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One strategy for decreasing the density of threading dislocations penetrating the surface of a heteroepitaxial semiconductor film is that in which the greater mechanical stiffness of a dislocation blocking layer acts to reduce the Peach–Koehler image forces acting on the leading segment of the half loop generated by dislocation multiplication sources at the heteroepitaxial interface situated below the blocking layer. Reducing the Peach–Koehler force, drawing the half loop to the film surface, helps prevent the two threading arms of the half loop from becoming threading dislocations once the half loop penetrates the film surface. The calculation of the Peach–Koehler force employs an analytical continuation formalism using anisotropic elasticity theory for treating dislocation image forces generated by three heteroepitaxial interfaces corresponding to the top and bottom interfaces of the blocking layer and the film surface. The system used in this calculation is that of a Ge film grown on a (001) Si substrate, using a SiGe blocking layer just below the critical thickness for dislocation generation. It is found that the dislocation blocking is favored by thinner blocking layers of greater mechanical stiffness, rather than thicker blocking layers of moderate mechanical stiffness. Specifically, for the blocking layers of composition Si0.2Ge0.8, Si0.3Ge0.7, and Si0.4Ge0.6, of thickness 50, 18, and 10 nm, respectively, it is the thinnest (and mechanically stiffest) layer (Si0.4Ge0.6, 10 nm) that brings about the greatest reduction in the Peach–Koehler force, drawing the leading segment of the half loop to the surface of the film. [ABSTRACT FROM AUTHOR]

Amorphous films of Nb2O5 composition were deposited by thermal atomic layer deposition on (001) Si substrates and subsequently crystallized by annealing in forming gas at temperatures ranging from 550 °C to 1000 °C. After subjecting these films to an 850 °C anneal, cross-sectional transmission electron microscopy revealed the presence of B-Nb2O5 and T-Nb2O5 phases in the matrix, as well as reduced R-NbO2 in floret-shaped regions. Annealing at 1000 °C completed the reduction process, resulting in the insulator-to-metal transition (IMT) capable T-NbO2 phase throughout the film. ALD films of composition Nb2O5 were also deposited on electron-transparent SiN membranes and then subjected to 550 °C and 1000 °C anneals. Here, the 550 °C anneal induced the B-Nb2O5 and T-Nb2O5 phases without inducing the R-NbO2 phase. The 1000 °C anneal of the films deposited on SiN membranes retained B-Nb2O5 while inducing the R-NbO2 phase, but without bringing the process to completion and inducing the T-NbO2 phase. The effectiveness of the 1000 °C reducing annealing treatment to induce the T-NbO2 phase for Nb2O5 films deposited on (001) Si substrates, while stopping short of this transition for films deposited on SiN membranes, suggests the importance of the SiO2 layer on the Si substrate in contributing to the reduction reaction that results in the technologically important insulator-to-metal transition (IMT)-capable T-NbO2 phase. [ABSTRACT FROM AUTHOR]

Defect sensitive etching (DSE) was developed to estimate the density of non-basal plane dislocations in hexagonal boron nitride (hBN) single crystals. The crystals employed in this study were precipitated by slowly cooling (2-4 °C/h) a nickel-chromium flux saturated with hBN from 1500 °C under 1 bar of flowing nitrogen. On the (0001) planes, hexagonal-shaped etch pits were formed by etching the crystals in a eutectic mixture of NaOH and KOH between 450 °C and 525 °C for 1-2 min. There were three types of pits: pointed bottom, flat bottom, and mixed shape pits. Cross-sectional transmission electron microscopy revealed that the pointed bottom etch pits examined were associated with threading dislocations. All of these dislocations had an a-type burgers vector (i.e., they were edge dislocations, since the line direction is perpendicular to the [2110]-type direction). The pit widths were much wider than the pit depths as measured by atomic force microscopy, indicating the lateral etch rate was much faster than the vertical etch rate. From an Arrhenius plot of the log of the etch rate versus the inverse temperature, the activation energy was approximately 60 kJ/mol. This work demonstrates that DSE is an effective method for locating threading dislocations in hBN and estimating their densities. [ABSTRACT FROM AUTHOR]

Although the crystalline a and c phases are the most stable forms of alumina, small-diameter (<6 nm) nanoparticles are known to be completely amorphous, due to the surface energy being correspondingly lower for the less stable non-crystalline phase. Al2O3 films with a thickness of 5 nm grown by low temperature (200 °C) atomic layer deposition (ALD) on small-diameter (<20 nm) Ga2O3 nanowires (NWs), however, are identified by transmission electron microscopy as belonging to the a, c, and possibly h crystalline phases of Al2O3, while films deposited on larger diameter (>20 nm) NWs are found to be amorphous. Indeed, until recently, all Al2O3, films deposited by low-temperature ALD using trimethylaluminum and water have been reported to be amorphous, regardless of film thickness or substrate. The formation of a crystalline ALD film can be understood in terms of the energetics of misfit dislocations that maintain the registry between the ALD film and the NW substrate, as well as the influence of strain and surface energy. The decreasing energy of co-axial misfit dislocations with NW diameter results in a corresponding decrease in the contribution of the Al2O3/Ga2O3 interface to the free energy, while the interfacial energy for an amorphous film is independent of the NW diameter. Therefore, for NW cores of sufficiently small diameter, the free energy contribution of the Al2O3/Ga2O3 interface is smaller for crystalline films than for amorphous films, thereby favoring the formation of crystalline films for small-diameter NWs. For ALD Al2O3 films of 10 nm thickness deposited on small-diameter Ga2O3 NWs, however, only the first 5 nm of the ALD film is found to be crystalline, possibly due to well-established kinetic limitations to low temperature epitaxial growth. [ABSTRACT FROM AUTHOR]

Using methods developed for modeling diffraction contrast of extended defects in thin foils, electron intensity profiles are simulated and found to qualitatively match channeling contrast of threading screw dislocations (TSDs) experimentally recorded by electron channeling contrast imaging (ECCI) using scanning electron microscopy. Plan-view images of TSDs axially penetrating (0001) 4H-SiC surfaces were computed using the Sturkey scattering matrix approach incorporating surface relaxation effects. Simulated diffraction contrast of the TSD allows identification of these threading defects as well as facilitates the determination of the dislocation Burgers vector. The directionality of TSD contrast features, simulated for various Bragg reflections and deviation parameters, is consistent with both ECCI and diffraction contrast imaging by transmission electron microscopy. Topographically enhanced imaging of atomic step spirals, generated by the TSDs, provides a direct determination of the TSD Burgers vector, which is shown to agree with the simulated ECCI contrast. The convergence of the incident electron beam is also shown to influence channeling contrast. [ABSTRACT FROM AUTHOR]

The impetus for dislocation motion in thin films is generally understood in terms of Peach-Koehler forces. For the case of III-nitride films grown on step-free 4H-SiC mesas, however, it is the gradient of the strain energy from the mesa edge that is capable of driving misfit dislocations. Using the strain profile as a function of the distance from the mesa edge and the line tension of the c-plane threading arms, we have calculated the excess stress driving the half loop from the mesa edge into the mesa interior. We have also compared the half-loop excess stress with the excess stress driving the tilt of threading edge dislocations, which has been proposed as one of the principal strain relief mechanisms in III-nitride films. The excess stress driving c-plane half loops ranges from a few 1000 MPa at the mesa edge to few 100 MPa towards the mesa interior, while the excess stress driving the tilt of threading edge dislocations is in excess of 20 000 MPa. The greater excess stress driving dislocation tilt, however, does not dominate strain relief for III-nitride films on step-free SiC mesas due to the difficulty in nucleating threading dislocations in the absence of interfacial steps. [ABSTRACT FROM AUTHOR]

Presents a study that described the nucleation and growth of germanium on (1102) sapphire deposited by molecular beam epitaxy. Optimal conditions under which the germanium was grown; Experimental procedures for the film growth; Formation of germanium islands on (1102) sapphire.

Deals with a study which derived an expression for the dislocation line tension in thin film structures for double-kink extension of a threading dislocation. Calculations of the dislocation dipole; Impact of the double-kink mechanism on strain quantum well or modulated structures.

Presents a study which investigated the strain relief of compressive biaxial strains in thin films through microtwins. Experimental details; Results and discussion; Conclusions.

Evaluates the microtwin density as a function of distance from the interface in silicon grown on sapphire. Details on the experiment; Information on the microtwin morphology; Conclusions.

Presents a study which examined the structural faults and domain boundaries in congruent lithium niobate using a transmission electron microscope. Discussion on the development of optical-wave-guide devices; Experimental details; Analysis of the extended defects of titanium-diffused congruent lithium niobate.

Focuses on the measurement of lattice parameters to several parts for thin-film samples consisted of a planar quartenary layer grown on an indium phosphide substrate. Use of x-ray diffraction techniques; Position of higher-order Laue zone (HOLZ) lines as a function of the lattice parameter; Extraction of a set of lattice parameters from the HOLZ lines of a convergent-beam electron diffraction pattern.

Focuses on a study that investigated the defect mechanisms in degradation of wavelength channeled-substrate buried heterostructure lasers. Methodology; Results and discussion; Conclusion.

We report the growth of crystalline Al2O3 thin films deposited by thermal Atomic Layer Deposition (ALD) at 200 °C, which up to now has always resulted in the amorphous phase. The 5 nm thick films were deposited on Ga2O3, ZnO, and Si nanowire substrates 100 nm or less in diameter. The crystalline nature of the Al2O3 thin film coating was confirmed using Transmission Electron Microscopy (TEM), including high-resolution TEM lattice imaging, selected area diffraction, and energy filtered TEM. Al2O3 coatings on nanowires with diameters of 10 nm or less formed a fully crystalline phase, while those with diameters in the 20-25 nm range resulted in a partially crystalline coating, and those with diameters in excess of 50 nm were fully amorphous. We suggest that the amorphous Al2O3 phase becomes metastable with respect to a crystalline alumina polymorph, due to the nanometer size scale of the film/substrate combination. Since ALD Al2O3 films are widely used as protective barriers, dielectric layers, as well as potential coatings in energy materials, these findings may have important implications. [ABSTRACT FROM AUTHOR]

Forescattered electron detection (FED) was utilized to image surface depressions resulting from threading screw and edge dislocations in 4H-SiC epitaxial layers. These surface depressions, or growth pits, exhibited two morphology types. Screw and edge dislocations could be imaged by photoluminescence and differentiated by their interactions with propagating partial dislocations (PDs). Correlations between FED and photoluminescence showed that sharp-apex pits 1 µm in size and strip-shaped pits 500 nm in size could be linked to individual screw and edge dislocations, respectively. Forescattered electron detection demonstrated sufficient sensitivity to image surface features previously resolvable only by atomic force microscopy. This new technique is nondestructive, noncontact, and capable of rapid, spatial mapping of growth pits resulting from threading screw and edge dislocations in SiC epitaxial layers. [ABSTRACT FROM AUTHOR]

High-reflectance group III-nitride distributed Bragg reflectors (DBRs) were deposited by metal-organic chemical-vapor deposition on Si(111) substrates. A reflectance greater than 96% was demonstrated for an AlN/GaN DBR with a stop band centered in the blue-green range of the visible spectrum. Crack-free GaN cap layers were grown on the DBR structures to demonstrate the opportunity to build III-nitride optoelectronic devices in this material. The DBR structure was under significant strain due to growth on a mismatched substrate, although the GaN cap layer was shown to be strain-free. [ABSTRACT FROM AUTHOR]

Threading dislocations in metal-organic chemical-vapor grown GaN films were imaged nondestructively by the electron channeling contrast imaging (ECCI) technique. Comparisons between ECCI and cross-sectional transmission electron microscopy indicated that pure edge dislocations can be imaged in GaN by ECCI. Total threading dislocation densities were measured by ECCI for various GaN films on engineered 4H-SiC surfaces and ranged from 107 to 109 cm-2. A comparison between the ultraviolet electroluminescent output measured at 380 nm and the total dislocation density as measured by ECCI revealed an inverse logarithmic dependence. [ABSTRACT FROM AUTHOR]

Threading dislocations in thin (<200 nm) AlN nucleation layers (NLs) grown by metal-organic chemical vapor deposition on top of 4H-SiC on-axis mesas with atomic-scale steps were analyzed by transmission electron microscopy. The AlN NL controlled threading dislocations in an overlying ∼2 μm GaN layer through two identified mechanisms: threading half-loop formation and dislocation bending at V-shaped pits. Threading dislocations in the AlN film could be traced directly to bilayer 4H-SiC steps at the substrate/film interface. These observations reveal several approaches to extended defect reduction in GaN films grown on 4H-SiC. [ABSTRACT FROM AUTHOR]

Direct imaging of atomic step morphologies and individual threading dislocations in on-axis epitaxial 4H-SiC surfaces is presented. Topographically sensitive electron images of the crystalline surfaces were obtained through forescattered electron detection inside a conventional scanning electron microscope. This technique, termed electron channeling contrast imaging (ECCI), has been utilized to reveal the configuration of highly stepped, homoepitaxial 4H-SiC films grown on 4H-SiC mesa structures. Individual threading dislocations have been consistently imaged at the core of spiral atomic step morphologies located on the 4H-SiC surfaces. The ability of ECCI to image atomic steps was verified by atomic force microscopy. [ABSTRACT FROM AUTHOR]

An approach to reduce vertical threading dislocations in the active regions of III-nitride devices is described. The approach involves confined homo- or heteroepitaxy of GaN materials using sputtered oxide masks to delineate growth regions and conventional metal-organic chemical vapor deposition. The resulting confined epitaxial material is terminated with equilibrium crystal facets, which form hexagonal mesas, and contains a reduced dislocation density and reduced strain compared to the underlying template layer for homoepitaxial growth. Characterization of pn junction diodes grown with this approach reveals significantly reduced leakage currents in as-grown, unpassivated structures (as low as 1×10-7 A cm-2). [ABSTRACT FROM AUTHOR]

The authors report on the growth of InAs nanowires using nanometer-sized Si clusters in a closed system without any metal catalyst. The growth was performed at 580 °C for 30 min using 1.3 nm thickness of SiOx. It is suggested that the nanowire growth occurred due to highly reactive nanometer-sized Si clusters, which are formed by phase separation of SiOx. The authors have also examined the vapor-liquid-solid (VLS) mechanism under various oxidizing conditions, including different oxygen pressures (200 and 800 mTorr) and oxidized Au–In tip. The results indicate the inhibiting effect of oxygen on the VLS mechanism. [ABSTRACT FROM AUTHOR]