The solubility of impurity magnesium, which was introduced by diffusion in the temperature range of 1100-1300oC in silicon, is studied by secondary-ion mass spectrometry. It is demonstrated that, with the electrically inactive impurity component taken into account, the maximum solubility of magnesium in silicon is 1-2 orders of magnitude lower (and the diffusion coefficient is higher) than the values reported earlier. Keywords: silicon, doping, magnesium impurity, solubility.

Experimental results on the observation of terahertz luminescence under optical excitation of silicon doped with neutral helium-like magnesium donors under photoionization conditions under uniaxial stress are presented. Possible options for creating stimulated radiation sources based on Si:Mg under optical excitation are considered. The possibility of obtaining inversion at the lowest odd level and significant gain coefficients is difficult due to the rather short relaxation time of the 2p0 level. The possibility of using an alternative inversion mechanism presupposes knowledge of relaxation routes. The mechanism of stimulated Raman scattering is theoretically considered and it is shown that terahertz stimulated radiation with optical excitation of double magnesium donors in silicon can be achieved using the mechanism of electronic-type Raman scattering.

Методом масс-спектроскопии вторичных ионов исследована растворимость в кремнии примеси магния, введенного путем диффузии в интервале температур 1100-1300oС. Показано, что с учетом электрически неактивной компоненты примеси максимальная растворимость магния в кремнии на 1-2 порядка меньше, а коэффициент диффузии выше, чем опубликованные ранее данные. Ключевые слова: кремний, легирование, примесь магния, растворимость.

We have combined ultrafast time-resolved techniques, available at European infrared free-electron laser facilities (HFML-FELIX and ELBE), for the analysis of intracenter relaxation processes in an atomiclike energy spectrum of the double donor magnesium in silicon. We show that complementary techniques enable the accurate analysis of complex transients inherent to strongly absorbing multilevel media. From the combined analysis of degenerate pump-probe, photon echo, and transient grating spectroscopy, we find short decay times of (10 +/- 1) ps and (30 +/- 3) ps for the 2p0 and 2p +/- states, respectively. These high decay rates exceed those obtained earlier for the shallow, one-electron donors in silicon, where intracenter relaxation profits from interaction with a single phonon of a host lattice.

Infrared absorption cross sections and corresponding oscillator strengths of several intracenter transitions of double donors in silicon, interstitial magnesium (Mg; group IIA) and substitutional chalcogens (Ch = S; Se; group VI), were determined for impurity densities in the ranges 1 x 10(14)-1.6 x 10(15) atoms/cm(3) for Mg and 2 x 10(13)-2 x 10(16) atoms/cm(3) for chalcogens. The concentrations of electrically active atomic and diatomic donor centers were derived from the Hall effect measurements. The experimental integrated cross sections were obtained from low-temperature impurity absorption spectra. The oscillator strengths of related donor transitions were derived and compared with those for shallow single donors in silicon, both determined experimentally and predicted theoretically. The transitions of oscillator strengths of double donors follow the decreasing trend with decreasing radius of donor ground states and increasing an impurity binding energy.

The optical properties of magnesium impurity in silicon, whose atoms at interstitial positions in the lattice are deep double donors with an ionization energy of 107.56 meV in the neutral state, were studied. For optical transitions from the ground state of a neutral center to the excited levels 2p0 and 2p, the absorption cross sections and oscillator strengths were determined. These parameters were calculated from the impurity absorption spectra that were measured at T  K in samples with different magnesium concentrations. The deep donor content in the samples was determined using Hall effect measurements in the temperature range 78–300 K. The obtained characteristics of intracenter transitions in magnesium were compared with the corresponding literature data for shallow Group V donors in silicon, which are substitutional impurities. It was found that the optical characteristics of the investigated transitions in magnesium are consistent with the dependences of the corresponding parameters on the ionization energy for shallow donors, extrapolated to the region of larger electron binding energies.

Magnesium (Mg) atoms, diffused in silicon (Si) lattice at high temperatures, tend to form specific bonds to host Si atoms, to other Mg atoms as well as to other defects in a Si crystal. These electrically active donors exist either as isolated atomic type centers or as complexes coupling magnesium to other trace elements in silicon. We report on shallow Mg-related donor centers in moderately doped Si:Mg crystals which are distinguished by their infrared absorption spectra. These complexes have energy spectra, relatively dense filling two separated infrared ranges, 30-95 meV and 105-130 meV, having clearly different genesis. These centers are observed in silicon of various purification degree, including high-purity crystals with low oxygen and carbon content. We assign the formation of such localized states in Si:Mg to electrically active donor complexes with different numbers of magnesium atoms, similar to those formed by interstitial oxygen in silicon. The results obtained are incorporated into the general phenomenon of formation of shallow donors in silicon which is related to interaction of impurities in the semiconductor. Subject areas: Semiconductor Physics, Diffusion Doping, Silicon.

Magnesium (Mg) atoms in interstitial positions of a silicon host lattice form double donor centers. The binding energy of the neutral Mg-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.

Profiles of both electrically active and total concentration of magnesium impurity in silicon were measured. Diffusion was performed into the floating zone dislocation-free n-type silicon at the temperatures Tdiff = 1000, 1100◦C and duration from 0.5 to 22.5 h. The depth profiles of the electrically active interstitial magnesium concentration NMgi (x) were determined by differential conductivity method, while the total concentration profile Ntotal(x) — with secondary ion mass spectroscopy. The total concentration of magnesium was found to be almost two orders higher than the concentration NMgi . It turned out that the effective diffusion coefficient DMgi decreases with the diffusion time. Possible physical processes responsible for formation of the electrically inactive component of magnesium impurity and the dependence of effective diffusion coefficient on time are discussed.

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.

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.

AbstractThe decomposition of a solid solution of interstitial magnesium Mg_ i in silicon is studied. Float-Zone dislocation-free single-crystal n -Si with a resistivity of ~8 × 10^3 Ω cm and oxygen and carbon contents of ~5 × 10^14 cm^–3 and ~1 × 10^15 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 Mg_ i 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 E _ a ≈ 1.6 eV, which is close to the previously determined diffusion activation energy of Mg_ i 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.

An anodic oxidation of GaAs substrates in a non-self-sustained low-current dc Townsend discharge is investigated. The process is carried out at the room temperature in a three-electrode microreactor filled by 98%Ar + 2%O-2 gas mixture. Investigation of the oxidation kinetics indicates that the formed oxide is characterized by a high resistivity, rho similar to 10(11) Omega center dot cm. It is demonstrated the application of the method for formation of oxide films with dimensions of tens of microns, which thickness is on the nanometer scale. Examination of the "GaAs substrate - oxide layer" interface using the high resolution transmission electron microscopy has revealed that the oxide is characterized by the amorphous structure.

AbstractElectrically 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 × 10^14 cm^–3 dominate in the DLTS spectrum; the value approximately corresponds to the interstitial magnesium (Mg_ i ) 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.

The decomposition of a solid solution of interstitial magnesium Mg i in silicon is studied. Float-Zone dislocation-free single-crystal n -Si with a resistivity of ~8 × 10 3 Ω cm and oxygen and carbon contents of ~5 × 10 14 cm –3 and ~1 × 10 15 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 Mg i 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 E a ≈ 1.6 eV, which is close to the previously determined diffusion activation energy of Mg i 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 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(T-2), and 2s(A(1)) parastates determines the possibility for attaining population inversion and the specific mechanism of stimulated Raman scattering. The energy of the 1s(T-2) 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(T-2) 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.

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 N2. 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.

AbstractThe results of experiments aimed at the observation of split 1 s 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 1 s ( E ), 1 s ( T _2), and 2 s ( A _1) parastates determines the possibility for attaining population inversion and the specific mechanism of stimulated Raman scattering. The energy of the 1 s ( T _2) 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 1 s ( T _2) and 1 s ( 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.

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 × 10 14 cm –3 dominate in the DLTS spectrum; the value approximately corresponds to the interstitial magnesium (Mg i ) 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.

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.