Prismatic Stacking Faults Research Articles

Direct Observations Of Atomic Structures Of Defects In Gan By High Resolution Z-Contrast Stem

AbstractGaN/(0001)Sapphire grown by low pressure MOVPE is studied by high resolution Z-contrast imaging using STEM. First direct observation of the threading dislocation with edge character shows the atomic core structure, which appears to have a similar configuration to the {10–10} surface. The surfaces of the nanopipe walls are on {10–10} with the terminating layer between the atoms with one bond per pair. In addition, the high resolution Z-contrast image of the prismatic stacking fault confirms the results by conventional HRTEM.

Local Electronic Structure Of Defects In Gan From Spatially Resolved Electron Energy-Loss Spectroscopy

AbstractThe optical properties and their modification by crystal defects of wurtzite GaN are investigated using spatially resolved electron energy-loss spectroscopy (EELS) in a dedicated ultra-high vacuum field emission gun scanning transmission electron microscope. The calculated density of states of the bulk crystal reproduces well the features of the measured spectra. The profound effect of a prismatic stacking fault on the local electronic structure is shown by the spatial variation of the optical properties derived from low-loss spectra. It is found that a defect state at the fault appears to bind 1.5 electrons per atom.

Structure of the 2H-Ain/6H-SiC Interface

AbstractSteps at the AIN/SiC interface have been investigated by HREM. Some of them do not introduce any defects. Others steps present a dislocation character which can contribute to relieve the strain due to the lattice mismatch. A third kind of steps gives rise to a prismatic planar fault for which a model is given. A reaction between prismatic and basal stacking faults is analyzed.

Molecular beam epitaxy of GaN(0001) utilizing NH3 and/or NH+x ions: Growth kinetics and defect structure

Gas-source molecular beam epitaxy (GS-MBE), utilizing Ga and NH3, and reactive-ion MBE (RIMBE), incorporating both thermal NH3 and low-energy NH+x ions, were used to grow single crystal GaN(0001) layers on Al2O3(0001) at temperatures Ts between 700 and 850 °C with deposition rates of 0.2–0.5 μm h−1. The RIMBE experiments were carried out with incident NH+x/Ga flux ratios JNH+x/JGa=1.9–3.2 and NH+x acceleration energies ENH+x=45–90 eV. Plan-view and cross-sectional transmission electron microscopy analyses showed that the primary defects in the GS-MBE films were threading dislocations having either pure edge or mixed edge/screw characteristics with Burgers vectors b̄=1/3〈21̄1̄0〉, basal-plane stacking faults with displacement vectors R̄=1/6〈022̄3〉, and prismatic stacking faults with R̄=1/2〈1̄101〉. In the case of RIMBE films, no stacking faults or residual ion-induced defects were observed with ENH+x=45 eV and Ts≥800 °C. However, increasing ENH+x to ≥60 eV at Ts=800 °C gave rise to the formation of residual ion-induced point-defect clusters observable by transmission electron microscopy (TEM). Increasing Ts to 850 °C with ENH+x≥60 eV resulted in the ion-induced defects aggregating to form interstitial basal and prismatic dislocation loops, whose number densities depended upon the ion flux, with Burgers vectors 1/2〈0001〉 and 1/3〈21̄1̄0〉, respectively. Unlike previously published results for RIMBE growth with N+2, GaN growth kinetics with NH+x were not found to be a strong function of either ion-to-thermal flux ratios or ion acceleration energies.

Formation of dislocation loops on prismatic faults in zinc oxide in a high voltage electron microscope

Abstract During 500 kV electron microscope observation of vapour-grown zinc oxide, dislocation loops nucleate at every—c side corner of prismatic stacking faults that intersect with basal faults, and grow on the prismatic faults. Diffraction contrast experiments show these loops to be of interstitial type with a Burgers vector of — 1/2c + (1 – 1/√3)a, where a is normal to the fault plane. From the threshold voltage of about 300 kV for the loops to be formed, it is concluded that the loop formation is due to migration of interstitial oxygen atoms that have undergone displacement by electron irradiation and of excess zinc atoms originally present interstitially in the crystal.

Electron Microscopic Contrast Effects at the Interface between Two Different Polytypes. II. Interface 2H–4H

AbstractThe contrast effects associated with the interface between two different polytypes of zinc sulfide, 2H and 4H are discussed. A special type of fringes characterized by a different spacing at the top and bottom end is associated with such interfaces. The fringe patterns associated with overlapping interfaces are discussed as well. The transformation 2H–4H is found to be a shear transformation. The prismatic stacking faults in wurtzite are found to be growth faults; they are eliminated by the passage of transformation partials on the basal plane.