Oxygen Concentration In Crystals Research Articles

Simulating the horizontal growth process of silicon ribbon

In this paper, we present a solidification growth model that primarily describes the principal components of horizontal ribbon growth process, but also discusses the interaction between fluid flow and heat transfer, crystallization dynamics, and the effects of oxygen impurity distribution in melts, particularly with respect to the morphology of the interface. The effects of the jet cooling rate, pulling speed, and transfer coefficient on solute transport were studied. The results showed that a higher jet velocity produces a sharper temperature gradient at the interface and a stronger Marangoni effect, facilitates solute transport in the silicon melt, and promotes higher oxygen concentration in crystal. The stronger Marangoni convection causes more rapid oxygen transfer in the silicon melt and a higher oxygen concentration. Solidification front increases the downward flow velocity of the eddy current as the pulling speed is increased; this leads to a decrease in solute concentration at the interface. An increase in the downward flow of the vortex confluence facilitates the reduction of solute concentration in the crystal. An increase in the upward flow of the vortex confluence will increase the concentration in the crystal. The oxygen concentration is concentrated at the top and bottom of the silicon ribbon.

Oxygen Impurity in Germanium Single Crystals Determination by Infrared Spectrometry

Oxygen impurity in Germanium single crystals has been characterized using Fourier transformed infrared spectrometry. The crystals were grown by Czochralski method in an argon atmosphere. The oxygen concentration in crystals was determined on optical density from the absorption band at 843 cm−1. It was established that oxygen dissolved concentration in Germanium is variable from 0,2·1016 to 1,3·1016 сm−3. The oxygen band maximum shifts toward 856 cm−1 when its concentration increases under the influence of annealing in the oxygen containing atmosphere with ≤ 10−3 Па.

Oxygen doped Ge crystals Czochralski-grown from the B 2O 3-fully-covered melt

Local vibrations of oxygen in Ge crystals grown from a melt fully covered by B 2O 3 were evaluated by Fourier-transform infrared spectroscopy. Ge single crystals containing oxygen were grown by the Czochralski method under various growth conditions. Oxygen concentrations in the crystals were determined to be in the range between 8.5 × 10 15 and 5.5 × 10 17 cm −3 from the infrared absorption at 855 cm −1 originating in local vibration of Ge–O i –Ge quasi-molecules. Absorption peaks relating to GeO x , SiO x and Si–O i –Si were not detected in the as-grown crystals. The calibration coefficient for determining oxygen concentration in Ge crystals from the absorption peak intensity at 1264 cm −1 was estimated to be 1.15 × 10 19 cm −2.

Czochralski-growth of germanium crystals containing high concentrations of oxygen impurities

Oxygen-containing germanium (Ge) single crystals with low density of grown-in dislocations were grown by the Czochralski (CZ) technique from a Ge melt, both with and without a covering by boron oxide (B 2O 3) liquid. Interstitially dissolved oxygen concentrations in the crystals were determined by the absorption peak at 855 cm −1 in the infrared absorption spectra at room temperature. It was found that oxygen concentration in a Ge crystal grown from melt partially or fully covered with B 2O 3 liquid was about 10 16 cm −3 and was almost the same as that in a Ge crystal grown without B 2O 3. Oxygen concentration in a Ge crystal was enhanced to be greater than 10 17 cm −3 by growing a crystal from a melt fully covered with B 2O 3; with the addition of germanium oxide powder, the maximum oxygen concentration achieved was 5.5×10 17 cm −3. The effective segregation coefficients of oxygen in the present Ge crystal growth were roughly estimated to be between 1.0 and 1.4.

Effect of crucible rotation on oxygen concentration during unidirectional solidification process of multicrystalline silicon for solar cells

We studied the effects of crucible rotation on distribution of oxygen concentration in a crystal during the unidirectionally solidification process of multicrystalline silicon for solar cells. Oxygen concentration in the melt increased when crucible rotation rate was increased. Oxygen concentration in the silicon crystal was distributed inhomogeneously in the radial direction when crucible rotation rate was increased. This is due to suppression of oxygen transport. Consequently, less oxygen was transported from the crucible wall to the center of the melt. We found that oxygen concentration is small in the whole ingot and homogenized in the radial direction when crucible rotation rate during the solidification process is set to 1 rpm.

Oxygen transport mechanism in Si melt during single crystal growth in the Czochralski system

Silicon single crystals were grown in crucibles with and without a carbon sheet at the bottom to investigate how oxygen dissociates from the crucible and transfers to the crystals. Oxygen concentration in the crystals grown in the sheet-attached crucible was lower than that of crystals grown in the sheetless crucible when crucible rotation rate was high. A three-dimensional numerical simulation clarified that with a high crucible rotation rate, about 20% of the oxygen in the grown crystals was transferred by convection in the melt from the bottom of the crucible. For a low crucible rotation rate, a melt with a small oxygen concentration was directly transferred from the gas-melt interface to the crystal-melt interface; therefore, oxygen concentration in crystals grown at a low crucible rotation rate was lower than that for crystals grown at a high rotation rate.

Dynamic Oxygen Equilibrium in Silicon Melts during Crystal Growth by the Czochralski Technique

A model for the dynamic oxygen concentration in silicon melts during Czochralski growth is presented. The model is found to be in good agreement with experimental results and to account for first order effects on both the absolute oxygen concentration and its axial variations in grown crystals. Approaches aimed at achieving controllable and axially uniform oxygen concentration in crystals grown by the method are discussed.