A comparison of hydrogen incorporation and effusion in doped crystalline silicon,germanium, and gallium arsenide

The incorporation of deuterium into crystalline silicon, germanium, and gallium arsenide from a plasma source is investigated as a function of sample temperature during the plasma treatment. The total amount of incorporated deuterium and its bonding states are characterized by the thermal effusion (TE) technique for different dopants and doping levels. In all samples investigated, we find a strong influence of the passivation temperature on these quantities; however, there are large differences between different semiconductors and for different doping levels or dopants. The results are discussed in terms of plasma-induced defects, dopant-deuterium complexes, and surface effects.Dedicated to H.-J. Queisser on the occasion of his 60th birthday     

On the nature of point defects and the effect of oxidation on substitutional dopant diffusion in silicon

An extensive analysis of the substitutional dopant diffusion phenomena in silicon during oxidation is presented. The analysis covers qualitative as well as quantitative aspects of the oxidation-enhanced and -retarded diffusion (OED and ORD) phenomena, and examines three different possible assumptions that can be made on the nature of the silicon thermal equilibrium point defect species: silicon self-interstitials (I) only, vacancies (V) only, coexistence of I and V. The only consistent way to interpret all properly documented OED/ORD data is to assume that I and V coexist under oxidation as well as under thermal equilibrium conditions at high temperatures.     

Correlations between clusterization and electrical properties within fluorite-type anions excess solid solutions: Setting of a model

We proposed a model to correlate, in a continuous manner, the composition dependence of electrical properties and the progressive extension of clusterization when the substitution rate increases in a fluoride anion excess CaF₂-type solid solution of M_1–xM _x ²⁺ F_2+x(=1,2,3). A new classification of clusters is given based on the presence or absence of coexistence between two types of interstitial fluoride ions.The second part of the paper is devoted to the representation of the sum of interstitial fluoride ionsn _{F int} and the sum of vacancies in normal sitesn according to the general equationy=(mx ³+qx)/(x ²+q). This model allows us to correlate the structural and electrical properties of a large number of solid solutions with fluorite-type structure.     

Point defects,diffusion processes,and swirl defect formation in silicon

The paper consists of three parts. In the first part we review the basic experimental and theoretical results which shaped our present knowledge on point defects and diffusion processes in silicon. These results concern on one side oxidation effects which established that silicon self-interstitials and vacancies coexist in silicon and on the other side diffusion of gold into dislocation-free silicon which allowed to determine the self-interstitial contribution to silicon self-diffusion and to estimate the corresponding vacancy contribution. In the second part we discuss topics for which an understanding is just emerging within the framework of coexisting self-interstitials and vacancies: reaching of local dynamical equilibrium between self-interstitials and vacancies; rough estimates of the thermal equilibrium concentrations of self-interstitials and vacancies and their respective diffusivities, and finally, various possibilities to generate an undersaturation of self-interstitials. In the third part we examine swirl defect formation in silicon in terms of vacancies and self-interstitials.     

Gold diffusion in silicon by Rapid Optical Annealing

Gold diffusion in silicon is investigated using Rapid Optical Annealing at temperatures in the range of 800°C to 1200°C and annealing times from 300 s down to 1 s. The resulting content of substitutional gold is determined by spreading resistance measurements and analyzed by comparison with extensive numerical simulations.The profiles obtained show a broader spectrum as compared to the U-shapes after long time diffusion. The cooling process affects the profiles significantly, since they depend on the wafer thickness. An unexpected penetration depth was found after 1200°C diffusion in thick wafers, which are subject to small cooling rates. This phenomenon is due to a special combination of reverse kick-out, deep diffusion of highly supersaturated interstitial gold, and again an incorporation in lattice sites, termed the RDI effect.Numerical calculations allow us to reproduce the experimentally observed profiles only if a sensitive balance between the different temperature dependencies is obeyed. These investigations, therefore, yield new information about the equilibrium concentration and diffusion of silicon interstitials. A best set of parameters is presented. The time constant of the kick-out process is quantified for the first time.     

Electrical activity and precipitation behavior of copper in gallium arsenide

The electrical properties and preferred lattice site of Cu in GaAs were investigated combining electrical and optical measurements with ion beam and structural analysis. From this comprehensive study it was determined that Cu introduces two levels in the band gap, that the concentration of electrically active centers introduced by Cu diffusion is considerably smaller than the total Cu concentration, that this ratio of electrically active to total Cu concentration depends strongly on the cooling speed after diffusion, and that the portion of Cu that remains electrically inactive forms Cu-Ga precipitates.     

Approximation to the two-step diffusion profile by a series of gaussian functions

The two-step diffusion profile is approximated by a series of gaussian functions. Its accuracy is dependent upon the number of terms used in the series, but independent of the number and the spacing of exact data points.     

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,D _I ^SD =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. ThusC _i ^eq D _i=0.0064 ×exp(–3.93 eV/kT)m² s^–1 was obtained in the temperature range 1180–1427 K, whereC _i ^eq andD _i 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 contributionD _I ^SD 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.     

Rapid thermal diffusion of aluminum in silicon and its interaction with phosphorus

Aluminum diffusion profiles in silicon were produced under rapid thermal processing conditions using a Si-sandwich structure to avoid losses of aluminum by reaction with the quartz reactor. The impact of phosphorus on the diffusion behaviour of aluminum was investigated by predeposition of P into Al-diffused wafers and vice versa. Dopant profiles were determined by SIMS (Secondary-Ion-Mass Spectroscopy), electrochemical CV-and SRP (Spreading Resistance) analysis. The resulting profiles after Al predeposition at 1293 K exhibit high Al-surface concentrations up to the solid solubility limit of about 2×10²⁵ m^–3. It is shown that phosphorus has a great influence on the drivein behaviour of Al, leading to an accelerated Al diffusion in front of the P profile (enhanced Al diffusion caused by self-interstitial supersaturation) and an up-hill migration of Al in the high-concentration regime, which can be explained by field-assisted diffusion. A strong retardation of aluminum diffusion combined with concentrations well above the solidsolubility limit was observed during the Al predeposition into P-diffused wafers.     

Spectroscopic investigation of oxygen vacancies in solid oxide electrolytes

The primary species in both solid-state conduction and heterogeneous electrocatalysis of solid oxide electrolytes is the anion vacancy. The nature and effect of the local environment on anion vacancies in 10 m/o yttria stabilized zirconia (YSZ) and 20 m/o erbia stabilized bismuth oxide (ESB) was studied using uv-visible absorption and fluorescence spectroscopy. Partial reduction of YSZ and ordering of the oxygen sublattice in ESB is discussed. The species common to both of these phenomena, anion vacancies, was found to be luminescent and the absorption and fluorescence spectra attributable to F-center type defects is described.Current address: Materials Research Laboratory, SRI International, 333 Ravenswood Ave., Menlo Park, CA 94025, USA     

Positron diffusion in solids and the reconstruction of inhomogeneous defect distributions from lifetime measurements

The time dependent diffusion trapping equations for positrons implanted into inhomogeneous solids are analyzed. This problem is of central importance in the study of polycrystalline materials and for the application of pulsed positron beams to defect studies in materials research. The main problem in previous investigations was the necessity to solve the time-dependent diffusion equation. It prevented analytical treatment in all but the simplest applications. For the first time this difficulty is eliminated by invoking a new concept, the observable local annihilation characteristics for local implantation of positrons into the thermalized ensemble. It will be shown that the local annihilation characteristics are governed by field equations which reduce to the well known quantities of the standard trapping model in the case of homogeneous defect distributions. Furthermore, inhomogeneous defect distributions are uniquely determined from the field equations provided the local annihilation characteristics are known. Analytical solutions are derived and applied successfully to recent experimental results for a selection of simple, but realistic problems. The formal procedure includes internal drift fields and could be extended to cover also the epithermal period of positron thermalization, if necessary.     

Two-dimensional phosphorus diffusion for soft drains in silicon MOS transistors

Phosphorus has a considerably less steep concentration profile than arsenic. Therefore phosphorus is considered as an alternative dopand for soft drain concepts in future MOS devices. In-diffusion of phosphorus starting from a high surface concentration generatesexcess point defects which diffuse into the depth of the crystal and lead to a tail in the phosphorus concentration profile by considerably enhancing the phosphorus diffusion in this region. It is also well known that the interface between silicon and a non growing oxide acts as a sink for excess point defects. Since source/drain areas of MOS transistors are surrounded by gate and isolation oxides, the question arises how the resulting excess point defect distribution may influence the lateral and vertical diffusion profile of phosphorus and hence the channel length and the junction depth of the source/drain region in a MOS device. We extended the one-dimensional Fair-Tsai model of phosphorus diffusion into two dimensions and incorporated that the interface between silicon and a gate oxide acts as a sink for excess point defects and modifies their distribution. The appropriate code was implemented in the two-dimensional process simulation program LADIS. Based on this extended model two-dimensional simulations of phosphorus drains have been performed and compared to experimental results and to results from other numerical models. It turns out that the presence of the gate oxide reduces the tail in the phosphorus concentration profile, considerably in lateral direction and less pronounced in vertical direction. Limitations of the model will be discussed in detail.     

Diffusion and solubility of zinc in dislocation-free and plastically deformed silicon crystals

Floating-zone Si crystals enclosed in quartz ampoules were exposed to Zn vapour released by an elemental diffusion source. Penetration profiles of Zn in Si were recorded using the spreading-resistance technique or neutron activation analysis. Both the erfc-type distributions observed in plastically deformed specimens and the non-erfc profiles determined on dislocationfree wafers are consistently interpreted within the framework of the kick-out model. As an implication, Si self-interstitials generated in excess by interstitial-to-substitutional transitions of in-diffusing Zn atoms annihilate not only at the surface but also at dislocations. On the other hand, dislocation-induced segregation of Zn appears to be rather minor, as revealed by transition electron microscopy. Combining the Zn incorporation rate in dislocation-free Si with solubility data from saturated specimens yields the self-interstitial contribution to the Si self-diffusion coefficient.Dedicated to H.J. Queisser on the occasion of his 60th birthday     

Calculations of vacancy formation and migration energies offcc Cs by the LMTO-method: Application to self diffusion

Vacancy formation and migration energies offcc Cs were calculated from first principles by the LMTO-method. The change in slope of the Arrhenius curve for the diffusion coefficient as a function of temperature is discussed and its occurrence is explained by vacancies concentration dependence of the energy of formation. The frequency of vibration and the jump probability of an atom were calculated and it is shown that they are direction dependent.     

High-temperature diffusion of phosphorus and boron in silicon via vacancies or via self-interstitials?

The paper re-examines the effect of oxidation on the diffusion of phosphorus and boron in silicon as well as recent results on redistribution phenomena of these dopants under irradiation and on the emitter-push effect. It is shown that at high temperatures phosphorus and boron diffuse via a defect mechanism involving silicon self-interstitials. These results support the view-point that self-interstitials are the dominating point defects in silicon under thermal equilibrium conditions. Possible generation mechanisms for the self-interstitial supersaturation causing the emitter-push effect are suggested.     

Boron neutralization and hydrogen diffusion in silicon subjected to low-energy hydrogen implantation

Using the hydrogen neutralization of the boron acceptor, the diffusion of hydrogen is investigated in the temperature range 20 °–160 °C. The hydrogenation is performed by low-energy implantation. We observe a fast initial hydrogen migration, followed by a long-time diffusion phase that is described by an effective diffusion coefficientD _eff=D _{0 eff} exp(–E _a/kT) withD _{0 eff}–cm²s^–1 andE _a=(0.83±0.05) eV. No deeper hydrogen migration is detected for implantation times longer than – 30 min. Our data are explained by the build-up of a large amount of molecular hydrogen beneath the surface, which strongly hinders the transfer of the implanted hydrogen to the bulk. The thermal reactivation kinetics of the neutralized boron show a rapid initial step followed by a longtime thermally activated second order phase, which is limited by the recombination of hydrogen into molecules.     

A Systematic investigation of the dc electrical conductivity of rare-earth doped ceria

The dc electrical conductivity of rare-earth doped ceria has been measured as a function of temperature (300–600 K) and composition (0.05–15 mol% M₂O₃) on using the complex impedance technique. Five dopants have been selected, yttrium and the lanthanides Yb, Gd, Nd, and La. For all of them, the variations of the activation energy versus dopant concentration are similar and characterized by the existence of a minimum. This peculiar property can be understood if attractive interactions between immobile dopant ions and mobile oxygen vacancies are taken into account. From an analysis of the experimental results, it is concluded that this interaction extends at least to third or fourth nearest neighbors depending on the size and the electronic configuration of the dopant ion.     

On the formation of defect clusters in neutron-irradiated Si

The formation of radiation-induced defect clusters in neutron-irradiated silicon have been studied by solving the semilinear parabolic reaction-diffusion coupled equations. It is found that most of primary displacement defects (interstitial and vacancy) would be annihilated by direct I–V recombination in an extremely short time, and a lot of divacancies would be formed meantime. In particular, the production of 4-vacancy defects is independent of the concentration of sinks and impurities in the sample, and of the energy of recoil particles. The threshold energy of vacancy cluster formation has also been investigated. The results are discussed and compared with experiment observations.     

High concentration effects of ion implanted boron in silicon

The diffusion behaviour of implanted boron in silicon was investigated using the¹⁰B(n,α)⁷ Li nuclear reaction. An anomalous behavior with a strong reduction of the diffusivity above an effective solubility limit at 1.5×10¹⁹, 6×10¹⁹, and 1.1×10²⁰ cm⁻³ was found for annealing temperatures of 800, 900, and 1,000°C, respectively.