ALBERT

Notes: The microstructure of oxidized amorphous Tb-Fe alloy thin films prepared by magnetron cosputtering has been studied as a function of alloy composition and the substrate temperature at which the films were grown. Transmission electron microscopy and Auger electron spectroscopy with ion-sputter depth profiling were used to characterize the films. The composition of the alloy has no dramatic effect on the oxidation rate; it does, however, effect the microstructure of the α-Fe2O3 layer that forms on the alloy. Oxidized alloys originally containing more than 27 at. % Tb show an extremely fine-grained structure, with grain sizes on the order of 30 A(ring). Alloys containing less Tb developed large (1–2 μm) [001]-oriented single-crystal α-Fe2O3 grains amongst the fine-grained α-Fe2O3. For alloys with less then 18 at. % Tb, only the large grains remain. Samples grown at deposition temperatures ranging from 85 K to 400 °C show a similar structure after oxidation.

Notes: The correlation of deposition parameters, microstructure, and stability of rf-diode sputtered magneto-optical thin films has been studied by using transmission electron microscopy and a magneto-optical hysteresis loop tracer. Among the sputtering parameters, we found that both argon bleeding pressure and substrate bias have strong influences on microstructure and consequently the oxidation resistance of the films. Sputtering using moderate argon pressure and substrate bias produces dense and smooth films. The bare films are strongly resistant to oxidation. In contrast, low or high argon pressure and substrate table bias result in films of high porosity, columnar "islandlike'' structure, or "spongelike'' morphology. They degrade rapidly in air.

Notes: Damage introduction by implantation of Be and Si into InSb, and its removal by rapid thermal annealing in the range 300–400 °C for 20 s was investigated by Rutherford backscattering and transmission electron microscopy. There is good recovery of the lattice upon annealing at 450 °C provided the InSb was not amorphized during the implantation step. At the same time, there is limited redistribution of Be for these annealing conditions, but for Si there is marked diffusion even during a nominal room-temperature implant. Lowering the sample temperature to 77 K during the implant stops this redistribution, with a near-Gaussian ion distribution resulting. The activation of Be is of the order of 50% over the dose range 1013–1015 cm−2. In most cases there is a marked similarity in implant properties of InSb to those of GaSb.

Notes: Transmission electron microscopy is used to characterize the defects in high Tc superconductor, Ba2YCu3O6.9 produced by two different ceramic processing procedures. In both samples the microstructure is dominated by lamellar domains. These have been identified as reflection twins by observations both of rotations of the diffraction patterns and of δ-fringe contrast. The reflection plane is (110). The characteristic width associated with the twins correlates with annealing time. Occasionally within the twinned domain, substructure on a 50-A(ring) scale is visible, which is attributed to further subdivision into twinned and matrix domains. The twin structure does not interrupt the continuity of the Cu-O planes between Y and Ba layers, but does terminate Cu-O chains in the inter-Ba Cu-O planes. Convergent beam electron diffraction results are consistent with a Pmmm space group. Microcracks and disloction loops are also observed in the (001) basal plane, indicating that the (001) plane is both the slip and cleavage plane in this material.

Notes: Amorphous GdCo films with perpendicular anisotropy have been prepared by dc diode getter sputtering under argon or neon pressure. To study the aging behavior, the films with no protecting layer were used and exposed to air at room temperature. We have observed that the perpendicular anisotropy in these uncoated GdCo films significantly increases with time. Furthermore, the negative (in-plane) anisotropy which existed at the initial stage during aging actually decreases with time and finally disappears.

Notes: Thin films of amorphous/polycrystalline Ti layers alternating with amorphous Si have been grown on room-temperature {001} Si substrates by electron beam evaporation. Cross-section transmission electron microscopy of these films indicates that the deposition results in the formation of ultrathin superlattice layers with no cumulative roughening and with atomically abrupt interfaces. The crystallinity of the layers containing Ti is found to depend on the layer thickness. For thicknesses ≤20 A(ring) they appear amorphous, whereas layers thicker than ∼40 A(ring) consist of polycrystalline hexagonal Ti grains exhibiting a (0001) preferred orientation parallel to the interfaces.

Notes: GexSi1−x thin films were grown by molecular beam epitaxy on Si substrates which were purposely miscut ∼3° off the (111) face, toward the [011] pole. Rutherford backscattering channeling angular scans show that the miscut causes the Ge-rich alloy films to grow with an apparent crystallographic tilt relative to the substrate. Transmission electron microscopy micrographs reveal that these films contain many slip-induced stacking faults along a preferential direction. These results are explained in terms of a difference in the magnitude of the resolved shear stress, caused by the lattice mismatch and the 3° miscut.

Notes: Distinct antiphase domain structures in GaAs epitaxial layers grown on a Si/SiO2/Si-substrate structure by metalorganic chemical vapor deposition have been revealed by using a silicon etchant (HF/HNO3). The antiphase is characterized by the [011]-oriented etching textures which rotate 90° between adjacent domains. The corresponding lattice rotation is further confirmed by a convergent beam electron diffraction technique. The size of the antiphase domains is found to increase with increasing film thickness and to grow upon annealing at temperatures above 700 °C. The maximum size of the domain, however, is found to be limited by the film thickness. The majority of the domain boundary lines revealed by chemical etching on the (100) surface do not correspond to any crystalline orientation. Only small segments are found to orient along [011], [010], [021], and, occasionally, [031] and [041] directions. Cross-sectional transmission electron microscopy studies confirmed that the boundaries are generally in curved configurations or zigzag configurations constituted of (011), (010), and (121) planes. All the boundaries are initiated at the interface and propagate through the film in the growth direction. Diffraction contrast experiments show a stacking-faultlike contrast of intrinsic type, indicating an inward relaxation of the lattice planes at the boundary. The rapid chemical reaction of the boundary with the silicon etchant, the intrinsic nature of the lattice distortion at the boundary, and the curved configuration of the boundary indicate that the boundary atoms are replaced by Si atoms. The higher concentration of Si atoms at the antiphase boundary has further been verified by energy dispersive x-ray analysis. In view of the reduction of bond distortion energy, the segregation of Si atoms at the antiphase boundary eliminates the highly distorted GaGa and AsAs bonds and is, therefore, an energetically favorable process. The possible antiphase boundary structure and a mechanism for its migration are discussed. Spatially resolved photoluminescence and cathodoluminescence studies reveal that both the antiphase boundaries and the defective interfacial regions contain nonradiative recombination centers. The luminescence efficiency of the domains increases strongly after annealing.

Notes: Channeled-substrate buried heterostructure (CSBH) lasers which were purged from populations undergoing high reliability qualification have been studied in detail. Gradual and rapid degradation mechanisms leading to accelerated aging failure modes have been analyzed by transmission electron microscopy, convergent beam electron diffraction, electroluminescence, energy dispersive x-ray analysis, and chemical etching. The gradual degradation mode of CSBH lasers is characterized by (1) a gradual increase in room-temperature threshold current; (2) a decrease in external quantum efficiency, typically a drop in peak value of dL/dI greater than 25%; (3) a drop in forward voltage at low current, indicating a change in junction characteristics; (4) a large peak inI(dV/dI) below threshold (at around 3 mA); and (5) an enhancement in the peak in I2(d2V/dI2) at laser threshold. A defect mechanism associated with the gradual degradation begins with a nucleation of extrinsic dislocation loops along the V-groove {111} p-n–type sidewall interfaces between the Cd-diffused p-InP and liquid-phase-epitaxial-grown n-InP buffer inside the groove. These dislocation loops subsequently grow out of the interfaces into the n-InP buffer region in the direction of minority-carrier injection, indicating a nonradiative recombination-assisted defect growth process. For those loops which enter the quaternary active region near the tip of the active crescent, the growth rate along the (001) and (010) planes is greatly enhanced and the loops eventually cut across the active stripe and become dark-line defects, as confirmed by electroluminescence. Nucleation of dislocation loops is not observed along the {111} p-p–type sidewall interfaces above the active stripe. The fact that the dislocation loops are all extrinsic in nature implies that the {111} sidewall interfaces as well as the quaternary active region contain a high density of interstitials. The possible causes for the generation and growth of the dislocation loops and the high density of point defects are discussed. The rapid degradation mode of the CSBH laser is characterized by a sudden drop in light intensity during the aging process. The associated defect mechanism starts with localized melting at the mirror facet or inside the lasing cavity. A metal-rich droplet subsequently forms which propagates along the center of the active stripe in the direction towards the cavity center via a meltback-regrowth process; i.e., material melts in front of the droplet and regrows after it propagates by. The nonideal condition of regrowth results in the formation of a wormlike defect composed of a cylinder of defective materials bounded by an off-stoichiometric interface. The wormlike defect is dark under electroluminescence. Complicated dislocation structures can also be grown from the wormlike defect under a nonradiative recombination-assisted defect growth process. These phenomena are presented and discussed.