Float Zone Silicon Research Articles

Temperature dependence of the radiative recombination coefficient of intrinsic crystalline silicon

The radiative recombination coefficient B(T) of intrinsic crystalline silicon is determined as a function of temperature over the temperature range 77–300 K. We observe that B(T) decreases as a function of temperature and we compare our results to previously published contradictory data from the literature. The radiative recombination coefficient is calculated from the absorption coefficient for band-to-band transitions, which we determine at different temperatures from photoluminescence spectra measured on planar high resistivity float zone silicon wafers. Photoluminescence spectra could be detected over a large range of more than five orders of magnitude, which allowed us to determine extremely low values of the absorption coefficient in the spectral range where absorption processes are accompanied by the simultaneous absorption of up to four phonons.

Supergain transistors on high-purity float-zone silicon substrate

Since float-zone (FZ) silicon has lower contamination and longer minority carrier lifetime than those in Czochralski silicon and other semiconductor materials, it has potential advantages to fabricate a bipolar junction transistor on the FZ substrate to achieve high gain at very low current levels. In this report, the authors present preliminary experimental results on supergain bipolar junction transistors fabricated on unusual FZ refined high-resistivity silicon substrate and by ion implantation technology. A phosphorus-doped polycrystalline silicon backside gettering layer has been employed to preserve the long carrier lifetime of the high-purity FZ silicon. Bipolar junction transistors have demonstrated high current gain, more than 3300 for ultralow base current levels of 10 pA in this study. Possible applications of high-purity FZ silicon on some advanced semiconductor devices and circuits are discussed in this letter.

High-gain bipolar detector on float-zone silicon

Since the float-zone (FZ) silicon has lower contaminations and longer minority-carrier lifetime than those in Czochralski silicon and other semiconductor materials, it has potential advantages to fabricate bipolar detectors on the high-purity FZ silicon substrate to achieve a high gain at ultra-low-signal levels. The authors present preliminary experimental results on a bipolar detector fabricated on an unusual high-purity FZ silicon substrate. A backside gettering layer of phosphorus-doped polysilicon was employed to preserve the long carrier lifetime of the high-purity FZ silicon. The device has been investigated in the detection of a continuous flux of X-ray and infrared light. The bipolar detector with a circular emitter of 2 mm diameter has demonstrated high gains up to 3820 for 22 keV X-ray from a 1 mCi Cd radioactive source (the X-ray photon flux, received by the detector is estimated to be ∼7.77×10 4/s). High gain up to 4400 for 0.17 nW light with a wavelength of 0.83 μm has been observed for the same device.

Deep Levels in Oxygenated n-Type High-Resistivity FZ Silicon before and after a Low-Temperature Hydrogenation Step

The behavior of oxygen in oxygen-doped high-resistivity (HR) n-type float-zone (FZ) silicon has been studied using a combination of analytical techniques. In the as-doped material, a large number of deep levels have been observed with deep-level transient spectroscopy. The corresponding parameters (concentration, activation energy, and trap signature) are given, and the possible identity is discussed in view of the presence of oxygen and other impurities in the material. In addition, the impact of a low-temperature hydrogen-plasma preannealing on the formation of oxygen thermal donors (OTDs) and other oxygen-related shallow thermal donors (STDs) at 450°C is described. It is shown that the introduction rate of OTDs in oxygenated HR FZ silicon is much smaller than in Czochralski silicon. In fact, for short anneals at 450°C following a plasma treatment, the STDs are the ones which have been predominantly created near the surface of the samples. © 2003 The Electrochemical Society. All rights reserved.

Radiation damage in silicon detectors

Radiation damage effects in silicon detectors under severe hadron and gamma-irradiation are surveyed, focusing on bulk effects. Both macroscopic detector properties (reverse current, depletion voltage and charge collection) as also the underlying microscopic defect generation are covered. Basic results are taken from the work done in the CERN-RD48 (ROSE) collaboration updated by results of recent work. Preliminary studies on the use of dimerized float zone and Czochralski silicon as detector material show possible benefits. An essential progress in the understanding of the radiation-induced detector deterioration had recently been achieved in gamma irradiation, directly correlating defect analysis data with the macroscopic detector performance.

Annealing study of oxygenated and non-oxygenated float zone silicon irradiated with [formula omitted] protons

Introducing oxygen into the silicon material is believed to improve the radiation hardness of silicon detectors. In this study, oxygenated and non-oxygenated silicon samples were processed and irradiated with 15 MeV protons. In order to speed up the defect reactions after the exposure to particle radiation, the samples were heat treated at elevated temperatures. In this way, the long-term stability of silicon detectors in hostile radiation environment could be estimated. Current–voltage measurements and Surface Photovoltage (SPV) method were used to characterize the samples.

'Six-beam X-ray section topograph' images and computer-simulated images using the new n-beam dynamical theory based on the Takagi-Taupin equations.

A 'six-beam X-ray section topograph' experiment was performed whose images are in excellent agreement with the images computer-simulated using the theory derived by one of the authors [Okitsu (2003). Acta Cryst. A59, 235-244] based on the Takagi-Taupin dynamical theory. X-rays whose wavefront was limited to 0.1 x 0.1 mm were incident on a [1 1; 1]-oriented floating-zone silicon crystal with thickness of 9.911 mm so that a six-beam condition was satisfied. The six reflection indices were 000 (forward diffraction), 440, 484, 088, 4;48 and 4;04. The plane of incidence of the 088 reflection was adjusted so as to be perpendicular to the direction of the incident horizontal linear polarization of the synchrotron radiation, which was monochromated into 18.5 keV (0.670 A wavelength). While the simulations were performed under the assumptions that the incident X-rays were linearly polarized both horizontally and vertically, they were evidently different and only the simulated images under the assumption of horizontally polarized incident X-rays were in excellent agreement with the images obtained by the experiment.

Modelling of phase boundaries for large industrial FZ silicon crystal growth with the needle-eye technique

In order to facilitate the numerical calculations of the phase boundaries in large industrial floating zone silicon crystal growth with the needle-eye technique, the chain of improved mathematical models is developed. The phase boundaries are solved in a partly transient way and the modelling improvements cover the open melting front, the inner triple point and the free melt surface. The view factors model is applied for the radiative heat transfer. The electromagnetic field is calculated with account of a multiple-slit inductor.

Spin-dependent recombination electron paramagnetic resonance spectroscopy of defects in irradiated silicon detectors

Spin-dependent recombination (SDR) electron paramagnetic resonance (EPR) spectroscopy is applied for investigation of paramagnetic recombination centers in irradiated silicon p−n junction detectors (diodes) formed on float-zone (FZ) silicon wafers. The main radiation defects, associated with SRD-EPR spectra arising from excited triplet states, are assigned to complexes of two substitutional carbon atoms and one interstitial silicon atom (CS+SiI+CS) and to oxygen + vacancy (O+V) complexes (A-centers). In spite of the low concentration of oxygen in FZ silicon the A-centers are found to play an important role in the recombination process in the diodes. At temperatures T<100 K the SDR-EPR spectra are well observable by measurements of the microwave conductivity or by detecting a dc forward current IF below a forward-blocking voltage UFBL. At UFBL the IF has a steep jump followed by a decrease of the voltage over the diode and a negative resistance region with oscillations of the current. The SDR-EPR spectrum arising from the (CS+SiI+CS) complexes was found to decrease strongly in the forward biased diodes. This effect can be attributed to coexistence of two different configurations of the carbon related defect in the bulk n-type region of the diodes.

Characterisation of oxygen and oxygen-related defects in highly- and lowly-doped silicon

In this paper, an overview will be given about analytical techniques which are suitable for the study of oxygen and oxygen precipitation in highly- and lowly-doped silicon. It will be shown that in the case of highly-doped silicon, the application of Fourier Transform Infrared (FT-IR) absorption spectroscopy requires the use of ultra-thinned or high-fluence irradiated samples and a dedicated data analysis. This sample preparation is necessary to reduce the free carrier absorption in the mid-IR region. It is shown that besides the interstitial oxygen concentration [O i] and the amount of precipitated oxygen, it is possible to determine the stoichiometry of oxygen precipitates from the study of the corresponding absorption bands. Oxygen precipitation in p + silicon can also be investigated by the D1–D2 lines in photoluminescence (PL) on as-grown or heat–treated material without special sample preparation. In oxygen-doped high-resistivity float-zone silicon, standard FT-IR analysis can be applied to determine [O i]. The presence of oxygen-related shallow donors can be probed by a combination of electrical (spreading resistance probe, SRP; capacitance–voltage, C– V) and (quasi-)spectroscopic techniques (deep-level transient spectroscopy, DLTS).

The application of platinum–silicide anode layer to decrease the static and turn-off losses in high-power P-i-N diode

The platinum–silicide layer was investigated as the anode contact of a high-power P-i-N diode. The thermal stability at 700 °C was found sufficient for the purpose of Pt in-diffusion from the platinum–silicide layer into the volume. The diffusion, which was controlled using the radiation defects resulting from the 10 MeV alpha particle irradiation, represents a new local lifetime control in the float zone silicon with very low-leakage current, while keeping the benefits of traditional approaches.

Flux-enhanced monochromator by ultrasound excitation of annealed Czochralski-grown silicon crystals

The neutron flux from monochromator crystals can be increased by ultrasound excitation or by strain fields. Rocking curves of both a perfect float-zone silicon crystal and an annealed Czochralski silicon crystal with oxygen precipitates were measured at various levels of ultrasound excitation on a cold-neutron backscattering spectrometer. We find that the effects of the dynamic strain field from the ultrasound and the static strain field from the defects are not additive. Rocking curves were also taken at different ultrasound frequencies near resonance of the crystal/ultrasound-transducer system with a time resolution of 1 min. Pronounced effects of crystal heating are observed, which render the conditions for maximum neutron reflectivity delicate.

Surface passivation of crystalline silicon by Cat-CVD amorphous and nanocrystalline thin silicon films

In this work, we study the electronic surface passivation of crystalline silicon with intrinsic thin silicon films deposited by Catalytic CVD. The contactless method used to determine the effective surface recombination velocity was the quasi-steady-state photoconductance technique. Hydrogenated amorphous and nanocrystalline silicon films were evaluated as passivating layers on n- and p-type float zone silicon wafers. The best results were obtained with amorphous silicon films, which allowed effective surface recombination velocities as low as 60 and 130 cm s −1 on p- and n-type silicon, respectively. To our knowledge, these are the best results ever reported with intrinsic amorphous silicon films deposited by Catalytic CVD. The passivating properties of nanocrystalline silicon films strongly depended on the deposition conditions, especially on the filament temperature. Samples grown at lower filament temperatures (1600 °C) allowed effective surface recombination velocities of 450 and 600 cm s −1 on n- and p-type silicon.

Second-order generation of point defects in gamma-irradiated float-zone silicon, an explanation for “type inversion”

Radiation-induced defects in silicon diodes were investigated after exposure to high doses of Co60-gamma irradiation using the thermally stimulated current method. We have found that, for high irradiation doses, a second-order defect can be detected. This defect is largely suppressed in oxygen-enriched material while it is the main cause for the space charge sign inversion effect observed in standard float-zone material.

Radiation defect distribution in silicon irradiated with 600 keV electrons

Low-doped n-type float zone silicon was irradiated with 600 keV electrons to fluences from 2×10 13 to 1×10 15 cm −2. Radiation defects, their introduction rates and full-depth profiles were measured by two complementary methods – the capacitance deep level spectroscopy and the high-voltage current transient spectroscopy. Results show that, in the vicinity of the anode junction, the profile of vacancy-related defect centers is strongly influenced by electric field and an excessive generation of vacancies. In the bulk, the slope of the profile can be derived from the distribution of absorbed dose taking into the account the threshold energy necessary for Frenkel pair formation and the dependency of the defect introduction rate on electron energy.

Silicon vacancy containing two hydrogen atoms studied with electron paramagnetic resonance and infrared absorption spectroscopy

Float-zone and Czochralski-grown silicon crystals have been implanted with protons or deuterons. Electron-paramagnetic-resonance measurements performed during illumination with light at 1064 nm reveal a signal, labeled $\mathrm{DK}5,$ in addition to the well-known signal from ${\mathrm{VO}}^{*}$---the excited spin-triplet state of the oxygen-vacancy defect. The $\mathrm{DK}5$ signal originates from a spin-triplet state of a vacancy-type defect with monoclinic-I (near-orthorhombic-I) symmetry. In contrast to the ${\mathrm{VO}}^{*}$ signal, $\mathrm{DK}5$ has about the same intensity in the spectra recorded on oxygen-lean and oxygen-rich samples, which indicates that the $\mathrm{DK}5$ defect is not oxygen related. However, the close resemblance between the D tensors of $\mathrm{DK}5$ and ${\mathrm{VO}}^{*}$ strongly suggests that the electron-spin distributions are similar in the two defects. Moreover, anisotropic hyperfine splittings from two proton spins are partially resolved in the $\mathrm{DK}5$ signal. The signal is assigned to ${\mathrm{VH}}_{2}^{*},$ the excited spin-triplet state of the silicon vacancy containing two hydrogen atoms, which is the simplest defect consistent with the observed properties. The isochronal annealing behavior of $\mathrm{DK}5$ coincides with that of two infrared-absorption lines at 2063 and 2077 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, which, like $\mathrm{DK}5,$ are observable only during illumination. These lines are assigned to Si-H stretch modes of ${\mathrm{VH}}_{2}^{*}.$

Properties of an Iron–Vacancy Pair in Silicon

The peculiarities of formation and annealing, and energy level position of an iron–vacancy (FeV) pair in silicon were investigated using electron-spin resonance (ESR) and photo-ESR methods. The pairs are created in iron-doped float-zone grown silicon samples during electron-irradiation and survive annealing treatment at temperatures of 400–500°C. Results of a photo-ESR study suggest that FeV in silicon is a hole trap with an energy level positioned at about 0.51 eV above the valence band. The complexes of a vacancy and two iron atoms (2FeV) are less stable than the FeV pairs and anneal out at 300–350°C in the same samples.

The effect of oxygenation on the radiation hardness of silicon studied by surface photovoltage method

The effect of oxygenation on the radiation hardness of silicon detectors was studied. Oxygen-enriched and standard float-zone silicon pin-diodes and oxidized samples were processed and irradiated with 15-MeV protons. After the irradiations, the surface photovoltage (SPV) method was applied to extract minority carrier diffusion lengths of the silicon samples. Adding oxygen to silicon was found to improve the radiation hardness of silicon. The effect was visible in minority carrier diffusion lengths as well as in reverse bias leakage currents. The suitability of SPV method for characterizing irradiated silicon samples was proved.

Identification of hydrogen related defects in proton implanted float-zone silicon

Hydrogen related defects in high purity n-type float zone silicon samples have been studied by means of Deep Level Transient Spectroscopy. They were introduced, as well as the characteristic vacancy-oxygen (VO) and divacancy (V 2 ) centers, by MeV proton implantation. Two hydrogen related defect levels were resolved at 0.32 eV and 0.45 eV below the conduction band edge (E c ). Careful annealing studies indicate strongly that a third hydrogen related level, overlapping with the singly negative charge state level of V 2 , is also present in the implanted samples. The annealing behavior of the hydrogen related defects has been compared with literature data leading to a rather firm identification. The E c -0.32 eV level originates from a VO center partly saturated with hydrogen (a VOH complex) while the E c -0.45 eV level may be ascribed to a complex involving a monovacancy and a hydrogen atom (a VH complex). The third hydrogen related defect is tentatively ascribed to a complex involving a hydrogen atom and a divacancy (a V 2 H complex).

Dislocation luminescence in nitrogen-doped Czochralski and float zonesilicon

This paper reports the results of a study of the effect of nitrogen on the opticalproperties of dislocations in nitrogen-doped Czochralski and nitrogen-doped floatzone silicon samples where the nitrogen doping was carried out by adding Si3N4in the molten silicon charge or by nitrogen gas dissolution. Dislocations wereintroduced by plastic deformation at 650°C. In nitrogen-doped plasticallydeformed samples, emissions in the range of the D1–D4 bands of dislocations arepresent with a significant shifting from the energies and intensities of thecorresponding bands in nitrogen-free samples. It has been shown that the maineffect of nitrogen could be the enhancement of the oxygen precipitation. Theresults confirm the suggestion of some of the present authors that luminescence at0.830 eV is associated with some intrinsic properties of oxygen precipitates.