Thermal Donors In Silicon Research Articles

Electrical and Optical Characterization of Thermal Donors in Silicon

Electrical and Optical Characterization of Thermal Donors in Silicon

Oxygen Endor of Thermal Donors in Silicon

Oxygen Endor of Thermal Donors in Silicon

Evidence for an Inhomogeneous Distribution of Thermal Donors in Silicon from Electrical and Optical Measurements

Evidence for an Inhomogeneous Distribution of Thermal Donors in Silicon from Electrical and Optical Measurements

The effect of pre-heat-treatments on the formation kinetics of thermal donors in silicon

Results on the influence of different pre-heat treatments of CzSi samples on the formation of thermal donors at 450°C are given. They show that there is no influence on the thermal donor formation kinetics for most of the samples used. The time dependence of thermal donor formation can be described by Ntd(t) = Ntd, max(1 – exp (–kt)) with k = (6.2 ± 0.6) × 10−6 s−1 independent of the pre-heat treatments used. Decreases in Ntd(t) and Ntd, max caused by pre-heat treatments can be explained by decreases in [Oi] or by agglomeration of oxygen during the pre-heat treatments. It is concluded that thermal donor formation is a process with homogeneous nucleation. In Si samples with concentrations of heterogeneous nuclei such as carbon comparable with [Oi]0 the thermal donor formation kinetics can be modified by agglomeration of Oi on these nuclei occuring during both pre-heat treatment and thermal donor formation. Es werden Ergebnisse über den Einfluß verschiedenartiger Wärmevorbehandlungen von Czochralski-Si-Proben auf die Bildung von Thermodonatoren bei 450°C mitgeteilt. Es wird gezeigt, daß für die meisten Proben kein Einfluß von Wärmevorbehandlungen auf die Thermodonatorbildung besteht. Unabhängig von der Vorbehandlung kann die Zeitabhängigkeit der Thermodonator-Konzentration durch Ntd(t) = Ntd, max(1 – exp (– kt)) mit k = (6,2 ± 0,6) × 10−6 s−1 beschrieben werden. Verringerte Ntd(t) und Ntd, max nach vorhergehenden Wärmebehandlungen werden durch die Abnahme von [Oi] durch Präzipitation bzw. durch die Agglomeration von Sauerstoff infolge dieser Vorbehandlungen erklärt. Es wird geschlußfolgert, daß die Thermodonatorbildung ein Prozeß mit homogener Keimbildung ist. In Si-Proben mit heterogenen Keimen, deren Konzentration vergleichbar ist mit denen von [Oi]0 kann die Thermodonatorbildung modifiziert sein infolge der Agglomeration von Oi an diesen Keimen sowohl während der Vorbehandlung als auch während der 450°C-Wärmebehandlung.

Thermal donors in silicon: oxygen clusters or self-interstitial aggregates

There is a long-standing view that small aggregates of oxygen impurities in silicon produced by heat treatments at 450 degrees C are the defects that act as thermal donors. Recently it has been established that these treatments also lead to the generation of self-interstitials. It is now suggested that small aggregates of these intrinsic defects should alternately be considered as the complexes giving the donor properties.

On the Core of the Thermal Donors in Silicon

On the Core of the Thermal Donors in Silicon

Electronic structure of the Si:O4 complex as related to the thermal donors in silicon

Rigorous self-consistent electronic structure calculations were carried out for complexes containing four interstitial oxygen atoms in silicon. The isolated tetrahedral site interstitial oxygen impurity was also investigated and the results were correlated to the complexes formation. Our calculations indicate that four oxygen impurities in Td symmetry surrounding a silicon atom at the regular lattice site are deep acceptor centers. It is also found that distortions which drive the complex to one of the observed symmetries, D2d, remove the impurity levels from the gap. Therefore, we conclude that these complexes do not show thermal donor actions in silicon as has been suggested.

Difference in the IR absorption of thermal donors in n-Si and p-Si

The low-temperature thermal donors in silicon are currently an object of investigation; however, their nature has not been reliably established. The presence of such thermal donors in silicon with concentrations N /SUB d/ 10 U cm T results in the appearance of specific bands in the IR absorption spectrum. These bands are attributed to the photoexcitation of electrons found in the levels of the thermal donors. However, according to current theories, such absorption is possible in samples of p-Si only under the conditions of additional optical pumping, which provides for the nonequilibrium filling of the energy levels of the thermal donors. This paper is devoted to a systematic investigation of the absorption by thermal donors in n-Si and p-Si subjected to isothermal heat treatment at a temperature of 450C for various time periods. In particular an attempt is made to evaluate the validity of the interpretation of the absorption by thermal donors in p-Si as proposed by Pajot et. al.

Energy Levels and Capture Cross-Sections of Thermal Donors in Silicon

ABSTRACTThe electrical properties of thermal donors centers, generated after annealing CZ-silicon at 450° C are carefully evaluated. The energy levels are corrected for the Poole-Frenkel lowering are compared to the ionization energy of the dominant centers revealed by infrared absorption experiments. The capture cross sections are found to be ≈ 2 × 10-12 cm2 for TDI and ≈ 2 × 10-13 cm2 for TD2. Detailed examination of their temperature dependence reveals that they follow a common law σ α T-5.

The Study of Oxygen Thermal Donors in Silicon by Photothermal Ionisation Spectroscopy

ABSTRACTIt is well known that Czochralski-grown silicon contains up to 2×1018 cm-3 oxygen atoms. When this silicon is annealed at 450°C a series of “thermal” donors are formed. In this work we present the results of a study of annealed Czcochralski-silicon samples by Photothermal Ionisation Spectroscopy and IR transmission measurements. All previously reported thermal donors, which occur in the spectral region above 330cm-1, and hove ionisation energies 53–69.3 meV, are observed by us. Also, our experimental results show the presence of at least three previously unreported thermally formed donor transition series below 330cm-1. Our results indicate that the ionisation energies of these new shallow thermal donors would be 36.3, 37.0 and 37.4 meV. Assignments are made by comparison of the energy differences between excited states to those predicted by the Effective Mass Theory.

Identity of the Nl8 Epr Spectrum with Thermal Donors in Silicon+

AbstractThe effect of uniaxial stress on the NL8 EPR spectrum in 450°C heattreated silicon containing thermal donors (TD's) is described. Changes in the relative amplitudes of the NL8 spectral components are interpreted as arising from electronic redistribution between the differently oriented defects. These changes are consistent in sign and magnitude with those predicted for TD+ from observed stress effects on the TD IR and DLTS spectra.

Oxygen Precipitation and Thermal Donors in Silicon

ABSTRACTOxygen in silicon precipitates with second order kinetics at the normal diffusion rate at 450° C and there Is evidence for self-Interstitial generation. These findings are discussed In relation to thermal donors.

Formation Kinetics of Thermal Donors in Silicon

ABSTRACTThe kinetics of thermal donor formation in Czochralski-silicon at ca. 450° C are explained by a simple model based on the work of Suezawa and Sumino which derives forward and reverse reaction rates for each electrically active species from the general features of the infrared electronic absorption spectra. The model, which is independent of the chemical nature of the thermal donor core, assumes that all thermal donors beyond the first donor species are chemically stable at the donor formation temperature, and approximates the reactions for species smaller than the first thermal donor as being in chemical equilibrium. The model is shown to be consistent with both sets of the available IR spectra of thermal donors (Oeder-Wagner and Suezawa-Sumino) when differences in the annealing temperature and initial oxygen concentration are taken into account.

New Optical Transition at Thermal Donors in Silicon

ABSTRACTWe detect new luminescence lines in Czochralski-grown silicon after prolonged heat treatments at 450°C. The properties of the new optical transition are well explained by a thermal donor-free hole recombination. From the IR-absorption spectra measured on the same samples, we have evidence for an inhomogeneous distribution of the thermal donors. The spatial fluctuations of the thermal donors appear to be necessary for the new luminescence spectrum to emerge.

United model for formation kinetics of oxygen thermal donors in silicon

A new model is proposed for the formation and decay kinetics of the thermal donors in silicon. This model is an extension of the Kaiser-Frisch-Reiss (KFR) model [Phys. Rev. 112, 1546 (1958)] and includes the effect of the electronic environment hitherto neglected. The concentration of the thermal donors ${n}_{\mathrm{TD}}(t)$ is expressed by ${n}_{\mathrm{TD}}(t)=(\frac{a}{b}){[{\mathrm{O}}_{i}]}^{3}{n}^{\ensuremath{-}2}{1\ensuremath{-}\mathrm{exp}(\ensuremath{-}b{D}_{i}[{\mathrm{O}}_{i}]t)}$, where [${\mathrm{O}}_{i}$] denotes the initial oxygen-interstitial concentration; $n$, the electron concentration; ${D}_{i}$, the diffusion coefficient of oxygen interstitials; and $a$ and $b$, constants. Based on this equation, the maximum concentration ${[{n}_{\mathrm{TD}}(t=\ensuremath{\infty})]}_{\mathrm{eq}}$ and initial formation rate ${[\frac{d{n}_{\mathrm{TD}}(t)}{\mathrm{dt}}]}_{t=0}$ are expressed, respectively, by ${[{n}_{\mathrm{TD}}(t=\ensuremath{\infty})]}_{\mathrm{eq}}=(\frac{a}{b}){[{\mathrm{O}}_{i}]}^{3}{n}^{\ensuremath{-}2}$ and ${[\frac{d{n}_{\mathrm{TD}}(t)}{\mathrm{dt}}]}_{t=0}=a{D}_{i}{[{\mathrm{O}}_{i}]}^{4}{n}^{\ensuremath{-}2}$. The equations are used to derive the annealing-temperature and dopant-concentration dependences as well as the oxygen-concentration dependence of thermal-donor formation. Enhancement of the thermal donor formation in heavily doped, $p$-type materials and its suppression in heavily doped, $n$-type materials are theoretically deduced and the latter is experimentally confirmed by deep-level transient (capacitance) spectroscopy (DLTS). It is found that the aggregates with four oxygen atoms are doubly charged donors. It is further suggested that the early aggregates with two or three oxygen atoms would be doubly charged donors and would play the role of the predominant thermal donors in the initial formation stage at a temperature lower than 450\ifmmode^\circ\else\textdegree\fi{}C.

Kinetics of thermal donor generation in silicon

The generation kinetics of thermal donors at 450 °C in Czochralski-grown silicon was found to be altered by high-temperature preannealing (e.g., 1100 °C for 30 min). Thus, when compared with as-grown Si, high-temperature preannealed material exhibits a smaller concentration of generated thermal donors and a faster thermal donor saturation. A unified mechanism of nucleation and oxygen diffusion-controlled growth (based on solid-state phase transformation theory) is proposed to account for generation kinetics of thermal donors at 450 °C, in as-grown and high-temperature preannealed Czochralski silicon crystals. This mechanism is consistent with the main features of the models which have been proposed to explain the formation of oxygen thermal donors in silicon.

Oxygen-related thermal donors in silicon: A new structural and kinetic model

A structural model for the oxygen-related thermal donors produced at moderate temperatures (<500 °C) is presented, where electrical activity commences with clusters containing five or more oxygen atoms and arises from a silicon atom at the center of the cluster. The donor activity of a cluster is terminated upon the ejection of this central silicon atom in order to bring about stress relaxation. A large number of electrically active donor species are predicted, differing only in the number of oxygen atoms each species contains. This structural model satisfies the stringent symmetry requirements of electron paramagnetic resonance (EPR), explains the lack of hyperfine interaction with Si29 or O17 nuclei and the large multiplicity in the number of donor species observed by infrared spectroscopy and EPR. The proposed clusters are shown to be embryonic forms of the much larger rodlike defects examined in detail by electron microscopy. Chemical reaction theory is used to deduce the kinetic consequences of the structural model. Both approximate analytic and numerical solutions of the resulting coupled, nonlinear equations are presented. The numerical results provide a good description of the detailed infrared kinetic data on the growth of the individual donor species and, in addition, reproduce the well-known average kinetic data from resistivity measurements. In order to explain the dependence of the oxgyen diffusivity on the sample thermal history and the well-known diffusivity enhancement, a highly mobile oxygen-silicon interstitial complex is proposed, which provides a satisfactory description of the results of dichroic recovery experiments. It is shown, however, that the values of diffusivity deduced from donor formation studies are, in addition, strongly influenced by inhomogeneities in the oxygen distribution as well as by the presence of small, electrically inactive oxygen clusters prior to the anneal. It seems necessary to consider all these possibilities to explain the experimental data.

Oxygen diffusion and thermal donor formation in silicon

The information available on the diffusion of oxygen and on the formation of thermal donors in silicon is critically reviewed. In this context the effects of intrinsic point defects on the diffusion-controlled growth of oxygen precipitates is investigated in some detail. Seemingly contradictory experimental results on the diffusivity of oxygen in silicon at temperatures around 400° C are explained in terms offast-diffusing gas-like molecular oxygen in silicon. The concept of molecular oxygen is also invoked in a newly suggested model of thermal donor formation in silicon. The diffusivity of molecular oxygen in silicon is estimated to be around 10−9cm2s−1 at 450° C, almost nine orders of magnitude higher than the diffusivity of atomic oxygen in interstitial position.

Infrared-Absorption of Thermal Donors in Silicon

ABSTRACTThermal donors generated in CZ-silicon by annealing at 450° C are investigated by infrared absorption spectroscopy.Up to nine double-donors can be distinguished due to their line spectra characteristic for effective-mass-like donors.Their number and their concentrations depend on the duration of the thermal treatment. The formation of the different donors is ruled by complicated kinetics.