High-crystalline GaSb epitaxial films grown on GaAs(001) substrates by low-pressure metal–organic chemical vapor deposition

Orthogonal experiments of Ga Sb films growth on Ga As(001)substrates have been designed and performed by using a low-pressure metal–organic chemical vapor deposition(LP-MOCVD)system.The crystallinities and microstructures of the produced films were comparatively analyzed to achieve the optimum growth parameters.It was demonstrated that the optimized Ga Sb thin film has a narrow full width at half maximum(358 arc sec)of the(004)ω-rocking curve,and a smooth surface with a low root-mean-square roughness of about 6 nm,which is typical in the case of the heteroepitaxial single-crystal films.In addition,we studied the effects of layer thickness of Ga Sb thin film on the density of dislocations by Raman spectra.It is believed that our research can provide valuable information for the fabrication of high-crystalline Ga Sb films and can promote the integration probability of mid-infrared devices fabricated on mainstream performance electronic devices.     

Angular momentum limitation of cluster emission from the compound nucleus: 16O(16O, α)28Si and 16O(16O, 8Be)24Mg

Excitation functions of the (¹⁶O, α) and (¹⁶O, ⁸Be) compound reactions on ¹⁶O have been measured and compared with Hauser-Feshbach model calculations. Using transmission coefficients for penetration of the real potential barrier in the exit channels we find global agreement, in contrast to systematic deviations obtained with optical-model transmission coefficients.     

Carbon nanotube diameter tuning using hydrogen amount and temperature on SiO2/Si substrates

Carbon nanotubes (CNTs) were grown on thin iron (Fe) films on SiO₂/Si substrates by chemical vapor deposition (CVD) at four different hydrogen (H₂)/methane (CH₄) ratios at temperatures ranging from 925 to 1000°C. The effects of temperature and the amount of hydrogen gas on the mean diameter at increasing temperature were examined. We demonstrated that the mean diameter and its distribution depend not only on temperature but also on the H₂ amount. We showed that increasing H₂ amount strongly affects the structure of CNTs, especially at high growth temperature; the mean diameter at 1000°C reduced from about 383 to 34 nm by increasing H₂ amount from 24 to 50 sccm. We observed that at high temperature growth the mean diameter was decreasing very fast initially with increasing H₂ amount suggesting the dominance of H₂ over the growth temperature. A decrease in the slope of diameter vs. H₂ amount with further increment in H₂ amount implied that the temperature was, then, deciding the CNT diameter through catalyst particle coarsening. The statistical analysis presented implies that the H₂ amount has to be adjusted according to the growth temperature for given CH₄ amount to keep CNT diameter under control, and the large diameter distributions at high temperature and high H₂ amount can be associated with the large variation in the catalyst particle sizes.     

Multi-wafer 3C—SiC heteroepitaxial growth on Si(100) substrates

<正>Epitaxial growth of semiconductor films in multiple-wafer mode is under vigorous development in order to improve yield output to meet the industry increasing demands.Here we report on results of the heteroepitaxial growth of multi-wafer 3C-SiC films on Si(100) substrates by employing a home-made horizontal hot wall low pressure chemical vapour deposition(HWLPCVD) system which was designed to be have a high-throughput,multi-wafer(3×2-inch) capacity. 3C-SiC film properties of the intra-wafer and the wafer-to-wafer including crystalline morphologies,structures and electronics are characterized systematically.The undoped and the moderate NH3 doped n-type 3C-SiC films with specular surface are grown in the HWLPCVD,thereafter uniformities of intra-wafer thickness and sheet resistance of the 3C-SiC films are obtained to be 6%~7%and 6.7%~8%,respectively,and within a run,the deviations of wafer-to-wafer thickness and sheet resistance are less than 1%and 0.8%,respectively.     

Heteroepitaxial growth of InP/GaAs(100) by metalorganic chemical vapor deposition

Using two-step method InP epilayers were grown on GaAs(100)substrates by low-pressure metalorganic chemical vapor deposition(LP-MOCVD).X-ray diffraction(XRD)and room-temperature(RT)photolu- minescence(PL)were employed to characterize the quality of InP epilayer.The best scheme of growing InP/GaAs(100)heterostructures was obtained by optimizing the initial low-temperature(LT)InP growth conditions,investigating the effects of thermal cycle annealing(TCA)and strained layer superlattice(SLS) on InP epilayers.Compared with annealing,10-periods Ga_(0.1)In_(0.9)P/InP SLS inserted into InP epilayers can improve the quality of epilayers dramatically,by this means,for 2.6-μm-thick heteroepitaxial InP,the full-widths at half-maximum(FWHMs)of XRDωandω-2θscans are 219 and 203 arcsec,respectively,the RT PL spectrum shows the band edge transition of InP,the FWHM is 42 meV.In addition,the successful growth of InP/In_(0.53)Ga_(0.47)As MQWs on GaAs(100)substrates indicates the quality of device demand of InP/GaAs heterostructures.     

Synthesis of large-scale GaN nanowires by ammoniating Ga2O3 films on Co layer deposited on Si（111） substrates

A mass of GaN nanowires has been successfully synthesized on Si（111） substrates by magnetron sputtering through ammoniating Ga2O3/Co films at 950℃. X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscope and Fourier transformed infrared spectra are used to characterize the samples. The results demonstrate that the nanowires are of single-crystal GaN with a hexagonal wurtzite structure and possess relatively smooth surfaces. The growth mechanism of GaN nanowires is also discussed.     

Low temperature improvement method on characteristics of Ba(Zr0.1Ti0.9)O3 thin films deposited on indium tin oxide/glass substrates

To improve the electrical properties of as-deposited BZ1T9 ferroelectric thin films, the supercritical carbon dioxide fluid (SCF) process were used by a low temperature treatment. In this study, the BZ1T9 ferroelectric thin films were post-treated by SCF process which mixed with propyl alcohol and pure H₂O. After SCF process treatment, the remnant polarization increased in hysteresis curves, and the passivation of oxygen vacancy and defect in leakage current density curves were found. Additionally, the improvement qualities of as-deposited BZ1T9 thin films after SCF process treatment were carried out XPS, C–V, and J–E measurements.     

Adsorption and organisation of para-hexaphenyl molecules on Si(100)

Para-hexaphenyl molecules (p-6P: C₃₆H₂₆) can be grown as nanofibres on various surfaces having optical properties of technological relevance. We report here the first observations of the initial stages of adsorption of individual p-6P molecules on Si(100)-(2×1) using room temperature Scanning Tunnelling Microscopy (STM). Depending on the substrate temperature, the hexaphenyl molecules adsorb in two configurations; indicating both weak and strong chemisorption. All six phenyl rings are clearly visible and the molecules are found to adsorb with characteristic angles between the long axis of the molecule and the silicon dimer rows. A statistical analysis of the spatial distribution of the molecules suggests that the clustering required for crystallographic nanofibre growth does not occur at the atomic scale under the experimental conditions used here.     

Influence of oxygen pressure on the ferroelectric properties of BiFeO3 thin films on LaNiO3/Si substrates via laser ablation

BiFeO₃(BFO) thin films of about 200 nm in thickness have been successfully grown on oxide bottom electrode, LaNiO₃(LNO), via pulsed laser ablation. X-ray diffraction spectrum of the as-deposited BFO film reveals a (100) preferred textured structure. The morphology of the BFO film is found to be strongly dependent on oxygen partial pressure in laser ablation. A saturated hysteresis loop with remanent polarization of 42 μC/cm² and coercive field of 100 kV/cm is obtained at the film deposition at 50 mTorr. The dielectric properties have also been obtained based on the influence of the oxygen pressure.     

Strain relaxation in epitaxial GaAs/Si (0 0 1) nanostructures

Abstract

Crystal defects, present in ~100 nm GaAs nanocrystals grown by metal organic vapour phase epitaxy on top of (0 0 1)-oriented Si nanotips (with a tip opening 50–90 nm), have been studied by means of high-resolution aberration-corrected high-angle annular dark-field scanning transmission electron microscopy. The role of 60° perfect, 30° and 90° Shockley partial misfit dislocations (MDs) in the plastic strain relaxation of GaAs on Si is discussed. Formation conditions of stair-rod dislocations and coherent twin boundaries in the GaAs nanocrystals are explained. Also, although stacking faults are commonly observed, we show here that synthesis of GaAs nanocrystals with a minimum number of these defects is possible. On the other hand, from the number of MDs, we have to conclude that the GaAs nanoparticles are fully relaxed plastically, such that for the present tip sizes no substrate compliance can be observed.     

Ni/Ag Schottky contacts on Al0.11Ga0.89N grown on Si (1 1 1) substrate by plasma-assisted MBE

Al_0.11Ga_0.89N/GaN samples are grown by plasma-assisted molecular beam epitaxy method on (1 1 1) silicon substrates. High purity gallium (7N) and aluminum (6N5) were used to grow Al_0.11Ga_0.89N, GaN, and AlN, respectively. The surface morphology, structural and optical properties of the sample has been investigated by scanning electron microscope (SEM), and high-resolution X-ray diffraction (HR-XRD), respectively. HR-XRD measurement showed that the sample has a typical diffraction pattern of hexagonal Al_0.11Ga_0.89N/GaN heterostructures. Ni/Ag bilayers are deposited on Al_0.11Ga_0.89N as the Schottky contacts. The effect of annealing in oxygen ambient on the electrical properties of Ni/Ag/Al_0.11Ga_0.89N is studied by current–voltage measurement. The annealing at a temperature of 700 °C for 10?min results in an increase in the ideality factor from 1.033 to 1.042 and an increase in the Schottky barrier height from 0.708 to 0.811 eV. Furthermore, the annealing in oxygen ambient also leads to an increase in the surface roughness of the contacts from 0.0098 to 0.1360 μm which is in agreement with the SEM results.     

Influence of Zr and Ce doping on electromagnetic properties of (Gd,Y)–Ba–Cu–O superconducting tapes fabricated by metal organic chemical vapor deposition

(Gd,Y)Ba₂Cu₃O_x tapes have been fabricated by metal organic chemical vapor deposition (MOCVD) with Zr-doping levels of 0–15 mol.% and Ce doping levels of 0–10 mol.% in 0.4 μm thick films. The critical current density (J_c) of Zr-doped samples at 77 K, 1 T applied in the orientation of H 6 c is found to increase with Zr content and shows a maximum at 7.5% Zr doping. The 7.5% Zr-doped sample exhibits a critical current density (J_c) of 0.95 MA/cm² at H 6 c which is more than 70% higher than the J_c of the undoped sample. The peak in J_c at H 6 c is 83% of that at H 6 a–b in the 7.5% Zr-doped sample which is more than twice as that in the undoped sample. Superconducting transition temperature (T_c) values as high as about 89 K have been achieved in samples even with 15% Zr and 10% Ce. Ce-doped samples with and without Ba compensation are found to exhibit substantially different J_c values as well as angular dependence characteristics.     

Intense terahertz emission from undoped GaAs/n-type GaAs and?InAs/AlSb structures grown on Si substrates in the transmission-geometry excitation

Intense terahertz radiation was generated from femtosecond laser-irradiated InAs and GaAs layers on Si substrates. Results show that InAs/Si and GaAs/Si films can be excited in reflection and transmission geometries. The InAs/Si film exhibited weaker emission for both excitation cases but it will be more feasible as a spectroscopic THz source due to the absence of complex spectral features in its emission spectrum. The GaAs/Si emission is characterized by Fabry?CPerot oscillations but it is 90% of that of p-InAs bulk crystal emission intensity in the reflection geometry. Excitation fluence measurements showed that the InAs/Si film saturates easily due to the laser??s shallow penetration depth in InAs.     

Magnetic-dichroism study of iron silicides formed at the Fe/Si(100) interface

The interplay between the phase composition, electronic structure, and magnetic properties of the Fe/Si(100)2×1 interface has been studied at the initial stages of its formation (at Fe doses up to 8 Å). The experiments were carried out in ultra high vacuum by using high-resolution photoelectron spectroscopy with synchrotron radiation. The interface magnetic properties were examined in terms of magnetic linear dichroism in angle-resolved Fe 3p core-level photoemission. It was found that at room temperature a disordered Fe–Si solid solution is formed at the first stage of Fe deposition (≤3.4 Å). In the coverage range of 3.4–4.3 Å the solid solution transforms into Fe₃Si. However, the in-plane ferromagnetic ordering of the silicide occurs only at 6.8 Å Fe that demonstrates the thickness dependence of the magnetic properties of Fe₃Si. The subsequent sample annealing to 150°C transforms Fe₃Si to ε-FeSi, leading to the disappearance of ferromagnetic behavior.     

Formation of hafnium carbide thin films by plasma enhanced chemical vapor deposition from bis(η-cyclopentadienyl)dimethylhafnium as precursor

Thin films of hafnium carbide have been deposited by plasma-enhanced chemical vapor deposition using bis(-cyclopentadienyl)dimethylhafnium, Cp₂ Hf(CH₃)₂, as precursor in 13.56 MHz planar reactor. The influence of the various experimental parameters on film properties has been studied. The carbon content ranged from 11 to 40 weight % and increased with the deposition rate. The film hardness varied between 1300 and 2000 HK. Depending on the carbon content and power delivered in the discharge, the film resistivity and film density ranged from 271 to 10⁵ ·cm and from 3.4 to 10.4 g/cm³, respectively, and the film composition varied from HfC to hafnium containing a-C: H films.     

α-Spectroscopic factor of Ogs from the C(O,C)O reaction

Elastic scattering angular distributions of ¹⁶O + ¹²C in the center of mass energy range from 8.55 MeV to 56.57 MeV have been analyzed considering the effect of the exchange of an alpha particle between projectile and target leading to the same nuclei of the entrance channel (elastic-transfer). An alpha particle spectroscopic factor for the ground state of the ¹⁶O was determined.     

Self-organized patterning on Si(001) by ion sputtering with simultaneous metal incorporation

This report focuses on the effect of simultaneous Fe incorporation in the self-organized pattern formation on Si(001) by low-energy ion-beam sputtering. Experimental observations giving evidence for the correlation between different ion-beam parameters, Fe concentration on the substrate, and the resulting topography are shown. It was observed that the incorporation of Fe affects the evolution of the topography and it is a requisite for the formation of ripples at near-normal incidence. It is shown also that Fe is not homogeneously distributed on the surface, but there is a higher concentration at the crests of the ripples than at the valleys. For the experimental setup used for this study, the Fe flux that reaches the surface is determined mainly by the acceleration voltage (U _acc), while the ion energy (E _ion) and ion-beam incidence angle (α) control the concentration of Fe in the steady state. The adjustment of these operational parameters of the ion source enables the fine-tuning of surface patterns.     

Thin TiO2 grown by metal–organic chemical vapor deposition on (NH4)2S x -treated InP

The electrical characteristics of thin TiO₂ films prepared by metal–organic chemical vapor deposition grown on a p-type InP substrate were studied. For a TiO₂ film of 4.7 nm on InP without and with ammonium sulfide treatment, the leakage currents are 8.8×10⁻² and 1.1×10⁻⁴ A/cm² at +2 V bias and 1.6×10⁻¹ and 8.3×10⁻⁴ A/cm² at −2 V bias. The lower leakage currents of TiO₂ with ammonium sulfide treatment arise from the improvement of interface quality. The dielectric constant and effective oxide charge number density are 33 and 2.5×10¹³ cm², respectively. The lowest mid-gap interface state density is around 7.6×10¹¹ cm⁻² eV⁻¹. The equivalent oxide thickness is 0.52 nm. The breakdown electric field increases with decreasing thickness in the range of 2.5 to 7.6 nm and reaches 9.3 MV/cm at 2.5 nm.