The anisotropy in ZnO heteroepitaxial growth by CVD is studied on spherical and lens-shaped sapphire substrates. The layers of ZnO form maps containing many regions of single-crystals of various orientations. By combining equivalent types of these regions, six different modes in the orientation relationships between ZnO and sapphire are distinguished and classified. The effects of growth temperature and reaction gas velocity on the kinds and the extent of these regions are also investigated. The results, drawn by stereographic projection, may provide a useful guide for selecting and preparing substrate planes to obtain specific ZnO planes of high quality, i.e. smooth surface, high perfection, high electron mobility etc.

Chemically vapour deposited silicon on sapphire (SOS) films 0.25 μm thick were implanted with 28Si+ and recrystallized in solid phase by furnace annealing (FA) and IR rapid thermal annealing (RTA) in the laboratory. An improvement in crystalline quality can be obtained using both annealing procedures. After FA, it is hard to retain the intrinsic high resistivity value (104–105 Ω cm) observed in as-grown SOS films, so the improvement process cannot be put to practical use effectively. However, it is demonstrated that by properly adjusting the implantation and RTA conditions, significant improvements in both film quality and film autodoping can be accomplished. This work describes a modified double solid phase epitaxy process in which the intrinsic high resistivities of the as-grown SOS films are retained. The mechanism of suppression of Al autodoping is discussed.


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Micro-nano ZnO whiskers and dots have been selectively grown on sapphire substrate using Au/Pt catalyst arrays. The catalyst array was fabricated by employing a nanoindentation tester, which is simpler than conventional micro-nano fabrication techniques. The electric current heating (ECH) method was used to provide ZnO sources from a ZnO ceramic bar heated to about 1000 °C. The whiskers and dots were grown in the Vapor–Liquid–Solid (VLS) growth mode inside a gold image furnace. SEM images identified dramatic differences in the crystal structures grown at 940 °C, specifically, whiskers for Au catalyst and dots for Pt catalyst.

Whiskers are characterized by diameters of 10 nm to sub-micron and lengths from sub-microns to tens of microns. Dots, however, have a uniform diameter of about 100 nm. We found growth beginning at the arrayed Au catalyst positions. In contrast, dots were formed, but no whiskers were observed around the Pt catalyst. These features are explained in terms of different catalyst melting points: VLS growth was realized for the Au catalyst but not for the Pt catalyst at 940 °C. Good to excellent quality ZnO whisker and dot crystals was confirmed by micro-photoluminescence (PL) measurement.


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Sapphire (α-Al2O3) single crystals grown using the Verneuil and Kyropoulos methods have been analyzed using electron paramagnetic resonance and γ-ray spectroscopy with 12-MeV bremsstrahlung excitation. It is established that uncontrolled impurities in the final sapphire single crystals grown by the Kyropoulos method in molybdenum-tungsten crucibles are supplied both from the initial materials and from the furnace and crucible materials.

Transparent high optical quality and large Ti-sapphire (Ti3+-doped Al2O3) single crystals have been grown by the Kyropoulos technique (KT) for optical amplification. The present work shows that by the utilization of KT growth technology and the optimization of the growth conditions it is possible to grow Ti-doped Al2O3, 100 mm in diameter and 5 kg in weight. We have demonstrated that large Ti(0.25 atom %)-doped Al2O3 crystals show high chemical homogeneities and good optical properties and amplify the energy without any special annealing. Ti-doped sapphire crystals are for high power laser applications and particularly for the shortest pulses ever produced from a laser oscillator.


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This paper addresses the formation of freestanding GaN substrates by a natural separation mechanism, effectively eliminating the need for post-growth processes such as laser liftoff, chemical etching or mechanical lapping to form freestanding GaN substrates. A number of GaN thick films were grown onto sapphire substrates by the hydride vapor-phase epitaxy (HVPE) method with thickness varying from 200 μm to 3.8 mm using either a low-temperature GaN or an AlN buffer as the nucleation step. We have found that samples grown on a low temperature GaN buffer naturally delaminate from the sapphire substrate post-growth over the entire thickness range studied. Furthermore, we have observed that the thinner films have high crack densities leading to the delamination of several smaller freestanding pieces. As the GaN thickness increases, the area of the delaminated pieces also increases, ultimately leading to a 1-to-1 correlation between initial sapphire substrate area and freestanding GaN area. However, the GaN films grown on AlN buffers did not delaminate. These results were accounted for by calculating the thermal stresses in the GaN film and substrate as a function of film thickness using Stoney's equation and assuming that the GaN buffer undergoes decomposition at the growth temperature.

Catalytic growth of GaN nanowires by hydride vapour phase epitaxy is demonstrated. Nickel–gold was used as a catalyst. Nanowire growth was limited to areas patterned with catalyst. Characterization of the nanowires with transmission electron microscopy, x-ray diffraction, and low temperature photoluminescence shows that the nanowires are stoichiometric 2H-GaN single crystals growing in the orientation when grown on sapphire, with occasional stacking faults along the c-axis as the only defect type observed in most of the wires. A red shift observed in the photoluminescence was too large to be explained by the minor strain observed alone, and was only marginally affected by temperature, suggesting a superposition of several factors.


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