The local order around Mn atoms in the Mn-implanted Si samples, with ferromagnetic properties, has been investigated by use of x-ray-absorption spectroscopy techniques. Analysis of both extended x-ray-absorption fine structure and x-ray absorption near-edge structure spectra clearly indicates that Mn ions are located neither in the substitutional nor in the interstitial position in the Si lattice, but depending on how the samples were prepared, they have five to eight near neighbors.

Photoluminescence (PL) of porous silicon (pSi) prepared from Czochralski silicon (Cz-Si) annealed up to 1620 K at enhanced pressure of argon up to 1 GPa (HP-HT treatment) was investigated. The intensity of PL with maximum at 680±720 nm decreases with the pressure for pSi prepared from the substrates treated at 1400 K, and increases with the pressure for pSi prepared from the substrates treated at 1620 K. The pSi films prepared from the HP-HT treated substrates were relaxed, contrary to those on the substrates annealed at 1620 K for 30 min at 10 5 Pa. Although our results revealed that photoluminescence properties of pSi depend significantly on the presence of defects created during the oxygen precipitation process, the role of other defects such as non-radiative recombination centres and metallic contamination should be still under consideration.

We have used local vibrational mode (LVM) spectroscopy to monitor the formation of oxygen-related thermal double donors (TDDs) at 450 • C and their annihilation at 650 • C in carbon-lean Czochralski-grown (Cz-) Si crystals. A few samples were treated at 650 • C under high hydrostatic pressure. It is found that the annihilation of TDDs at 650 • C results not only in a partial recovery of the interstitial oxygen, but also in the appearance of a number of new O-related LVM bands in the range 990-1110 cm −1 . The positions of these lines and their shapes are identical to those observed for Cz-Si irradiated with electrons or neutrons and annealed at 600-700 • C. Since the lines appear upon annealing out of VO 3 and VO 4 defects in irradiated samples, they are suggested to arise from VO m (m > 4) complexes. In both kinds of samples, pre-annealed and preirradiated, the new LVM bands disappear upon prolonged annealing at 650 • C while enhanced oxygen precipitation occurs. The VO m defects are suggested to serve as nuclei for oxygen precipitates developing at around 650 • C. High hydrostatic pressure is found to enhance further (up to 4-5 times) the oxygen precipitation process at 650 • C in the samples pre-annealed at 450 • C.

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The formation kinetics of Thermal Double Donors, a dominant family of thermal donors in Czochralskigrown silicon annealed at T < 600 °C, is studied in detail. A striking enhancement effect of hydrostatic pressures of about 1 GPa on their formation processes, even in a temperature region of thermal instability of these donor centers at about T = 600 °C under normal conditions, is clearly demonstrated. The experimental data obtained in the present work are in agreement with the recent theoretical calculations of oxygen diffusion and agglomeration processes in heat-treated Si.It is well known that oxygen impurity atoms in Czochralski-grown silicon (Cz-Si) being available in concentrations much higher than the oxygen solubility at room temperature are prone to agglomeration upon heating. Heat treatment of Cz-Si at T < 500 °C gives rise to the formation of a family of Thermal Double Donors (TDDs) consisting of more than 16 centres with shallow and deep energy states in the regions between 44 meV and 70 meV and between 100 meV and 150 meV, respectively [1, 2]. The electrical properties of Cz-Si heat treated at T < 500 °C are mainly determined by this family of thermal donors. The characteristic features of oxygen diffusion and agglomeration processes in annealed Cz-Si have recently been reviewed in [3]. Despite a vast amount of information available in the literature the key steps in these processes are still a matter of discussion. Among many well-known factors producing considerable effects on the TDD formation processes, e.g. heat-treatment regimes, the presence of isovalent impurities C and Ge, and so on, the effects of compressive stresses of about 1 GPa leading to enhanced formation of thermal donors in annealed Cz-Si [4,5] are relatively little studied. The purpose of the present work is to study the formation kinetics of TDDs in a more systematic way. This provides a solid basis for computational simulations giving a clue for the complex nature of oxygen aggregates in Si.