe an opposite behavior in the dependence of $H_{\mathrm{FMR}}$ when compared with reports on YIG/Pt. In addition, the critical role of the proper choice of a reference layer for the estimation of this value is discussed.