Lateral Growth Region Research Articles

Study of lateral growth regions in ammonothermal c-plane GaN

Lateral growth in the a-direction is an effective way to expand the size of crystal in basic ammonothermal GaN growth. Cathodoluminescence image of cross section clearly revealed several different regions along a-direction. Stress distributions and optical properties were investigated among these different regions by Raman spectroscopy and photoluminescence spectroscopy, respectively. TOF-SIMS mapping showed the spatial distribution of O, H, Si and C impurities in lateral growth regions. Our results indicate that there is small stress variation among the interfaces. Different concentration of impurities incorporated in these regions, especially O impurity, which can significantly increase the free carrier concentration. Fairly low concentration and uniform distribution of C impurity indicated that YL band in PL spectra is not closely related to carbon impurity or a complex involving carbon. Based on the above data, the evolution process of lateral crystal growth is deduced.

Homoepitaxy Growth of Single Crystal Diamond under 300 torr Pressure in the MPCVD System.

The high-quality single crystal diamond (SCD) grown in the Microwave Plasma Chemical Vapor Deposition (MPCVD) system was studied. The CVD deposition reaction occurred in a 300 torr high pressure environment on a (100) plane High Pressure High Temperature (HPHT) diamond type II a substrate. The relationships among the chamber pressure, substrate surface temperature, and system microwave power were investigated. The surface morphology evolution with a series of different concentrations of the gas mixture was observed. It was found that a single lateral crystal growth occurred on the substrate edge and a systemic step flow rotation from the [100] to the [110] orientation was exhibited on the surface. The Raman spectroscopy and High Resolution X-Ray Diffractometry (HRXRD) prove that the homoepitaxy part from the original HPHT substrate shows a higher quality than the lateral growth region. A crystal lattice visual structural analysis was applied to describe the step flow rotation that originated from the temperature driven concentration difference of the C2H2 ion charged particles on the SCD center and edge.

Dendrite growth and defects formation with increasing withdrawal rates in the rejoined platforms of Ni-based single crystal superalloys

The effect of withdrawal rates on the dendrite growth and defects formation in the rejoined platforms of a Ni-based single crystal superalloy during directional solidification was studied by experimental investigations and ProCAST simulations. The results showed that the dendrite pattern in the rejoined platforms mainly comprised two regions: original primary dendrite region and lateral growth region. With increasing withdrawal rate, the lateral growth was more severe and the tendency of low angle grain boundaries (LABs) was greater because of dendrite deformation. Once the withdrawal rate exceeded 100 μm/s, local fragmentation appeared in the middle of the platforms and some ternary dendrites were detached from their parent dendrites. When the withdrawal rate was increased to 150 μm/s, lots of dendrite fragments formed and the integrity of single crystal was completely destroyed, which might be caused by the solute enrichment and was further promoted by the unstable growth conditions.

Spatial distribution of crystalline quality in N-type GaN grown on patterned sapphire substrate

The epitaxial layers of n-type GaN were grown on both planar and patterned sapphire substrate (PSS) by metal organic chemical vapor deposition. By comparing the epitaxial layers grown on planar substrate, GaN grown on PSS exhibited many improvements both on surface morphology and crystalline quality according to the characterization of atoms force microscopy, and high resolution X-ray diffraction. Spatially resolved micro-Raman scattering results were performed for mapping the spatial variations in crystalline quality of the n-type GaN grown on PSS. According to the variations on the intensity and the full width at half maximum of GaN E2 (high) peaks, the crystalline quality improvement occurred in the lateral growth regions which correspond to center region of the pyramid patterns. We proposed that the bending of dislocations during the lateral growth plays an important role in the spatial variations of GaN crystalline quality. Cross sectional transmission electron microscope and spatial cathodoluminescence mapping results further supported the explanation of the dislocation inhibition during the growth process of GaN grown on PSS.

Void Structures in Regularly Patterned ZnO Nanorods Grown with the Hydrothermal Method

The void structures and related optical properties after thermal annealing with ambient oxygen in regularly patterned ZnO nanrorod (NR) arrays grown with the hydrothermal method are studied. In increasing the thermal annealing temperature, void distribution starts from the bottom and extends to the top of an NR in the vertical (c‐axis) growth region. When the annealing temperature is higher than 400°C, void distribution spreads into the lateral (m‐axis) growth region. Photoluminescence measurement shows that the ZnO band‐edge emission, in contrast to defect emission in the yellow‐red range, is the strongest under the n‐ZnO NR process conditions of 0.003 M in Ga‐doping concentration and 300°C in thermal annealing temperature with ambient oxygen. Energy dispersive X‐ray spectroscopy data indicate that the concentration of hydroxyl groups in the vertical growth region is significantly higher than that in the lateral growth region. During thermal annealing, hydroxyl groups are desorbed from the NR leaving anion vacancies for reacting with cation vacancies to form voids.

High-Hole-Mobility Single-Crystalline Ge Thin Films Formed on Insulating Substrates by SiGe Mixing-Triggered Directional Melting Growth

The development of high-carrier-mobility Ge-channel thin-film transistors (TFTs) is desired to realize advanced system-in-displays. To achieve the development of single-crystalline Ge films on insulating substrates, we have developed the directional melting growth process of amorphous Ge by using polycrystalline Si islands as growth seeds. Defect-free single-crystalline Ge stripes of 400 µm length are realized, and high-hole-mobilities of more than 1000 cm2 V-1 s-1 are demonstrated in the entire lateral growth region. This method opens up the possibility of fabricating high-speed Ge-channel TFTs for system-in-displays.

Effects of Lens Shape on GaN Grown on Microlens Patterned Sapphire Substrates by Metallorganic Chemical Vapor Deposition

The epitaxial growth of GaN on patterned -plane sapphire substrates having microlenses with a flat top, a dull tip, or a sharp tip is carried out. The growth mode, dislocation density, residual strain, and optical properties of GaN are investigated and correlated with the shape of the microlens. Because the growth of GaN does not take place on top of the microlens with a sharp tip, this type of patterned substrate leads to a wider low dislocation density lateral growth region, while it also gives rise to a higher compressive residual strain in GaN. For GaN grown on the microlens with a dull tip, many dislocations appear, resulting from the extra facets on the lens. It, however, has the lowest compressive strain among the samples studied. This work provides a guideline for preparing microlens patterned sapphire substrates for potential applications in high brightness InGaN light emitting diodes as both dislocation density and strain influence their internal quantum efficiency.

High rate photoelectrochemical etching of GaN and the use of patterned substrates for HVPE regrowth

High etching rates of HVPE GaN, up to 2 μm/min, have been achieved by photoelectrochemical etching to produce stripes which are 70–100 μm high. These wafers have been used as substrates for subsequent HVPE growth. The surface after the second growth was irregular and needed to be polished prior to defect density evaluation. The dislocation densities measured by the defect-selective etching were 2×10 7 cm −2 and 3×10 5 cm −2 in the stripe region and the low-dislocation-density lateral growth region, respectively. The low-dislocation-density regions formed stripes of about 10 μm.

Facet formation and lateral overgrowth of selective Ge epitaxy on SiO2-patterned Si(001) substrates

Faceting and lateral overgrowth have been investigated for Ge selectively grown on Si(001) substrates in trench regions bound by SiO2 sidewalls. In wet-etched large trenches with sloped sidewalls, Ge faceting behavior was similar to Si and SixGe1−x faceting: slow-growing {113} facets dominate, with {111} facets expanding as the layer became thicker. However, the {111} facet length for Ge was much smaller than that of Si; this can be explained in terms of mass transport and accumulation, as well as energy minimization and the higher surface diffusivity of Ge. In dry-etched small trenches with vertical sidewalls, minimization of the high-energy interface area between Ge and SiO2 appears to be most critical in determining faceting morphology. Overgrowth of Ge led to void formation at the oxide interface, presumably to avoid the high-energy Ge/SiO2 interface. Upon coalescence of lateral-growth regions, fast-growing (001) forms and dominates subsequent growth. Thus, the total thickness of the overgrown Ge layer was closely related to the width of the SiO2 region between trenches.

Dislocation generation at the coalescence of aluminum nitride lateral epitaxy on shallow-grooved sapphire substrates

The joining of defect-free AlN stripes is observed to trigger the generation of a large density of threading dislocations in the vicinity of the coalescence point. The AlN structure was grown by pulsed lateral epitaxy on shallow-grooved sapphire substrates. In the precoalescence stage, the dislocation density in the lateral epitaxial region (<108cm−2) is over two orders of magnitude less than in standard c-plane epitaxy. Basal-plane dislocations (b=a=13<112¯0>) are generated at the coalescence point as a result of relaxation of compressive stress that develops due to temperature gradients during growth. They bend toward the surface during the postcoalescence growth stage, leading to a high density of pure-edge threading dislocations in the lateral growth regions. Some threading dislocations form loops on prismatic planes in the crystal and the basal segments are observed to glide in the [0001] direction under the electron beam in the microscope.

Large Polycrystalline Silicon Grains Prepared by Excimer Laser Crystallization of Sputtered Amorphous Silicon Film with Process Temperature at 100 °C

Large polycrystalline silicon (poly-Si) grains with a diameter of 1.8 µm are successfully prepared by excimer laser crystallization (ELC) of a sputtered amorphous silicon (α-Si) film at a maximum process temperature of 100 °C. By pulsed DC magnetron sputtering, α-Si is deposited on a non-structured oxidized wafer. It is found that the α-Si film deposited with a bias is easily ablated during ELC, even at an energy density below the super lateral growth (SLG) region. However, the α-Si film deposited without a bias can endure an energy density well beyond the SLG region without ablation. This zero-bias sputtered α-Si film with a high compressive stress has a low Ar content and a high density, which is beneficial for the suppression of ablation. Large grains with a petal-like shape can be obtained in a wide energy density window, which can be a result from some fine crystallites in the α-Si matrix. These large grains with a low process temperature are promising for the direct formation of system circuits as well as a high-quality display on a plastic foil.

Au-induced lateral crystallization of a-Si 1− xGe x ( x: 0–1) at low temperature

Au-induced lateral crystallization of amorphous Si 1− x Ge x ( x: 0–1) on SiO 2 at a low temperature (400 °C) has been investigated. Although the growth velocity decreased with increasing Ge fraction, growth velocity exceeding 20 μm/h was obtained for all Ge fractions. As a result, poly-Si 1− x Ge x with large areas (> 20 μm) was obtained at a low temperature (400 °C). This is a great advantage of Au-induced lateral crystallization compared with Ni. However, the concentrations in the surface regions (depth: 0–20 nm) of the lateral growth regions were high (10–30%), though those in the deeper regions (depth: 20–50 nm) were as small as 1–2%. Removing of the surface regions with the high Au concentrations and gettering of Au atoms in the deeper regions are necessary to apply the grown layers to the device fabrication.

Lateral epitaxial patterned sapphire InGaN/GaN MQW LEDs

GaN epitaxial layers and InGaN/GaN multiquantum well blue light emitting diodes (LEDs) were prepared on both patterned sapphire substrates (PSS) and conventional sapphire substrates. From scanning electron microscopy micrographs of GaN epitaxial layers on PSS, it was found that lateral growth indeed occurred and the lateral to vertical growth rate ratio was around 2. It was also found that we could enhance the LED output power by using lateral epitaxial patterned sapphire. Such an enhancement could be attributed to the reduced dislocation density in the lateral growth regions of the epitaxial layers.

Homoepitaxial mesa structures on 4H–SiC (0 0 0 1) and [formula omitted] substrates by chemical vapor deposition

Selective epitaxial mesas of SiC were successfully grown on masked 4H–SiC (0 0 0 1) and (1 1 2 ̄ 0) substrates using a carbon mask by a CVD method. The carbon mask was removed by thermal oxidation without surface degradation, resulting in the successful formation of SiC epitaxial mesa structures on SiC substrates. The influences of crystal orientation, “step-flow growth” on SiC mesas, and polytypes of grown layers have been investigated. The external lateral growth on the carbon mask was observed along the 〈 1 1 2 ̄ 0 〉 direction on the off-axis (0 0 0 1) and along the 〈0 0 0 1〉 direction on the on-axis (1 1 2 ̄ 0) 4H–SiC substrates. Both on the off-axis (0 0 0 1) and the on-axis (1 1 2 ̄ 0) substrates, the main portion of epitaxial mesas is homoepitaxially grown 4H–SiC. Cross-sectional transmission electron microscopic analysis revealed that 3C–SiC existed at the upstream side of step-flow on the off-axis (0 0 0 1) substrate and in the external lateral growth region along the 〈0 0 0 1〉 direction on the on-axis (1 1 2 ̄ 0) substrate.

Interference microscopy for nanometric surface microstructure analysis in excimer laser processing of silicon for flat panel displays

The rapid control of laser crystallisation during in-line large area flat panel display fabrication using polysilicon (poly-Si) thin-film transistors (TFT’s) is of growing importance. In this work, the microstructural analysis of the laser irradiated area has been studied with atomic force microscopy (AFM) and phase stepping microscopy (PSM), the latter being an automated mode of interference microscopy that allows the rapid and non-destructive measurement of nanometric surface morphology. The evolution of the crystallisation process in amorphous silicon (a-Si) thin films irradiated using large and long duration (200 ns) excimer laser (308 nm) pulses as a function of different key parameters such as the laser fluence, the beam homogeneity and the number of laser shots has been studied. We show that PSM, although having a lower lateral resolution than AFM, is capable of detecting the important super lateral growth (SLG) region. From the comparison of the results obtained by interference microscopy and AFM, the PSM technique has been shown to be an interesting alternative way that could be used for the quantitative calibration of the laser annealing process in an industrial environment.

Blue-Violet Laser Diodes Suitable for Blu-ray Disk

The authors have developed 405 nm high-power laser diodes suitable for use in Blu-ray Disk systems, the next generation of large-capacity optical recording systems. Epitaxial lateral overgrowth was refined considering the spatial distribution of dislocation density in the lateral growth region to achieve satisfactory lifetimes. Improvements in the threshold/operating current, slope efficiency and characteristic temperature are discussed, in particular with respect to the effect of the location of an AlGaN electron-blocking layer.

Thickness-fringe Contrast Analysis of Defects in GaN

ABSTRACTThe analysis of thickness-fringe contrast in weak-beam transmission electron microscope (TEM) images has been shown to be a reliable method for the complete determination of the character, as well as the magnitude, of a dislocation Burgers vector. By selecting multiple diffraction conditions and, for each condition, determining the number of terminating thickness fringes at the exit of a dislocation from a wedge-shaped sample, the Burgers vector can be unambiguously determined. Defect analysis of GaN pyramids grown on (111)Si by the lateral epitactic overgrowth (LEO) technique reveals a core region which contains a relatively high density of dislocations and a lateral-growth region where the defect density is decreased. The thickness-fringe contrast technique was used in the lateral growth regions of the pyramids to analyze the dislocation Burgers vectors.

AlGaInN high-power lasers grown on an ELO-GaN layer

Epitaxially laterally overgrown (ELO)-GaN substrates with dislocation-free regions can be prepared with a relatively small thickness using atmospheric pressure metal-organic chemical vapor deposition (MOCVD). In order to determine the effect of ELO-GaN layer on the reliability of blue–violet laser diodes (BV-LDs), we fabricated BV-LDs on the lateral-growth region of the ELO-GaN layer. The thickness of the ELO-GaN layer was maintained at 5 μm to inhibit wafer bending, so the total thickness of the BV-LDs was approximately 7 μm. The lifetime of the BV-LDs with a constant output power of 20 mW under CW operation at 25°C was more than 500 h. This lifetime is several times that of our conventional BV-LDs on sapphire substrates. The ELO-GaN layer was very effective in raising the lifetime of BV-LDs.

An XPS study of the nucleation and growth behavior of an epitaxial Pb(Zr,Ti)O 3/MgO(100) thin film prepared by MOCVD

The chemical states and the composition of the surface of the epitaxially-grown lead zirconium titanate (PZT) thin films, prepared by MOCVD on an as-cleaved MgO(100) substrate, were studied by X-ray photoelectron spectroscopy (XPS). At our deposition rate (4.3 nm/min), lateral growth occurred at 20-s depositions, and three-dimensional growth occurred after 30-s depositions. Between the 10 and 40-s depositions, the XPS spectra of Pb (4f) had shoulders at 141 and 136 eV, which strongly suggested that metal Pb co-exists with PZT in the lateral growth region. The binding energy of C (1s) was almost constant, irrespective of the deposition time (deposition mode). However, the binding energies of Pb (4f), Zr (3d), Ti (2p), and O (1s) showed a tendency that binding energy in the lateral growth mode was slightly higher than in the three-dimensional growth mode. The surface atomic ratio Zr/(Zr+Ti) was constant between 10 and 1800 s; on the other hand, the surface atomic ratio Pb/(Pb+Zr+Ti) was almost stoichiometric at the initial stage of deposition, increased with deposition time, and turned out to be constant above 100 s, with a value of Pb/(Pb+Zr+Ti)=0.6.

The structure and crystal growth of nickel electrodeposits from a sulphamate bath on polished polycrystalline copper, in relation to thickness, rate of deposition, temperature and stirring

Grazing-incidence electron diffraction shows the structure and growth of face-centred cubic (fcc) Ni electrodeposits from a sulphamate bath on polished polycrystalline Cu, at 50 and 20°C, both with and without stirring, at current density (cd) i up to 600 mA cm−2 at 50°C, and thickness H up to 60 000 Å or more.Seven isostructural regions of i and H are distinguished, with boundaries approximately of the form H(i-i0)=constant. The effects of bath temperature and of stirring are shown in detail. Ni(OH)2 is co-deposited at cd where the current efficiency falls appreciably below 100%.In the main lateral-growth region the Ni crystals soon develop cube faces (thus layerwise growth) and hence preferred {100} orientation develops (in part also {111} at low i and H). At high cd, {110} and/or {210} outward-growth orientation is developed. The dependence of the spread of orientation about the mean, on i, H, stirring, bath temperature and type of orientation, is shown. It is compatible with these crystal growth and orientation processes and with the cations being incident practically normal to the surface elements of the `rough' deposit.