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On an SiO2-patterned sapphire substrate, polarity-inverted lateral overgrowth produced N- and Ga-polar GaN on the opening regions and on the SiO2 mask regions, respectively. Ga-polar GaN was found ...

The remote epitaxy was originally proposed to grow a film, which is not in contact but crystallographically aligned with a substrate and easily detachable due to a van der Waals material as a space layer. Here we show that the claimed remote epitaxy is more likely to be nonremote `thru-hole' epitaxy. On a substrate with thick and symmetrically incompatible van der Waals space layer or even with a three-dimensional amorphous oxide film in-between, we demonstratively grew GaN domains through thru-holes via connectedness-initiated epitaxial lateral overgrowth, not only readily detachable but also crystallographically aligned with a substrate. Our proposed nonremote thru-hole epitaxy, which is embarrassingly straightforward and undemanding, can provide wider applicability of the benefits known to be only available by the claimed remote epitaxy., 19 pages, 5 figures, Supplementary Information (26 pages, 15 figures)

During epitaxial lateral overgrowth, the lateral polarity inversion of c-GaN domains from Ga to N polarity, triggered at the boundary of an SiO2 mask pattern, resulted in inversion domain boundaries (IDBs) forming preferentially on the \{11{\overline 2}0\} plane, although the formation energy of IDBs on the \{1{\overline 1}00\} plane is known to be lower than that on the \{11{\overline 2}0\} plane. A model that takes a geometrical factor into consideration can explain this preferential tendency of IDB formation on the \{11{\overline 2}0\} plane, and computational simulations based on the proposed model are consistent with experimental results. In contrast with the vertically upright IDBs observed in N-to-Ga polarity inversion, vertically slanted IDBs were formed in some samples during the inversion from Ga to N polarity. These polarity inversions, which appeared to randomly occur on the mask pattern, turned out to be triggered at the mask pattern boundaries.

The polarity and threading dislocation dependence of the surface morphology of c-GaN films exposed to HCl vapor at temperatures of 750 and 810 °C was investigated. For N-polar GaN, some regions were severely etched in such a way that vertically-aligned nanopipes were formed while areas other than those occupied by the nanopipes were barely etched. A cross-sectional transmission electron microscopy analysis revealed that the bottom of the nanopipes was observed to be connected to threading dislocation(s) while no threading-dislocation was observed beneath the unetched surface of N-polar GaN. In comparison, the threading-dislocation-free region in Ga-polar GaN domains was heavily etched, and GaN nanoneedles were formed on a relatively flat surface at temperatures as low as 750 °C. In order to understand the etched surface morphology of Ga-polar GaN (nanoneedles on a relatively flat surface), we proposed a physical model to describe this etching behavior, and a computational simulation based on our proposed model could explain the etched surface morphology of a Ga-polar GaN film exposed to HCl vapor.

Heteroepitaxial growth of ({\overline 1}103)-oriented GaN domains on m-plane sapphire is energetically unfavourable in comparison with that of (1{\overline 1}0{\overline 3})-oriented GaN domains, but the faceted domains with ({\overline 1}103)-oriented GaN reveal a more m-facet-dominant configuration than (1{\overline 1}0{\overline 3})-oriented GaN in such a way that the quantum-confined Stark effect can be more effectively suppressed. It is reported here, for the first time, that semipolar ({\overline 1}103)-oriented and faceted GaN domains can be grown on an SiO2-patterned m-plane sapphire substrate by employing polarity inversion of initially nucleated (1{\overline 1}0{\overline 3})-oriented GaN domains. This polarity inversion of semipolar GaN was found to occur when the domains were grown with a 20–37.5 times higher V/III ratio and 70 K lower growth temperature than corresponding parameters for polarity-not-inverted domains. This work opens up a new possibility of effective suppression of the quantum-confined Stark effect by polarity-controlled semipolar GaN in an inexpensive manner in comparison with homoepitaxial growth of ({\overline 1}103)-oriented GaN on a GaN substrate.

Si supply mechanism in the spontaneous formation of SiO 2 pattern on a Cu foil, which was previously reported to enable the selective growth of graphene in no direct contact with organic materials, was investigated. Upon annealing at 1000 °C and atmospheric pressure, SiO 2 in the Fe-coated SiO 2 /Al 2 O 3 template covered by a Cu foil was found to be severely decomposed by Fe droplets. No signature of reaction between SiO 2 and Fe droplets suggested that Si species, which contributed to the spontaneous formation of SiO 2 pattern on a Cu foil, originated from SiO 2 catalytically decomposed by Fe droplets. In the absence of a Cu foil covering an Fe-coated SiO 2 /Al 2 O 3 template, the catalytic activity of Fe droplets was significantly suppressed because of the encapsulation of Fe droplets by a 2-nm-thin-Fe 3 O 4 layer. Furthermore, a part of the Fe film on SiO 2 /Al 2 O 3 without a Cu foil turned into nanodroplets and assisted the formation of SiO 2 nanowires. These results reveal that a Cu foil made an intriguing role in preventing Fe from being encapsulated by Fe 3 O 4 , so the catalytic role of Fe droplets was not terminated until SiO 2 was fully decomposed. Our experimental results provided insights into better understanding of these intriguing behaviors of Fe and Cu on SiO 2 at high temperature and at atmospheric pressure.

Randomly formed close-packed arrays of 3-μm-large polystyrene microspheres on a sapphire substrate by drop-casting were found to convert to two-dimensional non-close-packed ones when the microsphere-coated substrate was dipped into and taken out of a chloroform/ethanol mixed solution with specific volume fractions. The conversion was found to be associated with (1) the increased center-to-center distance between nearest neighboring microspheres caused by the increase in size and (2) the subsequently increased edge-to-edge distance between them caused by the decrease in size with their positions not much changed. The increase of microspheres in size was due to swelling by absorbing chloroform. The subsequent decrease of microspheres in size was due to deswelling caused by gradual change in the solvent environment during evaporation. The dependence of conversion from closed-packed arrays to non-close-packed ones on the volume fraction of each constituent was investigated. This type of conversion was found to occur readily on both sapphire and Si substrates.

When a 25-μm-thick Cu foil placed on top of a selectively FeCl3-coated quartz substrate was heated inside a furnace at 1000 °C in a H2/Ar atmosphere, a FeCl3 mask pattern on a quartz was spontaneously transferred to the front side of the Cu foil. Due to this spontaneous pattern transfer, a subsequent heating process in H2/Ar/CH4 atmosphere led to selective growth of graphene on the front side of the Cu foil. Surface analysis revealed that a spontaneously transferred mask on a Cu foil was made of SiO2, and Si in SiO2 was found to be from the quartz substrate. Computational simulation of surface diffusion of Si on a Cu foil was consistent with experimentally observed microstructures of spontaneously transferred pattern boundaries, which suggests that oxidation of diffused Si atoms, which originated from the FeCl3-coated region of a quartz, on the Cu surface was the crucial mechanism of the spontaneous pattern transfer.

The mechanism of preferential nucleation of [1{\overline 1}0{\overline 3}]-oriented GaN faceted twins on an SiO2-patternedm-plane sapphire substrate was investigated. Each variant of twins, which were enclosed byc- andm-facets, was observed to be preferentially nucleated over the opposite sides of an SiO2pattern. It was hypothesized, from the fact that the same method of Legendre transformation is applied to a Wulff plot and a kinetic Wulff plot to determine the growth morphology of a crystalline domain, that theeffectivesurface energy ofc- andm-facets would be proportional to the growth rate of the respective facet. On the basis of this hypothesis, minimization of the effective surface energy of a nucleated domain was proposed as a mechanism of preferential nucleation. This proposed mechanism successfully explained the preferential nucleation behaviour.

On an SiO2-patterned c-plane sapphire substrate, GaN domains were grown with their polarity controlled in accordance with the pattern. While N-polar GaN was grown on hexagonally arranged circular openings, Ga-polar GaN was laterally overgrown on mask regions due to polarity inversion occurring at the boundary of the circular openings. After etching of N-polar GaN on the circular openings by H3PO4, this template was coated with 40-nm Si by sputtering and was slightly etched by KOH. After slight etching, a thin layer of Si left on the circular openings of sapphire,but not on GaN, was oxidized during thermal annealing and served as a dielectric mask during subsequent regrowth. Thus, the subsequent growth of GaN was made only on the existing Ga-polar GaN domains, not on the circular openings of the sapphire substrate. Transmission electron microscopy analysis revealed no sign of threading dislocations in this film. This approach may help fabricating an unholed and merged GaN film physically attached to but epitaxially separated from the SiO2-patterned sapphire.

Selective thermal diffusion of Cu into a 100-nm-thick SiO2-patterned Si(001) substrate was investigated to elucidate the spontaneous formation of Cu-Si alloy nanoparticles. Transmission electron microscopy and energy dispersive X-ray spectroscopy provided the indirect evidence for the formation on the substrate’s surface of nanoparticles that served as a catalyst to grow SiO2 nanowires selectively in window regions. The microstructural analysis revealed that thermal annealing caused selective diffusion of Cu into the Si matrix in window regions only and that the Cu-Si alloy nanoparticles were formed at 900 °C although the diffusion of Cu into Si was already significant at 700 °C. The nanoparticles that were sparsely distributed below the surface of the Si matrix did not serve as a catalyst for growing SiO2 nanowires, and the chemical composition analysis showed that the nanoparticles at the tip of SiO2 nanowires were Cu3Si.

Spontaneously regulated in-plane polarity inversion ofa-oriented GaN domains has been demonstrated for the first time. Crystallographic analysis revealed that each domain grown on circular-hole-patternedr-plane sapphire substrates has basal faces with oppositely oriented in-plane polarity. The inverted orientation of in-plane polarity on the opposite basal faces is not due to merging between in-plane polarity-inverted domains nucleated on the patternedr-plane sapphire substrate, but it was found to be due to spontaneous formation of an inversion domain boundary on the growth fronts of existing domains. This result provides new insights into controlling the in-plane polarity ofa-oriented GaN, because the nucleation of in-plane polarity-inverted domains ofa-oriented GaN onr-plane sapphire is symmetrically not allowed.

Regularly branched InN nanostructures were controllably grown onc-plane sapphire substrates by using hydride vapor phase epitaxy. On the basis of the crystallographic analysis of these InN tetrapods, it is proposed that (i) each tetrapod consists of four nanorods in the wurtzite phase protruding from a truncated tetrahedral nanocore in the zinc-blende phase and that (ii) branching occurs at the four {111} faces of the truncated tetrahedral nanocore. Our work suggests that the branching regularity of InN tetrapods is attributed to the polytypic transition at these four faces.

Effective surface energy is proposed to analyze the morphological evolution of crystalline domains in nonequilibrium shape. This concept can be used to determine how favorable the formation of a certain crystallographic face is when a crystalline domain is grown even in kinetically limited conditions by incorporating various kinetic effects on the corresponding crystallographic face into the actual surface energy of that face. In this work, it is experimentally demonstrated that this concept, applied to the m-oriented GaN faceted domains grown under kinetically limited conditions on SiO2-patterned m-plane sapphire substrates, can successfully describe the morphological evolution of those GaN faceted domains in nonequilibrium shape. This method can give a new insight into the morphological analysis of crystalline domains in nonequilibrium shape.

Many characteristics of epitaxially grown films depend sensitively on their orientations. In most cases, orientation is uniquely determined by that of the substrate, a correlation established by energy minimization. Here, we show that substrate-independent control of orientation is possible by paths available in kinetically limited growth regimes for materials exhibiting polytypism. Demonstrated for GaN, our intriguing results provide fundamentally new insight into controlling one of the most important structural parameters of epitaxial films. This approach might be readily extended to other III-nitrides and ZnO, which also exhibit polytypism. Our procedures can be easily applied to tailor characteristics of epitaxial films, allowing investigations of new properties such as unipolarity.

The crystallographic and structural characteristics of GaN tripods and hexapods grown onc-plane sapphire substrates were investigated using synchrotron X-ray scattering and microscopic analysis. The core structure of a GaN hexapod is revealed to be in the zincblende phase with an inversion domain, and a refined crystallographic analysis of tripods and hexapods with synchrotron X-ray scattering shows the existence of the zincblende phase in wurtzite-based protruding nanorods. The atomistic model combined with this crystallographic analysis reveals that the core size of a hexapod is much smaller than the diameters of the protruding nanorods. This refined structural analysis can be utilized in tailoring the opto-electronic characteristics of GaN multipods.

GaN nanorods were grown on Si(1 1 1) substrates by using hydride vapor phase epitaxy, and the crystallographic characteristics associated with their preferred growth directions were investigated by utilizing synchrotron X-ray reciprocal space mapping in a grazing incidence geometry and scanning electron microscopy. Crystallographic analysis reveals that the nanorods containing both wurtzite and zinc blende phase tend to have narrower distribution of the preferred growth directions than those containing only wurtzite phase. This tendency is partly attributed to the subtle interplay between polytypism and the preferred growth directions of GaN nanorods.

A c -oriented GaN film was grown on a r -plane sapphire substrate by utilizing hydride vapor phase epitaxy. This non-typical orientational relation between the film and the substrate was possible by spontaneous transition in preferred orientation, and voids were spontaneously formed in an orientation-transition layer. This c -oriented thick GaN film was then self-separated from the substrate during cool-down process to room temperature after the growth. This intriguing phenomenon of the self-separation of crack- and strain-free GaN is attributed to the spontaneous formation of voids during the preferred orientation-transition, and suggests a novel method to fabricate crack- and strain-free GaN free-standing templates.

GaN nanorods were grown on c-plane sapphire substrates by using catalyst-free hydride vapor phase epitaxy (HVPE). The effects of substrate temperature, Ga boat temperature, and Ga pretreatment on the surface morphology of GaN nanorods were investigated. From the dependence of a radial and axial growth rate on the substrate temperature, the kinetically limited process was found to be a rate determining step in the growth of GaN nanorods in HVPE. In addition, the activation energy of the growth along the both axial and radial directions were estimated. The dependence of a Ga boat temperature and the Ga pretreatment effect revealed that the density of nanorods were dependent on the flux of Ga species on the substrate.

GaN films were grown on c -plane sapphire substrates by using hydride vapor phase epitaxy (HVPE) with a pulsed flow of HCl over Ga metal. NH 3 gas supply was controlled to flow in a constant rate or in a modulated way. The surface morphology dependence of these films on the various flow modulation schemes was investigated. Depending on the duty cycle of NH 3 flow, the surface morphology of GaN films was sensitively modified. This sensitive response of surface morphology of GaN films to the flow modulation was attributed to diffusion efficiency variation of Ga species under different gas environment. Under proper modulation conditions, flattened top-surface morphology of nucleated domains was found to be obtained.

The role of a NH4Cl layer grown between GaN and a sapphire substrate for self-separation of GaN films was investigated in detail. Microstructural analysis of the NH4Cl layer reveals that self-separation of a GaN film was effectively assisted by the sub-micrometer-sized voids formed due to etching of GaN by evaporated NH4Cl. An areal fraction of nonetched GaN in contact with sapphire substrate was found to be linearly dependent on the thickness of NH4Cl layer and to have two different proportionality constants below and above an NH4Cl thickness at which GaN begins to be self-separated. This intriguing behavior was well explained by a simple model that takes account of void merging.

GaN nanodisks, which can be used as nanoscale dielectric resonators for compact photonic nanodevices, were grown by using hydride vapor-phase epitaxy with growth interruption. Growth interruption enhanced surface migration of species and controlled growth interruption allowed the formation of GaN nanodisks at a growth temperature of 1050 C and even at a growth temperature as low as 510 C.

GaN nano-grains were grown on nominally 0.3°-miscut (0 0 0 1) sapphire substrates by hydride vapor phase epitaxy (HVPE). Ordering behavior of the nano-grains was investigated by utilizing scanning electron microscopy (SEM) and synchrotron X-ray scattering. SEM images and synchrotron X-ray scattering measurement revealed that the nano-grains were nucleated with long-range ordering along the sapphire [ 1 0 1 ¯ 0 ] , which is the same as the miscut direction. With an increased growth time the nano-grains gradually coalesced, but the long-range ordering was still observed even after completion of the coalescence.

InN nanograins were directly grown on -miscut (toward M-plane) c-plane sapphire substrates by hydride vapor phase epitaxy (HVPE) and their growth characteristics were investigated by utilizing x-ray scattering. Depending on the various growth parameters, the formation of InN was sensitively influenced. Six samples were grown by changing HCl flow rate, the substrate temperature and Ga/In source zone temperature. All the samples were grown on unintentionally sapphire substrates. By increasing the flow rate of HCl from 10 sccm to 20 sccm, the formation of GaN grains with different orientations was observed. On the other hand, when the substrate temperature was raised from to , the increased substrate temperature dramatically suppressed the formation of InN. A similar behavior was observed for the samples grown with different source zone temperatures. By decreasing the source zone temperature from to , a similar behavior was observed.

Surface X-ray scattering and scanning–tunneling microscopy experiments, performed in situ, are used to investigate the influence of quantum size effects on the growth of Pb on the Si(111)7×7 surface. It is demonstrated that the structure of Pb islands and the associated wetting layer are consistent with the effects of quantum confinement. Moreover, these effects lead to novel behavior for the coarsening evolution of the Pb islands. For example, Ostwald ripening is not observed due to a breakdown of the classical Gibbs–Thomson effect. An unanticipated strong dependence on the deposition flux rate is found and we measure island decay times that are orders of magnitude faster than predicted. These results have important implications for understanding and controlling the growth of nanostructures.

Epitaxial lateral overgrowth in tandem with the first-principles calculation was employed to investigate the determining factor of a preferred orientation of GaN on SiO2-patterned m-plane sapphire substrates. We found that the (1"Equation missing"00)-orientation is favored over the (1"Equation missing"0"Equation missing")-orientation in the region with a small filling factor of SiO2, while the latter orientation becomes preferred in the region with a large filling factor. This result suggests that the effective concentration determines the preferred orientation of GaN: the (1"Equation missing"00)- and (1"Equation missing"0"Equation missing")-orientations preferred at their low and high concentrations, respectively. Our computational study revealed that at a low coverage of Ga and N atoms, the local atomic arrangement resembles that on the (1"Equation missing"0"Equation missing") surface, although the (1"Equation missing"00) surface is more stable at their full coverage. Such a (1"Equation missing"0"Equation missing")-like atomic configuration crosses over to the local structure resembling that on the (1"Equation missing"00) surface as the coverage increases. Based on results, we determined that high effective concentration of Ga and N sources expedites the growth of the (1"Equation missing"0"Equation missing")-orientation while keeping from transition to the (1"Equation missing"00)-orientation. At low effective concentration, on the other hand, there is a sufficient time for the added Ga and N sources to rearrange the initial (1"Equation missing"0"Equation missing")-like orientation to form the (1"Equation missing"00)-orientation.

E-mail: ckim@khu.ac.krReceived October 14, 2011, Accepted January 9, 2012Key Words : Gallium nitride, Amplified spontaneous emission, Superlinear increase, Wide band gapSemiconductor nanowires have been the subject of intensestudy in recent years. In particular, their ability to confineelectrons/holes and photons makes them attractive aspotential building blocks of nanoscale electronics and opto-electronic devices.

We have investigated the electrical properties and interfacial reactions of the Si/Ti-based ohmic contacts to Si-doped n-GaN grown by metal organic chemical vapor deposition and the electrical properties were related to the material reactions. Si/Ti contact system was selected because Ti silicides have a low work function comparable to Al and also Si was used widely as an n-type dopant. As the annealing temperature increased, the specific contact resistance of Si/Ti-based ohmic contacts decreased and showed minimum contact decreased and showed minimum contact resistance as low as 3.86 10−6 cm2 after annealing at 900°C for 3 min under N2 ambient. Our experimental results show that the ohmic behavior of Si/Ti-based contact, were attributed to the low barrier height of Ti-silicide/GaN interface, which was formed through the interfacial reaction between Si and Ti layers. In order to clarify the current conduction mechanism of Si/Ti-based contact, temperature dependent contact resistance measurement was carried out for Au(1000 A)/Ti(400 A)/Si(1500 A)/Ti(150 A) contact system after annealing at 700°C for 3 min. The contact resistance of Si/Ti-based ohmic contact decreased exponentially with the measuring temperature and so it can be concluded that current flows over the low barrier height by thermionic emission.

We report a novel structure of a selectively grown buried-ridge (SGBR) type nitride-based laser diode structure grown on sapphire and lateral epitaxial overgrowth (LEO) substrates by metal-organic chemical vapor deposition (MOCVD). The AlGaN layers were designed for current confinement into ridge as well as to enhance lateral optical confinement by introducing an index difference between MQW and AlGaN layers in the lateral direction. The I–V characteristics of SGBR structure on LEO substrate showed no leakage current upto a reverse bias of −10 V. From an EL image through transparent metal, we demonstrated that the current path was well defined into the ridge region.

Heteroepitaxial GaN film was grown on sapphire (0 0 0 1) substrate by hydride vapor-phase epitaxy and it was observed employing scanning electron microscopy and cathodoluminescence that there were microstructural inhomogeneous areas showing suppressed luminescence characteristics compared with the surrounding matrix. They were presumed to be induced by polarity-inverted domains identified on the basis of the chemical inertness and heavily doped characteristics manifested in cathodoluminescence spectra.

Effect of etched sapphire substrates on the nucleation characteristics of GaN nanorods was investigated. c-plane sapphire substrates (0.3°-miscut toward m-plane (1 010) were etched in situ by HC1 at 1015 °C in the reactor of hydride vapor phase epitaxy (HVPE). GaN nanorods were grown on these etched sapphire substrates by using HVPE. Etched sapphire substrates had many step structures with different heights. Most of GaN nanorods were grown on the step regions and rarely observed on the terrace regions. The preferred nucleation positions were, however, found to extend to terrace regions if the growth temperature was increased.

X-ray diffraction has been employed to investigate the strain relaxation of both components of a GaN/AlN bilayer on sapphire (0001) as a function of the GaN layer thickness. Below a critical thickness, GaN and AlN both relax with the same in-plane lattice constant, consistent with the energy minimum condition of elasticity theory for a bilayer. Above the critical thickness, however, the strain relaxations in the two layers were different. We can fit this strain relaxation behavior with a free standing bilayer model with an additional term describing the interaction of dislocations.

GaN nanograins were grown on a c-plane sapphire substrate and their strain relaxation due to x-ray irradiation was investigated in-situ by utilizing synchrotron xray scattering. The GaN nanograins were constantly exposed to the synchrotron X-ray and θ -2θ scans through the (002) Bragg peak of GaN were repeatedly carried out during the irradiation. The Bragg peak of the compressively strained GaN nanograins gradually shifted toward higher angle, which implies that the GaN nanograins in compressive strain experienced strain relaxation during x-ray irradiation. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A strained pseudomorphic Si0.7Ge0.3 film grown by gas-source molecular-beam epitaxy on Si(001) was irradiated at room temperature with 25 keV Ga+ ions. The gradual strain relaxation of the metastable Si0.7Ge0.3 film was monitored using in situ x-ray diffraction as a function of dose. Based on a dimensional argument, the ion-induced damage scales as extended defects. The Hendricks-Teller model was successfully applied to explain the shifting and broadening of the additional diffuse scattering.

p-type GaN films were grown at two different temperatures, 650 and 700°C, by plasma-assisted molecular beam epitaxy (PAMBE) using a radio frequency (RF) plasma source. High hole concentrations of the order of 10 18 cm −3 were achieved for both films without any post-growth treatment. For (0 0 0 2) diffraction from the p-type films grown at 700°C, the full-width at half-maximum (FWHM) of the double-crystal X-ray rocking curve was 7.8 arcmin, the smallest ever reported for p-type GaN films grown on sapphire substrates. The room-temperature photoluminescence (PL) measurements on both films showed that band edge emission at 365 nm dominated the PL spectra of the films grown at 700°C, while emission at 413 nm, associated with deep Mg complexes, dominated those of the films grown at 650°C. The films grown at 700°C showed better crystalline quality and optical properties than those grown at 650°C.

Refined structure of (√3 × √3) surface reconstruction induced by Sb adsorbed on Si(111) was obtained from X-ray diffraction, using a Patterson function and a least-squares fit. A wide range of reciprocal space was probed to get information for the lateral and the vertical displacements of adsorbate and the top layers of Si. The Patterson function confirms the “milk stool” trimer model, which, according to a least-squares fit, is centered on the T 4 site. The thermal vibration amplitudes of Sb ad-atoms and those of surface layers of Si were obtained and comparison with the values in other surfaces are made.

We present the results of in situ x-ray scattering experiments that investigate the growth of Pb nanocrystalline islands on Si(111). It is conclusively shown that the Pb nanocrystals do not reside on top of a Pb wetting layer. The nucleating Pb nanocrystals transform the highly disordered Pb wetting layer beneath the islands into well-ordered fcc Pb. The surface then consists of fcc Pb islands directly on top of the Si surface with the disordered wetting layer occupying the region between the islands. As the Pb nanocrystals coalesce at higher coverage we observe increasing disorder that is consistent with misfit strain relaxation. These results have important implications for predicting stable Pb island heights.

The analysis of x-ray diffuse scattering measurements on Ag homoepitaxial films is presented. The experiments, which establish that a low concentration of large vacancy clusters can be incorporated into noble metals during homoepitaxial growth, were performed on 100 monolayer films of Ag deposited on Ag(001) at low temperature. The diffuse scattering of this film was measured, in situ, near several in-plane Bragg positions in grazing-incidence geometry. Because of the large dilatation from the vacancy clusters, the usual approximations of Huang and Stokes-Wilson scattering cannot be made and it is shown that numerical integration of the diffuse scattering equations leads to good agreement between the data and a point-defect scattering model.

A highly disordered GaN nanostructure was grown by using hydride vapor phase epitaxy on an Si(100) substrate, and its diffuse reflectivity was measured in the 200–1200 nm spectral range by using an integrating sphere. A modified multiple-scattering-based model successfully explained the spectral distribution of diffuse reflectivity of this highly disordered GaN nanostructure.

MgO thin films were epitaxially grown on Al2O3(0001) substrates using metalorganic chemical vapor deposition. For film growth, bis-cyclopentadienyl-Mg and oxygen were employed as reactants. X-ray diffraction (XRD) θ–2θ scan and θ-rocking curve data showed a preferred film orientation of [111] direction along Al2O3[0001]. The XRD rocking curve of films grown at 600°C showed a full width at half maximum as narrow as 0.45°, indicating good crystallinity. The pole figures of MgO thin films, which show clearly six poles with 60° of rotational symmetry, imply that the MgO films were epitaxially grown with either 60° twins or inversion domains. Based on the pole figure and azimuthal scan measurements, the epitaxial relationship of MgO(111)//Al2O3(0001) and MgO[10]//Al2O3[100] was determined. More importantly, the vertical alignment and surface morphology of the thin films were significantly improved by doping Zn during MgO film growth.

At various doping concentrations of Si in GaN films, the correlation between the type of dislocations and photoluminescence (PL) characteristics was investigated. A different broadening behavior of symmetric and asymmetric Bragg peaks as a function of carrier concentration provided qualitative evidence that the type of threading dislocations generated in GaN layers was strongly dependent on the doping levels of Si. PL spectra in conjunction with x-ray rocking curve measurements suggested that the yellow luminescence associated with deep levels was more strongly related with edge dislocations than screw or mixed ones.

Large-sized and high-quality free standing GaN are required with the development of GaN-based devices. We have developed new techniques to reduce the price of GaN substrates. In this paper, we introduce a simple fabrication way of freestanding GaN substrate using hydride vapor phase epitaxy (HVPE). An evaporable buffer layer was applied for the fabrication of 2inch freestanding GaN to separate from a sapphire substrate, in other words, a freestanding GaN was fabricated only by HVPE (one-stop process) without any process.