Investigation of Si Dendrites by Electron-Beam-Induced Current

This paper reports on electron-beam-induced current (EBIC) characterization of special multicrystalline Si ingot by dendritic growth under high undercooling. Grain boundaries (GBs), dislocations, and their interaction with carbon related precipitates were investigated. The difference between grains from dendrite and non-dendrite growth was compared. In dendrite grains, parallel twins were frequently found. In non-dendrite grains, irregular GBs of various characters co-existed. Both parallel twins and irregular GBs exhibited dark EBIC contrast at room temperature, indicating the presence of minority carrier recombination centers due to impurity contamination. However, sometimes in non-dendrite grains GBs were visualized with bright EBIC contrast with enhanced collection of charge carriers. The origin of the abnormal bright EBIC contrast was explored and it turned out to be SiC related precipitates, which made GBs conduction channels for electron transport.

Study of the Localized Heating of Si Solar Cells by Thermal Imaging and Scanning Electron Microscopy

The aim of this study was to investigate the localized solar cells heating by thermal imaging, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The electrical measurements and thermal infrared measurements were done on the commercial crystalline Si cells (10 cm x 10 cm). SEM was used for the observation of the localized heating. The I-V characteristics of all cells were quite similar with a small spread in the electrical parameters, while the IR images were different: some cells had quite uniform temperature profiles distribution and other ones showed the localized heating. The energy dispersive spectroscopy (EDS) analysis showed that some hot spots have high metal impurity contamination. The micro-structure investigation of hot spots revealed the micro-cracks presence. Our study found direct correlation between areas of high impurity contamination, micro cracks and hot-spot heating.

Zinc Chloride Content Analysis Methods and Special Reagent in Acidic Galvanized Solution

In recent years, because the quality of chemical materials in markets exists large difference, we found concentrations of ZnCl2 unusually high, Cl- concentration not lower and a serious shortage of KCl concentration as using traditional methods to analyze the bath. This phenomenon occured frequent. The companies that had problems were recommended to take measures to dilute ZnCl2 concentration range in 60 ~ 80g/l and add KCl and H3BO3 to the normal scope according to analysis results. However, the old problems still remained when the adjusted solution was analyzed again. The concentration of each main salt cannot be exactly determined by traditional methods because of the serious impurity contamination in the acidic galvanized solution. The concentration of ZnCl2, KCl, H3BO3 in the bath were respectively tested by new analysis methods. A comparision of the results by new methods with those by traditional methods shows that the new analysis methods are simple, fast, and have low consumption, high accuracy and good effects in practical production.

Impurity Contamination and Diffusion during Annealing in Implanted ZnO

The effect of ion implantation leading to contamination and diffusion of lithium impurity in ZnO ceramics substrates was investigated. The diffusion coefficients of Li in the implanted ZnO annealed at 1000 and 850°C were in good agreement with those in the non-implanted ZnO. At 700°C, Li diffusion in the implanted ZnO was strongly enhanced. Our results show that the defects introduced by the implantation enhance the impurity diffusion at low temperature annealing.

SIMS Study of C, O and N Impurity Contamination for Multi-Crystalline Si Solar Cells

This paper is a case study of using SIMS to quantitatively measure C, O and N impurity contamination at two sequential commercial process steps: (1) Si feedstock: 7N (modified Siemens) and 5N feedstock (UMG-Si); and (2) multi-crystalline (mc-Si) solar wafers: cut and etched, from directional solidification bricks grown from 7N and 7N/5N (80:20) feedstock. The conclusion of this study is twofold: (a) the primary opportunity to reduce C, O and N contamination in mc-Si solar cells is at the directional solidification process, and (b) the costly specification of highly pure Si feedstock is unnecessary from a C, O and N perspective if a directional solidification process is used.

Unidirectional Solidification and Single Crystal Growth of Al-rich Ti-Al Alloys

To investigate the basic mechanical and thermomechanical properties of TiAl alloys with high Aluminium content sufficiently large single crystalline domains are required. To fabricate these samples undirectional solidification in Bridgman Stockbarger furnaces and optical floating zone devices were used. Focus of investigation were grain selection and impurity contamination. Both processes allow for growth of single crystal domains of some millimetres diameter and a few centimetres length. However in a Bridgman Stockbarger furnace the long contact times with the crucible proved detrimental to oxidation issues whereas in the optical floating zone device oxidation is negligible due to containerless processing.