The hydrostatic pressure dependence of the diffusivity of B and Sb in Si and of B in Si 89 Ge 11 has been measured. The diffusivity of Sb in Si is retarded by pressure, characterized by an apparent activation volume of Ṽ Sb = + 0.06± 0.04 times the Si atomic volume ⍀. The diffusivity of B is enhanced by pressure, characterized by an apparent activation volume of Ṽ B of ͑−0.16± 0.05͒ ⍀. The diffusivity of B in strain-relaxed Si 89 Ge 11 is imperceptibly pressure dependent, characterized by an apparent activation volume of ͑+0.03± 0.03͒ ⍀. Ṽ B in Si is close to the activation volume for the interstitialcy mechanism calculated for B in Si by ab initio methods. Ṽ Sb is close to some values inferred from atomistic calculations for a vacancy mechanism; problems of interpretation are discussed. A phenomenological thermodynamic treatment of diffusion under hydrostatic and nonhydrostatic stress is developed for sample configurations in which virtually all point defect equilibration occurs at the free surface of a hydrostatically or biaxially strained thin film stack. Relationships are predicted between the effects of hydrostatic and biaxial stress on diffusion normal to the surface. The prediction for Sb diffusion agrees reasonably well with measured behavior for Sb diffusion in biaxially strained Si and Si-Ge films, lending additional support to the conclusion that the vacancy mechanism dominates Sb diffusion, and supporting the nonhydrostatic thermodynamic treatment. The same analysis is used to compare hydrostatic boron results with ab initio calculations and with literature values for the biaxial strain effect on diffusion, and the resulting agreements and disagreements are discussed critically. Predictions for the effect of biaxial strain on diffusion parallel to the surface are made using these results and analyses.
On the incorporation of Mg and the role of oxygen, silicon, and hydrogen in GaN prepared by reactive molecular beam epitaxy
The diffusivity of B in Si is enhanced by pressure, characterized by an activation volume of V*=−0.17±0.01 times the atomic volume; V* is close to the formation volume of the self-interstitial determined by atomistic calculations. The results for hydrostatic pressure are used to make predictions for the effect of biaxial strain on diffusion. Assuming an interstitial-based mechanism and a range of values for the anisotropy in the migration volume, comparison is made between our results, the atomistic calculations, and the measured dependence of B diffusion on biaxial strain. We find a qualitative consistency for an interstitial-based mechanism with the measured strain effect on diffusion in Si–Ge alloys, but not with the measured strain effect in pure Si. Experiments and calculations to determine the origin of this discrepancy are discussed.
A high-temperature pressure calibration technique using Sm-doped Y 3 Al 5 O 12 ͑Sm:YAG͒ crystal as the pressure calibrant has been developed by studying its Y1 through Y10 fluorescence peaks ͑frequencies from 15 600 to 17 200 cm Ϫ1 ͒ at pressures ͑p͒ from 1 bar to 19 GPa and temperatures ͑T͒ from 20 to 850°C in externally heated diamond anvil cells. The entire spectrum was fit to a sum of ten Lorentzians plus a linear background. The positions, relative intensities and widths were represented by empirical functions of p and T. Several fitting routines for p determination were created based on these dependences, and were tested on various high-p and high-T experimental Sm:YAG fluorescence spectra. The p values obtained from the fitting routines are compared with those obtained from the ruby and the nitrogen (N 2) vibron pressure scales. A fitting routine is proposed that can determine p from 20 to 850°C within an estimated uncertainty of 0.4 GPa.
Arsenic-doped GaN films and GaNAs films have been synthesized by MOCVD. Samples were grown on sapphire, GaN-coated sapphire, and GaAs substrates. Composition, structure, and phase distribution were characterized by EPMA, SIMS, XRD, and TEM. The arsenic content increases demonstrably as the growth temperature descreases from 1030 to 700 ˚C. In the high temperature limit, high quality arsenic-doped GaN forms on GaN-coated sapphire. In the low temperature regime, nitrogen-rich GaNAs forms under some growth conditions, with a maximum arsenic mole fraction of 3%, and phase segregation in the form of GaAs precipitates occurs with an increase in arsine pressure. Preferential formation of the nitrogen-rich phase on GaN-coated sapphire suggests the presence of substrate-induced "composition pulling".
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