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Register a new userZnO, ZnMnO and ZnCoO films grown by atomic layer deposition
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Despite many efforts the origin of a ferromagnetic (FM) response in ZnMnO and ZnCoO is still not clear. Magnetic investigations of our samples, not discussed here, show that the room temperature FM response is observed only in alloys with a non-uniform Mn or Co distribution. Thus, the control of their distribution is crucial for explanation of contradicted magnetic properties of ZnCoO and ZnMnO reported till now. In the present review we discuss advantages of the Atomic Layer Deposition (ALD) growth method, which enables us to control uniformity of ZnMnO and ZnCoO alloys. Properties of ZnO, ZnMnO and ZnCoO films grown by the ALD are discussed.
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In the present study we report on properties of ZnCoO films grown at relatively low temperature by the Atomic Layer Deposition, using two reactive organic zinc precursors (dimethylzinc and diethylzinc). The use of these precursors allowed us the significant reduction of a growth temperature to below 300oC. The influence of growth conditions on the Co distribution in ZnCoO films, their structure and magnetic properties was investigated using Secondary Ion Mass Spectroscopy, Scanning Electron Microscopy, Cathodoluminescence, Energy Dispersive X-ray Spectrometry (EDX), X-ray diffraction and Superconducting Quantum Interference Device magnetometry. We achieved high uniformity of the films grown at 160{deg}C. Such films are paramagnetic. Films grown at 200{deg} and at higher temperature are nonuniform. Formation of foreign phases in such films was detected using high resolution EDX method. These samples are not purely paramagnetic and show weak ferromagnetic response at low temperature.
We report on the structural, electrical and magnetic properties of ZnCoO thin films grown by Atomic Layer Deposition (ALD) method using reactive organic precursors of zinc and cobalt. As a zinc precursor we applied either dimethylzinc or diethylzinc and cobalt (II) acetyloacetonate as a cobalt precursor. The use of these precursors allowed us the significant reduction of a growth temperature to 300oC and below, which proved to be very important for the growth of uniform films of ZnCoO. Structural, electrical and magnetic properties of the obtained ZnCoO layers will be discussed based on the results of SIMS, SEM, EDS, XRD, AFM, Hall effect and SQUID investigations.
Atomic layer deposition was used to synthesize niobium silicide (NbSi) films with a 1:1 stoichiometry, using NbF5 and Si2H6 as precursors. The growth mechanism at 200oC was examined by in-situ quartz crystal microbalance (QCM) and quadrupole mass spectrometer (QMS). This study revealed a self-limiting reaction with a growth rate of 4.5 {AA}/cycle. NbSi was found to grow only on oxide-free films prepared using halogenated precursors. The electronic properties, growth rate, chemical composition, and structure of the films were studied over the deposition temperature range 150-400oC. For all temperatures, the films are found to be stoichiometric NbSi (1:1) with no detectable fluorine impurities, amorphous with a density of 6.65g/cm3, and metallic with a resistivity {rho}=150 {mu}{Omega}.cm at 300K for films thicker than 35 nm. The growth rate was nearly constant for deposition temperatures between 150-275oC, but increases above 300oC suggesting the onset of non-self limiting growth. The electronic properties of the films were measured down to 1.2K and revealed a superconducting transition at Tc=3.1K. To our knowledge, a superconducting niobium silicide film with a 1:1 stoichiometry has never been grown before by any technique.
We develop an InAs nanowire gate-all-around field-effect transistor using a transparent conductive zinc oxide (ZnO) gate electrode, which is in-situ atomic layer deposited after growth of gate insulator of Al2O3. We perform magneto-transport measurements and find a crossover from weak localization to weak antilocalization effect with increasing gate voltage, which demonstrates that the Rashba spin-orbit coupling is tuned by the gate electrode. The efficiency of the gate tuning of the spin-orbit interaction is higher than those obtained for two-dimensional electron gas, and as high as that for a gate-all-around nanowire metal-oxide-semiconductor field-effect transistor that was previously reported. The spin-orbit interaction is discussed in line with not only conventionally used one-dimensional model but also recently proposed model that considers effects of microscopic band structures of materials.
Palladium diselenide (PdSe$_2$), a new type of two-dimensional noble metal dihalides (NMDCs), has received widespread attention for its excellent electrical and optoelectronic properties. Herein, high-quality continuous centimeter-scale PdSe$_2$ films with layers in the range of 3L-15L were grown using Chemical Vapor Deposition (CVD) method. The absorption spectra and DFT calculations revealed that the bandgap of the PdSe$_2$ films decreased with increasing number of layers, which is due to PdSe$_2$ enhancement of orbital hybridization. Spectroscopic ellipsometry (SE) analysis shows that PdSe2 has significant layer-dependent optical and dielectric properties. This is mainly due to the unique strong exciton effect of the thin PdSe$_2$ film in the UV band. In particular, the effect of temperature on the optical properties of PdSe$_2$ films was also observed, and the thermo-optical coefficients of PdSe$_2$ films with different number of layers were calculated. This study provides fundamental guidance for the fabrication and optimization of PdSe$_2$-based optoelectronic devices.
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