A. N. Petukh

Hydrogen-containing donors in silicon: Centers with negative effective correlation energy

The reconstruction of shallow-level hydrogen-containing donors in Si is studied. The donors are formed by implantation of low-energy (300 keV) hydrogen ions into the experimental samples and subsequent heat treatment at 450°C. The experiments are carried out for Ag-Mo-Si Schottky diodes and diodes with a shallow (∼1 μm) p+-n junction. The concentration and distribution of the donors are determined by applying the method of C–V characteristics at a frequency of 1.2 MHz. An analysis of the temperature dependence of the equilibrium electron concentration shows that the reconstruction of the hydrogen-containing donors can be described under the assumption of recharging of a center with negative effective correlation energy (U < 0). The transformation between two equilibrium configurations of a double hydrogen donor (DB++ ↔ DA0) proceeds with the Fermi level position EF = Ec − 0.30 eV. The reconstruction of the donors from a neutral to a doubly charged state (DA0 → DB++) which is stimulated by the capture of minority carriers, is observed at room temperature.

Formation of hydrogen donors in proton-implanted epitaxial silicon

The formation of shallow hydrogen donors in epitaxial silicon implanted with 300-keV hydrogen ions has been studied at implant doses from 1013 to 6 × 1015 cm−2, using commercial Mo-Si Schottky diodes with the active base region made of epitaxial phosphorus-doped silicon 5 µ m in thickness (ρ = 1.05 and 1.8 Ω cm). The results demonstrate that, at sufficiently high implant doses (F ∼ 1015 cm−2) and temperatures from 350 to 475 °C, there are at least two types of donors, one of which exhibits bistable behavior due to the negative correlation energy of a singly ionized doubly charged donor. At ∼475°C, the bistable H donor is fully annealed, whereas the concentration of stable donors remains unchanged at temperatures from 350 to 475°C. Under fixed post-implantation heat-treatment conditions (350°, 20 min), it is the implant dose that determines which type of H donor will form: at doses in the range 1013 to 1014 cm −2, H donors of the former type are formed, and the maximum in their profile coincides with the projected ion range; implant doses from 1014 to 1015 cm−2 produce H donors of the latter type, and the peak in their profile is located closer to the irradiated surface, in the region of the highest radiation damage.

Donor Center Formation in Silicon Implanted with Hydrogen Ions

We have studied the electrical properties of Schottky diodes based on epitaxial n-Si films irradiated by low-energy (300 keV) hydrogen ions. The implantation of protons at room temperature leads to the formation of shallow donors whose concentration-depth profile coincides with that of the incorporated hydrogen. These donor centers are stable on heating up to 150°C and are completely annealed at a temperature of about 250°C. Heating above 270°C leads to the formation of well-known donor centers with a concentration more than two times that of the centers of the first type. Donors of the second type are annealed in two stages at 375–425 and 450–520°C. The nature of the donor centers of both types is related to the formation and transformation of two-dimensional hydrogen-containing defects in a radiation-damaged crystal.

Procedure for rapid spectroscopic control of the distribution of oxygen and of doping impurities in silicon ingots

Spectral dependences of the coefficients of absorption by free carriers and of multiphoton absorption by a silicon lattice in the region of the interstitial oxygen band at 5.8 μm are established. A procedure for measurement of the distribution of oxygen and alloying impurities in silicon ingots is given. The effectiveness of the spectrometers developed for controlling the segregation of impurities and nonstationary convection of the silicon melt in growing ingots by the Czochralski method is shown.

Bistability of hydrogen donors in proton-implanted GeSi alloy

Shallow hydrogen donors (H-donors) were formed in a Ge1 − xSix (x = 0.012) alloy by the implantation of low-energy protons followed by heat treatment at 275°C The electrical properties of these donors have been studied using the method of capacitance-voltage characteristics. It is established that a certain fraction of the H-donors exhibit bistability, whereby their concentration changes reversibly when the sample temperature is cycled within 100–200°C. The properties of reversible H-donors in germanium are analogous to those of the bistable H-donors in silicon.

Formation of donors in germanium–silicon alloys implanted with hydrogen ions with different energies

The distributions of hydrogen-containing donors in Ge1–xSix (0 ≤ x ≤ 0.06) alloys implanted with hydrogen ions with an energy of 200 and 300 keV and a dose of 1 × 1015 cm–2 are studied. It is established that, at the higher ion energy, the limiting donor concentration after postimplantation heat treatment (275°C) is attained within ~30 min and, at the lower energy, within ~320 min. In contrast to donors formed near the surface, a portion of hydrogen-containing donors formed upon the implantation of ions with the higher energy possess the property of bistability. The limiting donor concentration is independent of the ion energy, but decreases from 1.3 × 1016 to 1.5 × 1015 cm–3, as the Si impurity content in the alloy is increased from x = 0.008 to x = 0.062. It is inferred that the observed differences arise from the participation of the surface in the donor formation process, since the surface significantly influences defect-formation processes involving radiation-induced defects, whose generation accompanies implantation.

Formation kinetics of various types of hydrogen-related donors in proton-implanted silicon

The method of C-V characteristics has been used to study the accumulation kinetics of double and shallow hydrogen-related donors in proton-implanted epitaxial silicon. It is shown that the kinetics corresponds to the first-order reactions. The activation energies ΔE1 = 2.3 eV and ΔE2 = 1.4 eV and the pre-exponential factors τ01 = 9.1 × 10−17 s and τ02 = 4.2 × 10−9 s were determined for both types of the donors, respectively. It was shown that the bistability of the electric properties of silicon is due to the double hydrogen-related donor.

New hydrogen donors in germanium

The electrical properties of n-type germanium single crystals irradiated with protons were studied by measuring capacitance-voltage characteristics. The thermal treatment of irradiated samples at 200–300°C leads to the formation of highly mobile shallow donor centers. The coefficient of diffusion of these donors is equal to that of atomic hydrogen with allowance for capture on traps. It is concluded that atomic hydrogen plays the role of a shallow donor in germanium.

Nature of large-scale oscillations in oxygen concentration along the growth axis in Czochralski-grown silicon crystals

Oxygen distribution in a Si crystal (100 mm in diameter) has been studied by the absorption method in the range of the absorption band of interstitial oxygen, λ = 5.81 μm. Large-scale fluctuations (∼1 cm) of the oxygen concentration (N0) along the growth axis were determined. Depending on the melt height, the regions of the chaotic and quasiperiodic changes were established, as well as the region of the constant N0 value, and their relation to turbulent, quasiperiodic, and stationary modes of melt convection in crystallization. The values of the critical Rayleigh number for the melt transition from stationary to quasiperiodic (3 × 103) and from quasiperiodic to turbulent (1.7 × 104) convection modes are determined for growth of silicon crystals by the Czochralski method. The dominating modes of N0 concentration oscillations at two incommensurable frequencies, f1 = 1.3 × 10−3 and f2 = 6 × 10−4 Hz, are assumed to be related to the oscillatory transfer of oxygen from the walls of the quartz crucible to the crystallization front and restructurization of the convective flow pattern of the melt in the course of crystal growth.

Identification of 4-phonon absorption bands in silicon crystals

An investigation is made of the IR absorption on silicon samples of large thickness grown by the zone-melting and pulling methods. New low-intensity bands at 1580, 1780, and 1920 cm−1 are derected. A comparison of the spectral position of the bands with the frequency of phonons allows the observed bands to be assigned to the 4-phonon transitions in the silicon lattice. A spectral dependence of the multiphonon absorption coefficient is obtained that gives a good description of the phonon absorption of silicon in the region of the 1720 cm−1 band of interstitial oxygen.