Bibliothek

Notizen: Double crystal x-ray analysis has been carried out on GaAs wafers implanted with 1.15 MeV sulfur ions at a dose of 5×1014/cm2, followed by rapid thermal anneal for 10 s at temperatures between 300 and 1100 °C. A systematic reduction of strain with increased annealing temperature has been observed, as measured from the separation between the peak of the unimplanted substrate and the major peak of the strained region. Calculations of strain distribution based on existing numerical models are correlated with implantation parameters using Pearson's type-VI distribution functions. Strain reduction after a silicon nitride encapsulation process is found to be equivalent to that after a 300 °C, 10 s rapid thermal anneal (RTA). It is also found that strain relaxation by RTA is strongly dependent on both sample size and the annealing geometry.

Notizen: We have investigated magneto-transport and cyclotron resonance (CR) of two-dimensional electron gas in silicon δ-doped p-InSb under a magnetic field of up to 12 T at 4.2 K. Because there are multiple subbands occupied, Shubnikov–de Haas oscillations show a beating behavior. The CR spectra also display several peaks originating from different subbands. Effective masses of electrons associated with the lowest three subbands can therefore be directly determined, and they are in excellent agreement with a self-consistent calculation, which takes into account the electrostatic Poisson equation, the Schrödinger equation, and realistic sample parameters. Furthermore, we observed an absorption peak, whose resonance position has anomalous angle dependence. It is attributed to impurity CR where donors are in the vicinity of the δ-doped sheet.

Notizen: A 300 A(ring) buffer layer of InSb grown by atomic layer epitaxy at a substrate temperature of 300 °C at the GaAs/InSb interface has been employed to grow epitaxial films of InSb having bulk-like properties. The reduction of the defects in the top InSb film has been observed with cross-sectional transmission electron microscopy and channeling Rutherford backscattering spectroscopy. The optimum substrate temperature for the primary InSb layer growth was 420 °C with an atomic flux ratio of Sb to In of 1.4 and a growth rate of 1 μm/h. The best 5-μm-thick InSb layers had x-ray rocking curve widths of 100 s, 77 K n-type carrier concentrations in the low 1015/cm3 range, and 77 K carrier mobilities greater than 105 cm2/V s. Mesa isolated photodiodes had carrier lifetimes of 20 ns, in comparison to 200 ns observed in bulk InSb having a similar carrier concentration. An unexplained, weak free-electron spin resonance transition has been observed in these films.

Notizen: Cordierite H2O and CO2 volatile saturation surfaces derived from recent experimental studies are presented for P–T conditions relevant to high-grade metamorphism and used to evaluate fluid conditions attending partial melting and granulite formation. The volatile saturation surfaces and saturation isopleths for both H2O and CO2 in cordierite are strongly pressure dependent. In contrast, the uptake of H2O by cordierite in equilibrium with melts formed through biotite dehydration melting, controlled by the distribution of H2O between granitic melt and cordierite, Dw[Dw = wt% H2O (melt)/wt% H2O(Crd)], is mainly temperature dependent. Dw = 2.5–6.0 for the H2O contents (0.4–1.6 wt percentage) typical of cordierite formed through biotite dehydration melting at 3–7 kbar and 725–900 °C. This range in Dw causes a 15–30% relative decrease in the total wt% of melt produced from pelites. Cordierite in S-type granites are H2O-rich (1.3–1.9 wt%) and close to or saturated in total volatiles, signifying equilibration with crystallizing melts that achieved saturation in H2O. In contrast, the lower H2O contents (0.6–1.2 wt percentage) preserved in cordierite from many granulite and contact migmatite terranes are consistent with fluid-absent conditions during anatexis. In several cases, including the Cooma migmatites and Broken Hill granulites, the cordierite volatile compositions yield aH2O values (0.15–0.4) and melt H2O contents (2.2–4.4 wt%) compatible with model dehydration melting reactions. In contrast, H2O leakage is indicated for cordierite from Prydz Bay, Antarctica that preserve H2O contents (0.5–0.3 wt%) which are significantly less than those required (1.0–0.8 wt%) for equilibrium with melt at conditions of 6 kbar and 860 °C. The CO2 contents of cordierite in migmatites range from negligible (〈 0.1 wt%) to high (0.5–1.0 wt%), and bear no simple relationship to preserved cordierite H2O contents and aH2O. In most cases the cordierite volatile contents yield total calculated fluid activities (aH2O + aCO2) that are significantly less than those required for fluid saturation at the P–T conditions of their formation. Whether this reflects fluid absence, dilution of H2O and CO2 by other components, or leakage of H2O from cordierite is an issue that must be evaluated on a case-by-case basis.

Notizen: Purpose This study evaluated the bond strength and bond durability of new adhesive systems to pure titanium.Materials and Methods Plexiglass tubes filled with composite were bonded to titanium discs. Groups of 24 samples were bonded using six different bonding systems. Subgroups of eight bonded samples were stored in an isotonic artificial saliva solution (37°C) for 1, 30, or 150 days. In addition, the 30- and 150-day samples were thermal cycled for 7,500 or 37,500 cycles between 5°C and 55°C, respectively. After these storage conditions, all samples were debonded in tension.Results The bond strength of a conventional bisphenol-A glycidyl methacrylate composite to sandblasted titanium was significantly lower than using chemomechanical bonding systems and decreased slightly during the storage time of 150 days. The additional use of a silane on sandblasted titanium resulted in an insignificant increase in bond strength and decreased over storage time to the same level as on sandblasted-only titanium. Statistically significant higher bond strengths were achieved either with the combination of silica coating and use of a conventional bisphenol-A glycidyl methacrylate composite or with the combination of sandblasting and the use of composites modified with a phosphate monomer. In the latter systems, the bond strengths were only limited by the cohesive strength of the composite resins. A new phosphate monomer containing composite showed a tendency to lose cohesive strength over time (statistically not significant).Conclusions Using chemomechanical bonding systems, ie, silica-coating systems or modified composites with adhesive monomers, resulted in 2 to 2.5 times increased bond strength to titanium compared with the bond strength of a conventional bisphenol-A glycidyl methacrylate composite. With chemomechanical bonding systems, the resin bond to titanium was durable over 150 days, even after being stored in water and thermal cycled.

Notizen: The segregation of B from Si1−xGex quantum wells grown using molecular beam epitaxy on Si(100) and Si(110) was investigated using secondary ion mass spectrometry. When a 3 nm B doping slab (n=1019/cm3) was placed in the center of a 6 nm Si1−xGex quantum well, the B profiles had two distinct exponential decay lengths, ΔSiGe, the Ge-controlled B decay length and ΔSi, the B decay length normally measured in Si. ΔSiGe was the same for Si(100) and Si(110) and independent of Ge concentration in the well for 0.1≤x≤0.5. As the Ge concentration was increased in the well, the location of the transition point, from ΔSiGe to ΔSi, which was always found far outside of the SiGe quantum well, increased in distance from the center of the well.

Notizen: Exposure to dry etching can deleteriously affect strained SiGe films by initiation of misfit strain discontinuity in the film as well as at the interface. In this paper annealing behavior of defects generated as a consequence of dry etching of Si/SiGe/Si heterostructure metal–oxide–semiconductor capacitors have been reported. Some samples were wet etched for comparison. Samples were annealed at four different temperatures after being etched, namely, 650, 700, 750, and 800 °C. Results of the investigations using deep-level transient spectroscopy reveal defect levels at 0.62, 0.57, 0.56, and 0.44 eV for the dry-etched samples and at 0.31, 0.43, 0.56, and 0.44 eV for the wet-etched samples annealed at the aforetold temperatures. The results could be explained on the basis of appearance of point defects condensing into dislocation loops which eventually shrink and disappear as the annealing temperature is increased. The estimated size of the dislocation loops agrees quite well with the experimentally measured values obtained for identically processed samples. © 1996 American Institute of Physics.