ALBERT

Notes: The diffusion of δ-function-shaped B- and Sb-dopant spikes in thin Si films grown by solid-phase-epitaxy [(SPE), growth of amorphous film by molecular-beam epitaxy (MBE) at room temperature and subsequent regrowth in situ] during annealing in vacuum is compared to diffusion in films grown by low-temperature (LT) MBE. Diffusion temperatures from 750 to 900 °C, and two-dimensional concentrations of 0.7–1.6×1014 cm−2 have been investigated. The diffusive behavior of dopants in SPE films is found to be qualitatively different from that in films grown by LTMBE. This is related to the vacancylike defects that are intrinsic to growth by SPE but not to growth by LTMBE. Dopant profiles widen significantly during SPE regrowth, making the achievement of δ-function dopant spikes impossible. After a vacuum anneal the diffusion coefficients for both n- and p-type dopants are lower in SPE films than the corresponding values in films grown by LTMBE by up to one order of magnitude. The diffused depth profile of the dopant in LTMBE films shows the characteristic deviation from a pure Gaussian that is expected due to the concentration dependence of diffusion, i.e., a flat top and steep shoulders. In contrast, dopant depth profiles of SPE-grown material show after diffusion a central spike and relatively flat shoulders. The width of the central spike is, after an initial transient that it was not possible to resolve, independent of diffusion time and temperature. This indicates that the SPE material is defective, with the defects acting as traps during diffusion.

Notes: The effects of low-dose ion implants with Si+, Ne+, and F+ on the transient enhanced diffusion of B in silicon after annealing at 900 °C for 30 min have been investigated. Processing conditions such as implant dose (3.5×1013 cm−2) and energy (30–60 keV) were chosen to simulate the lightly doped drain implant in a 0.35 μm complementary metal-oxide-semiconductor technology. An epitaxially grown B-doping superlattice is used to extract directly depth profiles of average Si self-interstitial concentration after processing. For Si+ the transient enhanced diffusion of B increases with the energy of the implanted ion. Ne+ implanted with the same energy as Si+ causes more transient enhanced diffusion, while Ne+ implanted with the same range as Si+ causes slightly less. Implantation of F+ enhances the B diffusivity considerably less than Si or Ne implantation. These effects were modeled using simulations of defect diffusion in the presence of traps. A trap concentration of (2.4±0.5)×1016 cm−3 gave good agreement in all situations except F+ implantation, where (6.6±0.6)×1016 cm−3 traps were necessary. It is proposed that this is caused by additional traps for Si interstitials that are related to F+. © 1995 American Institute of Physics.

Notes: Si self-interstitial diffusivities can be extracted from the diffusive behavior of certain metals (e.g., Au) in an inert annealing ambient or from the diffusion of dopant markers (typically B) under oxidizing conditions. Each type of experiment yields fairly consistent results; however, interstitial diffusivities obtained in these two ways differ greatly. The marker layer experiments rely on the assumption that the presence of the dopant does not disturb the diffusion of the interstitials, and the validity of this assumption is explored. A model of interstitial diffusivity in the presence of B is developed, two extreme cases of the B-atom–interstitial interaction strength are considered, and the predictions of the model are compared with experiments of oxidation-enhanced diffusion in B doping-superlattices. From this comparison it is concluded that trapping of interstitials by B atoms in the markers cannot be responsible for the different values of the Si interstitial diffusivity reported in the literature. Further, it is shown that the presence of the dopant does not perturb the behavior of the Si self-interstitials in the doping-superlattices, i.e., the markers are "unobtrusive'' probes of interstitial behavior. © 1995 American Institute of Physics.

Notes: Using x-ray diffraction techniques, we measure the root-mean-square width of the buried crystalline/amorphous Si(001)/SiO2 interface, as a function of oxide thickness. We find that the interface width decreases with increasing oxide thickness; the oxide growth process kinetically smoothens the buried interface. We also find a difference between the rate of smoothing for wet and dry oxides. © 1995 American Institute of Physics.

Notes: Correlations between observed defect structures and the orientation of planes involved in grain boundary formation in single phase, nearly ideal density Ba2YCu3O7−x are presented. Three types of grain boundary structures are observed: (1) coherent boundaries with only a low-energy network of dislocations at the interface, which are associated with boundaries not involving a basal plane face, (2) semicoherent boundaries surrounded by a 50–1500 A(ring) wide band of dislocation loops on the c-axis side of the basal-plane-faced boundary, and (3) incoherent boundaries where severe local strain has produced substantial plastic deformation and generation of small voids, again associated with basal-plane-faced boundaries. These results are interpreted using a model for local stress based on the known highly anisotropic thermal contraction of the material during cooling from sintering temperatures.

Notes: High Tc superconducting Y-Ba-Cu-O films have been produced by rf magnetron sputtering using single unreacted composite targets of Y2O3, BaF2, and CuO powders. Transport measurements of the films showed a sharp resistive Tc (R=0) at 89 K and a metallic behavior of resistivity versus temperature. The films show preferred orientations when deposited on single-crystal SrTiO3 substrates (100) or (110) and followed by a post O2 annealing at 825 °C.

Notes: Room-temperature Hall mobilities of (100) HgTe films grown by molecular beam epitaxy can reach values of 27 000–31 000 cm2 V−1 s−1, while the mobilities of (111) films are only 14 000–16 000 cm2 V−1 s−1. We show that the defects which lead to the lower mobilities of (111) films are present in the first 1000 A(ring) of growth. Transmission electron microscope studies reveal a cellular structure of high-angle grain boundaries with some twinning about the (111) growth axis. These defects, and hence the reduced mobilities of the films, appear to result from island nucleation of the films.

Notes: We present the materials growth and properties of both epitaxial and amorphous films of Gd2O3 (κ=14) and Y2O3 (κ=18) as the alternative gate dielectrics for Si. The rare earth oxide films were prepared by ultrahigh vacuum vapor deposition from an oxide source. The use of vicinal Si (100) substrates is key to the growth of (110) oriented, single domain films in the Mn2O3 structure. Compared to SiO2 gate oxide, the crystalline Gd2O3 and Y2O3 oxide films show a reduction of electrical leakage at 1 V by four orders of magnitude over an equivalent oxide thickness range of 10–20 Å. The leakage of amorphous Y2O3 films is about six orders of magnitude better than SiO2 due to a smooth morphology and abrupt interface with Si. The absence of SiO2 segregation at the dielectric/Si interface is established from infrared absorption spectroscopy and scanning transmission electron microscopy. The amorphous Gd2O3 and Y2O3 films withstand the high temperature anneals to 850 °C and remain electrically and chemically intact. © 2001 American Institute of Physics.

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.