Use Of Vicinal Substrates Research Articles

Dislocation reduction mechanism os GaN films on vicinal sapphire substrates

<sec>GaN materials are widely used in optoelectronic devices, high-power devices and high-frequency microwave devices because of their excellent characteristics, such as wide frequency band, high breakdown electric field, high thermal conductivity, and direct band gap. Owing to the large lattice mismatch and thermal mismatch brought by the heterogeneous epitaxy of GaN material, the GaN epitaxial layer will produce a great many dislocations in the growth process, resulting in the poor crystal quality of GaN material and the difficulty in further improving the device performance. Therefore, researchers have proposed the use of vicinal substrate to reduce the dislocation density of GaN material, but the dislocation annihilation mechanism in GaN film on vicinal substrate has not been sufficiently studied. Therefore, in this paper, GaN thin films are grown on vicinal sapphire substrates at different angles by using metal organic chemical vapor deposition technique. Atomic force microscope, high resolution X-ray diffractometer, photoluminescence testing, and transmission electron microscopy are used to analyze in detail the effects of vicinal substrates on GaN materials. The use of vicinal substrates can significantly reduce the dislocation density of GaN materials, but lead to degradation of their surface morphology morphologies. And the larger the substrate vicinal angle, the lower the dislocation density of the sample is. The dislocation density of the sample with a 5º bevel cut on the substrate is reduced by about one-third compared to that of the sample with a flat substrate. The special dislocation termination on the mitered substrate is observed by transmission electron microscopy, which is one of the main reasons for the reducing the dislocation density on the mitered substrate. The step merging on the vicinal sapphire substrate surface leads to both transverse growth and longitudinal growth of GaN in the growth process. The transverse growth region blocks the dislocations, resulting in an abrupt interruption of the dislocations during propagation, which in turn reduces the dislocation density.</sec><sec>Based on the above phenomena, a model of GaN growth on vicinal substrate is proposed to explain the reason why the quality of GaN crystal can be improved by vicinal substrate.</sec>

Unidirectional lateral nanowire formation during the epitaxial growth of GaAsBi on vicinal substrates

We report on enhanced control of the growth of lateral GaAs nanowires (NWs) embedded in epitaxial (100) GaAsBi thin films enabled by the use of vicinal substrates and the growth-condition dependent role of Bi as a surfactant. Enhanced step-flow growth is achieved through the use of vicinal substrates and yields unidirectional nanowire growth. The addition of Bi during GaAsBi growth enhances Ga adatom diffusion anisotropy and modifies incorporation rates at steps in comparison to GaAs growth yielding lower density but longer NWs. The NWs grown on vicinal substrates grew unidirectionally towards the misorientation direction when Bi was present. The III/V flux ratio significantly impacts the size, shape and density of the resulting NWs. These results suggest that utilizing growth conditions which enhance step-flow growth enable enhanced control of lateral nanostructures.

Effect of substrate orientation on strain relaxation mechanisms of InGaAs layer grown on vicinal GaAs substrates measured by in situ X-ray diffraction

The effect of substrate orientation on strain relaxation mechanisms of an InGaAs layer grown on vicinal GaAs substrates was investigated by in situ X-ray diffraction (XRD). The crystallographic tilt and indium segregation in the InGaAs layer were altered depending on the miscut direction and angle. In the case of the substrate tilted 6° toward the [110] direction, one type of misfit dislocations was formed preferentially rather than other types, especially in the rapid relaxation phase. While in the case of the substrate tilted 6° toward the direction, no anisotropies during relaxation were observed. The present finding indicates that the appropriate use of vicinal substrates may lead to a novel method of improving the crystal quality of heterolayers.

Kinetic Monte Carlo simulation of quantum dot growth on stepped substrates

The growth of quantum dots (QDs) on various Si platforms often results in a bimodal distribution for the size of the QD. This has been previously attributed to the use of vicinal substrates. In this study, a kinetic Monte Carlo (KMC) simulation using a double-zone model is used to study the formation of QDs on the stepped substrate. In this double-zone model, the substrate is divided into two regions, the step region and the terrace region. An additional activation barrier of Estep is introduced for adatoms diffusing in the step region. Preferential nucleation at the step region was observed and the dot size distribution uniformity depends on the growth temperature and the magnitude of Estep.

Growth Aspects of Thin-Film Composite Heterostructures of Oxide Multicomponent Perovskites for Electronics

We review, based on our results, the problems and solutions for the growth of thin films and composite heterostructures emphasizing the general growth aspects and principles vs specifics for each material or heterostructure. The materials used in our examples are Bi2Sr2Ca2Cu3O10, Bi2Sr2CaCu2O8, YBa2Cu3O7, (Sr, Ca)CuO2, (Ba, Ca)CuO2, and Bi4Ti3O12. The growth method was metal organic chemical vapor deposition (MOCVD). The presented thin films or heterostructures have c- and non-c-axis orientations. We discuss the implications of the film–substrate lattice relationships, paying attention to film–substrate lattice mismatch anisotropy and to film–film lattice mismatch, which has a significant influence on the quality of the non-c-axis heterostructures. We also present growth control through the use of vicinal substrates and two-temperature (template) and interrupted growth routes allowing significant quality improvements or optimization. Other key aspects of the growth mechanism, that is, roughness, morphology, and interdiffusion, are addressed. It is concluded that the requirements for the growth of non-c-axis heterostructures are more severe than those for the c-axis ones.

Magnetization processes in ultrathin Au∕Co∕Au films grown on a bifacial Mo(110)/Mo(540) single crystal

We studied magnetization reversal processes and magnetic anisotropy in ultrathin Au∕Co∕Au films deposited on a bifacial Mo(110)/(540) single crystal. The influence of the Co thickness and miscut angle on the spin reorientation from out-of-plane into in-plane magnetization were investigated by means of the magneto-optical Kerr effect (MOKE). In the case of Co grown on a vicinal Au∕Mo(540) substrate, the perpendicular magnetization component was found throughout the 1–8nm Co thickness range. The canted orientation of magnetization was deduced from vectorial MOKE magnetometry. The out-of-plane switching field, which is 160Oe for the perpendicular magnetization, increases to about 960Oe as observed at 8nm Co thickness on the vicinal part. The experimental data are discussed taking into account both uniaxial out-of-plane and in-plane magnetic anisotropy energy terms. The results indicate the possibility of tuning the perpendicular magnetization component with the use of vicinal substrates, and are important from both a surface physics and magnetic memory media point of view.

Formation of iron silicide nanodots on Si(1 1 1)– [formula omitted]Ag

Iron silicide dots of nanometer size were grown on Si(1 1 1)– 3 × 3 Ag substrates. Formation and magnetic properties of the dots have been investigated with scanning tunneling microscopy, low-energy electron diffraction, Auger electron spectroscopy and magnetic ex-situ measurements. Effect of passivating the Si substrate with Ag was discussed. The dots were found ferromagnetic and its composition was deduced to be ∼Fe 3Si. They nucleate preferentially at step edges than on terraces. Use of vicinal substrates thus enables fabricating arrays of the dots.

Strain relaxation in III–V semiconductor heterostructures

Strain relaxation in III–V semiconductor (0 0 1) epitaxial strained layers is considered with particular reference to the InGaAs/GaAS system. Possible mechanisms of relaxation are briefly reviewed. It is pointed out that relaxation is, and never can be, complete and that results relating to the extent of relaxation of thick layers, and the asymmetry of such relaxation in the two 〈1 1 0〉 should be interpreted with caution. Any asymmetry introduced by the use of vicinal substrates is less than the scatter among experimental measurements of relaxation.