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The diffusion profiles of the concentration of electrically active and total concentrations of the magnesium impurity in silicon are measured. Diffusion is carried out by the sandwich method into FZ dislocation-free n-type silicon at the temperatures Tdiff = 1000 and 1100°C, and at a process duration from 0.5 to 22.5 h. The concentration profiles $${{N}_{{{\text{M}}{{{\text{g}}}_{i}}}}}$$(x) of the electrically active magnesium component are determined by the differential-conductivity method, and the total-concentration profiles Ntotal(x), by secondary-ion mass spectroscopy. It is established that the total concentration of magnesium in the samples is ~2 orders of magnitude higher than that of the electrically active component. It is also found that the diffusion coefficient $${{D}_{{{\text{M}}{{{\text{g}}}_{i}}}}}$$ of interstitial magnesium depends on the diffusion time and decreases with an increase in the duration of the process. Assumptions are made about the physical processes, which can lead to the formation of an electrically inactive component of magnesium impurity and to the dependence of the effective diffusion coefficient on time.

Electrically active centers in n-type magnesium-doped silicon crystals are studied by deep-level transient spectroscopy (DLTS). Magnesium is introduced by diffusion from a metal film on the surface at 1100°C. It is found that two levels with a similar concentration of ~6 × 1014 cm–3 dominate in the DLTS spectrum; the value approximately corresponds to the interstitial magnesium (Mgi) concentration expected from diffusion conditions and published data on the Hall effect. The dependence of the electron emission rate from these levels on the electric-field strength agrees qualitatively with the Poole–Frenkel effect, which indicates the donor nature of both levels, although the absolute value of the effect differs from theoretical value. The activation energies of these levels found by the extrapolation of emission rates measured at various temperatures to zero field are 112 and 252 meV, which coincides within the accuracy with energies of ground states of the first and second donor levels of Mg determined previously from optical absorption. Thus, it is shown that when using high-quality initial material and the selected diffusion mode, interstitial magnesium atoms are the dominant centers with levels in the upper half of the band gap.

Magnesium (Mg) atoms in interstitial positions of a silicon host lattice form double donor centers. The binding energy of the neutral $\mathrm{M}{\mathrm{g}}^{0}$ state corresponds to midinfrared wavelengths. Due to its interstitial character, the outer orbitals of Mg atoms can form specific bonds with different trace elements in the silicon crystal. These occur as single and double donors that become detectable by infrared spectroscopy when the concentration of either Mg or the dopant coupled to it is sufficiently large. Infrared absorption spectroscopy at high magnetic fields allows us to observe the Zeeman effect of several shallow Mg-related donor complexes and neutral Mg donors, very similar to those observed for hydrogenlike centers. The quadratic Zeeman effect indicates a hydrogenlike center structure of the excited states and spatial localization of complexes with a single excess electron in its outer shell, which are formed by Mg with an impurity atom. In contrast, Mg complexes formed by bonds with two electrons are closer to substitutional double donors in silicon.

Diatomic centers of double donor doped silicon have lower chemical shifts as compared to the corresponding atomic impurity and by this essentially extend spectral sensitivity of silicon extrinsic infrared detectors towards longer wavelengths. Additional expansion of the detector spectral band, up to the effective-mass approximated theoretical value of about 2.7 THz, can be obtained by photothermal infrared absorption originated from intracenter transitions of a dopant. Due to large energy gaps between lowest excited states of double donors in silicon related photothermal transitions have not been considered yet as applicable for photoconductive light detection. We have investigated the operational conditions suitable for expanding the low temperature detection wavelength cut-off of selenium doped silicon infrared detectors towards 6.2 μm.

Magnesium in silicon primarily occupies an interstitial site, where it acts as a moderately deep double donor. It has recently been shown that interstitial magnesium can pair with the substitutional acceptor boron to form a shallow single-donor center. In this work, we demonstrate analogous complexing with the other group-III acceptors Ga, In, and Al. We observe the odd-parity excited states of each shallow donor complex in absorption spectra, from which the ionization energies are obtained. These complexes can localize excitons, and we observe the donor bound exciton transitions of all four centers in photoluminescence spectra. The Mg-acceptor complexes are found to obey Haynes rule, which predicts a linear relationship between donor ionization energy and donor bound exciton localization energy.

The diffusion doping of dislocation-free single-crystal silicon with magnesium is studied in the temperature range 1000–1200°C. The conventional sandwich method is used as the doping method. It is found that the diffusion coefficient of magnesium is described by a universal Arrhenius curve in the extended temperature range 600–1200°C, with data earlier obtained for the range 600–800°C taken into consideration. The relatively low activation energy of diffusion transport (1.83 eV) is indicative of the interstitial mechanism of impurity diffusion.

The results of experiments aimed at the observation of split 1s states in Mg-doped Si are reported. From the results, it is possible to determine the chemical shift and exchange interaction energy of a neutral Mg donor in Si. The position of the 1s(E), 1s(T2), and 2s(A1) parastates determines the possibility for attaining population inversion and the specific mechanism of stimulated Raman scattering. The energy of the 1s(T2) parastate is determined from the position of the Fano resonances in the photoconductivity spectrum of Si:Mg at T = 4 K, and the energies of the 1s(T2) and 1s(E) orthostates from the transmittance spectra at elevated temperatures. On the basis of the experimental data, the relaxation rates are estimated, and the possible mechanisms of stimulated emission are analyzed.

We use the greatly improved optical linewidths provided by highly enriched $^{28}$Si to study a photoluminescence line near 1017 meV previously observed in the luminescence spectrum of natural Si diffused with Mg, and suggested to result from the recombination of an isoelectronic bound exciton localized at a Mg-pair center. In $^{28}$Si this no-phonon line is found to be comprised of five components whose relative intensities closely match the relative abundances of Mg-pairs formed by random combinations of the three stable isotopes of Mg, thus confirming the Mg-pair hypothesis. We further present the results of temperature dependence studies of this center that reveal unusual and as yet unexplained behaviour., 5 pages, 4 figures

We have performed high field magnetoabsorption spectroscopy on silicon doped with a variety of single and double donor species. The magnetic field provides access to an experimental magnetic length, and the quadratic Zeeman effect, in particular, may be used to extract the wave-function radius without reliance on previously determined effective mass parameters. We were, therefore, able to determine the limits of validity for the standard one-band anisotropic effective mass model. We also provide improved parameters and use them for an independent check on the accuracy of effective mass theory. Finally, we show that the optically accessible excited-state wave functions have the attractive property that interactions with neighbors are far more forgiving of position errors than (say) the ground state.

The deep double donor levels of substitutional chalcogen impurities in silicon have unique optical properties which may enable a spin/photonic quantum technology. The interstitial magnesium impurity (Mg$_i$) in silicon is also a deep double donor but has not yet been studied in the same detail as have the chalcogens. In this study we look at the neutral and singly ionized Mg$_i$ absorption spectra in natural silicon and isotopically enriched 28-silicon in more detail. The 1s(A$_1$) to 1s(T$_2$) transitions, which are very strong for the chalcogens and are central to the proposed spin/photonic quantum technology, could not be detected. We observe the presence of another double donor (Mg$_{i*}$) that may result from Mg$_i$ in a reduced symmetry configuration, most likely due to complexing with another impurity. The neutral species of Mg$_{i*}$ reveal unusual low lying ground state levels detected through temperature dependence studies. We also observe a shallow donor which we identify as a magnesium-boron pair.

The decomposition of a solid solution of interstitial magnesium Mgi in silicon is studied. Float-Zone dislocation-free single-crystal n-Si with a resistivity of ~8 × 103 Ω cm and oxygen and carbon contents of ~5 × 1014 cm–3 and ~1 × 1015 cm–3 is used in the experiments. The samples are doped using the diffusion sandwich method at T =1100°C followed by quenching. Decomposition of the supersaturated Mgi solid solution is studied by observing the kinetics of increasing the resistivity of doped samples resulting from their annealing in the range T= 400–620°C. It is found that the decomposition is characterized by an activation energy of Ea ≈ 1.6 eV, which is close to the previously determined diffusion activation energy of Mgi in silicon. It is also shown that Si:Mg exhibits stable properties at temperatures not exceeding 400°C, which is important for its possible practical application.

The diffusion of magnesium impurity in the temperature range T = 600–800°C in dislocation-free single-crystal silicon wafers of p-type conductivity is studied. The surface layer of the wafer doped with magnesium by the ion implantation technique serves as the diffusion source. Implantation is carried out at an ion energy of 150 keV at doses of 5 × 1014 and 2 × 1015 cm–2. The diffusion coefficient of interstitial magnesium donor centers (Di) is determined by measuring the depth of the p–n junction, which is formed in the sample due to annealing during the time t at a given T. As a result of the study, the dependence Di(T) is found for the first time. The data show that the diffusion process occurs mainly by the interstitial mechanism.

Noise in a low-current Townsend discharge in argon and nitrogen is studied. Experiments were performed in a ``semiconductor--gas-discharge'' structure constituted by a short plane-parallel discharge gap and a high-resistivity photosensitive semiconductor electrode. The noise of optical emission from gas excited by the discharge was investigated with a photomultiplier. Experiments were done at the room temperature of the discharge structure. According to the obtained data, the noise of discharge glow in Ar is astonishingly low---similar to that earlier found for the cryogenic discharge in this gas. At equal time-average photon fluxes emitted by discharges in both gases, the noise of gas glow in nitrogen substantially exceeds the corresponding value for argon. A statistical processing of signals of glow brightness for the two gases revealed the origin of this difference: While the power spectral density of noise in nitrogen is specified by a band of frequencies with the increased density, in argon it is nearly constant in an extended frequency range. At the same time, intensity of noise is practically the same for both gases in the ranges of low and high frequencies. The relationship of the increased noise in nitrogen with a low critical current density for oscillatory instability of the Townsend discharge in this gas is considered.

The paper describes a study of the electron energy distribution function in the self-sustained direct current (dc) Townsend discharge. A three-electrode microdischarge structure with a plane-parallel arrangement of electrodes is applied in the experiments. The device comprises two discharge gaps of a small width having a common electrode in the form of a fine-grained metal mesh. A high-resistivity cathode to the first gap is applied, which ensures the spatial uniformity of the Townsend discharge in the gap. The second gap serves as a retarding field analyzer of energy of electrons that are generated in the region of the Townsend discharge and pass through cells in the grid electrode. Experiments are carried out for discharges in argon and nitrogen near the minimum of the Paschen curve. According to the data obtained, shapes of the distribution function for the investigated gases are different: for Ar, a local maximum at energies of 1–3 eV is observed in the distributions, in contrast to N 2. At the same time, the effective electron temperature—determined from the high-energy tail of a distribution—is close for both gases and lies in the range of 0.8–1.9 eV. This is significantly lower than electron energies that give numerical calculations for E / N values corresponding to the conditions of experiments. Among the possible reasons for the difference is the fundamental property of a dc Townsend discharge: electrons in the subanode layer—where they are accumulated and from where they pass to the analyzer—gain energy mainly on a relatively small ionization length in the gas.

We have manufactured mid-infrared chalcogen donor centres in silicon by high-temperature diffusion doping. Electrical characterisation has shown that we can control the ratio of different donor centre concentrations. FT-IR spectroscopy reveals very narrow lines in the mid-infrared spectral band. We have now performed the first time-domain measurements on the donor centre excited states. Our preliminary results suggest excited state lifetimes with nanosecond timescales.

Subnanosecond dynamics of optically excited electrons bound to excited states of neutral magnesium donor centers in silicon has been investigated. Lifetimes of nonequilibrium electrons have been derived from the decay of the differential transmission at photon energies matching the intracenter and the impurity–to–conduction band transitions. In contrast to hydrogen-like shallow donors in silicon, significantly longer lifetimes have been observed. This indicates weaker two-phonon and off-resonant interactions dominate the relaxation processes in contrast to the single-intervalley-phonon assisted impurity-phonon interactions in the case of shallow donors in silicon.

Doping of silicon with magnesiumis investigated by a sandwich diffusion technique. Temperature dependence of the diffusion coefficient in the dislocation-free silicon in the range of 1000–1200 8C is determined. It obeys the Arrhenius behavior over the range of 600–1200°C, when the data obtained earlier for the lower temperatures are taken into consideration. Preliminary results on Mg diffusion in the dislocated crystals are also presented. The dislocation-free Si:Mg samples are investigated with the Hall-effect measurements and the low-temperature Fourier spectroscopy. A decrease in concentration of Mg interstitials (about 15%) has been observed after 31 months of the samples storage at room temperature, when a commercially available FZ silicon was used as a starting material. The effect of the samples degradation is proposed to be due to a formation of Mg-O complexes. When using a special silicon purified from oxygen and carbon with concentrations below or equal to 1.5 x 10^14 and 5 x 10^14 cm ^-3, respectively, a decrease in the density of interstitial magnesium has not been noticed during this period. The storage of Si:Mg samples prepared from pure silicon gives rise to the formation of an unknown center, whose ionization energy is between the corresponding values for the interstitial Mg^0 centers and (Mg-O)^0 complexes.

Just as phosphorus in silicon produces a hydrogenic defect, the double donor selenium in silicon is an analog of helium. We have measured the impurity absorption spectrum at high magnetic field, and we show that the odd-parity excited states of Si:Se behave identically to those of Si:P. This fact allows us to isolate the electron-electron interactions (exchange and correlation) in the ground state from the quadratic Zeeman effect. The field tuning allows us to put upper limits on the strength of some of these interactions (e.g., at 30 T the electron-electron correlation interaction in the ground state of Se is less than about 40 \ensuremath{\mu}eV; at 30 T the quadratic Zeeman energy in the ground state of P is less than about 200 \ensuremath{\mu}eV).

The influence of stationary spatially homogeneous Townsend discharge on the (1 0 0) surface of semi-insulating GaAs samples is studied. Samples exposed to both electrons and ions in a nitrogen discharge at a current density j = 60 µ Ac m −2 are studied by means of x-ray photoelectron spectroscopy, ellipsometry and atomic force microscopy. It is shown that an exposure to low-energy ions (

The temperature dependence of the properties of the low-current Townsend discharge in nitrogen is studied. The experiments are carried out on a device with a high-resistivity semiconductor electrode in the temperature range 85–292 K at a current density not exceeding 25 μA cm−2. The discharge gap of the device is 0.85 mm, while the nitrogen density corresponds to the gas pressure Pa (49.5 Torr) at T = 292 K. The earlier increase found in the discharge sustaining voltage in time at a fixed current is quantitatively investigated for the cryogenic discharge. The relaxation is accompanied by transitions to new discharge states with an increased noise intensity. The characteristic time of the relaxation is hundreds of seconds. The effect is especially pronounced in the range of 100–150 K and is relatively weak at room temperature. The interpretation of the experimental data is based on the hypothesis that considers the formation of neutral aggregates of nitrogen in the form [(N2) n ]− in the discharge volume. The condensation of the clusters on the cathode leads to a change in its emission properties, which changes the properties of the discharge.