N. A. Stolwijk

Self-diffusion in the intermetallic compound CoGa

Abstract In the ordered B2 compound CoGa, self-diffusion coefficients of both 60Co and 67Ga have been measured for five compositions, namely 60·0, 56·0, 50·0, 48·0 and 45·2 at.% Co, covering a large diffusivity range from 10−8 to 10−14 cm2/s. In addition, a small number of self-diffusion coefficients has been determined for four intermediate compositions, namely 58·0, 54·0, 52·0 and 47·0 at.% Co. The Arrhenius plots for the Co and Ga diffusion in every composition are curved and can be fitted to the sum of two exponentials: D = D 0a exp (-Q a/kT) + D 0b exp (-Q b/kT). The lower activation energies and frequency factors for Co diffusion have average values of 2·4 eV and 0·7 cm2/s respectively. This Co process has been attributed to diffusion via single vacancies and nearest-neighbour jumps. For every composition the other Co activation energy equals one of the Ga activation energies, within error limits, at values of about 3·1 eV. The associated Co frequency factors are of the order of 1000 cm2/s and the C...

Diffusion of gold in dislocation-free or highly dislocated silicon measured by the spreading-resistance technique

The diffusion of Au in dislocation-free or plastically deformed Si (1011 to 1013 dislocations/m2) was measured with the aid of the spreading-resistance technique. The Au profiles produced indislocation-free Si slices by in-diffusion from both surfaces possess nonerfc-type U shapes as predicted by the so-called kick-out diffusion model. This model is used to calculate the contribution of self-interstitials to the (uncorrelated) Si self-diffusion coefficient,DISD=0.064×exp(−4.80 eV/kT)m2 s−1, from the present and previous data on the diffusivity and solubility of Au in Si in the temperature range 1073–1473 K. Inhighly dislocated Si the diffusion of Au is considerably faster than in dislocation-free Si. From the erfc-type penetration profiles found in this case, effective Au diffusion coefficients were deduced and combined with data on the solubility of Au in Si. ThusCieqDi=0.0064 ×exp(−3.93 eV/kT)m2 s−1 was obtained in the temperature range 1180–1427 K, whereCieq andDi are the solubility and diffusivity of interstitial Au in Si.

Diffusion of gold in silicon studied by means of neutron-activation analysis and spreading-resistance measurements

In- and out-diffusion of gold in silicon were investigated with the aid of a neutronactivation analysis in combination with mechanical sectioning or by the spreadingresistance technique. In-diffusion profiles in the range 1371–1073 K show that Au diffuses in Si mainly via the so-called kick-out mechanism. From the Au diffusion and solubility measurements the interstitialcy contributionDISD to the Si self-diffusion coefficient was determined, which shows that the self-diffusion occurs to a considerable extent via selfinterstitials. Out-diffusion profiles at 1173 K were measured on wafers homogeneously supersaturated with Au. The observed decrease of the electrical activity of Au in the bulk indicates that during the out-diffusion anneal the majority of Au atoms originally dissolved substitutionally changes its configuration.

Diffusion and solubility of copper in germanium

Diffusion profiles and the solubility of Cu in Ge were measured in the temperature interval 850–1200 K by means of the spreading‐resistance technique. From these data it is concluded that the diffusion of Cu in Ge involves the interchange between a highly mobile interstitial configuration, Cui, and a practically immobile substitutional configuration, Cus, with the aid of vacancies, V, via the so‐called dissociative mechanism, Cui+V⇄Cus. The excellent agreement of the values of the vacancy contribution to the tracer self‐diffusion coefficient in Ge, as calculated from our diffusivity and solubility data on Cu in Ge, with directly measured values of the 71Ge tracer self‐diffusion coefficient from the literature demonstrates that self‐diffusion in Ge occurs via vacancies. A comparison with the mechanisms of Au and self‐diffusion in Si is presented.

Diffusion of boron in silicon carbide: Evidence for the kick-out mechanism

We report diffusion experiments of implanted boron (B) in nitrogen-doped 4H- and aluminum-doped 6H-SiC which were performed at temperatures between 1700 and 1800 °C. Transient enhanced B diffusion caused by implantation damage was effectively suppressed by annealing of the B-implanted samples at 900 °C prior to the diffusion anneal. Concentration profiles of B measured with secondary ion mass spectrometry are accurately described on the basis of the kick-out mechanism. This provides strong evidence that Si self-interstitials mainly mediate B diffusion.

Double-hump diffusion profiles of copper and nickel in germanium wafers yielding vacancy-related information

Diffusion of Cu and Ni into Ge was investigated between 700 and 900 °C with the aid of rapid isothermal lamp annealing and spreading-resistance profiling. Using low-dislocation-density single-crystal Ge wafers with a backside gold layer, we observed typical double-hump diffusion profiles of both Cu and Ni. These profiles can be described within the dissociative model by taking into account that the front surface acts as source for both vacancies (V) and Cu or Ni while the back surface combines the V-source feature with a Cu, Ni-sink property. Profile fitting yields data regarding the V-assisted Ge self-diffusion coefficient and the equilibrium concentration of vacancies as a function of temperature.

A universal ion-beam-sputtering device for diffusion studies

An apparatus for ion-beam-sputtering is described which offers for the first time the possibility of measuring radiotracer diffusion profiles with mean diffusion length (D is the tracer diffusion coefficient and t is the diffusion time) in the nano- as well as in the micrometre range. It is also possible to use the device for ion milling, especially for the deposition of thin layers of radiotracer onto diffusion samples. Investigations of diffusion in pure metals, in a metallic glass, in a compound semiconductor and in intermetallic compounds are presented as examples.

Self‐interstitial and vacancy contributions to silicon self‐diffusion determined from the diffusion of gold in silicon

We present an analysis of gold diffusion profiles in silicon taking into account that both self‐interstitials and vacancies are present at thermal equilibrium. We find that at 1000 °C the contribution of self‐interstitials to silicon self‐diffusion is about equal to that of vacancies.

Solubility, diffusion and thermodynamic properties of silver in silicon

Concentration-depth profiles of Ag in Si have been measured with the aid of neutron activation analysis combined with serial removal of sections. The Ag diffusion appears to be very fast. In the bulk of dislocation-free Si wafers saturation is achieved after short periods of annealing. From this the authors conclude that interstitial Agi is the predominant configuration in Si without dislocations. Equilibrium concentrations of Agi are determined for temperatures between 1287 and 1598 K. The results are thermodynamically analysed, taking into account Ag-Si liquidus data. In dislocated Si much higher Ag concentrations are observed, which vary irregularly with the penetration depth. A comparison of the diffusion and solubility of Ag and Au in Si suggests that in Si with dislocations substitutional Ags may arise from Agi-Ags transitions. Finally an estimate of the Agi diffusivity is obtained.

Diffusion kinetics and isotope effects for atomic migration via divacancies and triple defects in the CsCl (B2) structure

Abstract Expressions for the diffusion coefficients and correlation factors for diffusion by means of divacancies in ionic compounds with the CsCl (B2) structure are calculated. Values for the correlation factors as a function of the ratio of the defect-atom exchange frequencies of both components are tabulated. The correlation factors are obtained in explicit form. From this it turns out that a measurement of isotope effects would yield (in principle) the values of the correlation factors. It is demonstrated that, in a measurement of diffusion coefficients, differences in jump frequencies and activation energies between both components are decreased by correlation effects. For intermetallic compounds with the triple-defect B2 structure, atomic migration via triple defects has been proposed (Stolwijk, Van Gend and Bakker 1980). Expressions for the diffusion coefficients of both components via this defect are presented and it is shown how values for the correlation factors can be deduced from the divacancy...