Polycrystalline growth

Some crystals appear to become prone to attrition once they have been grown beyond a certain critical size in an agitated crystallizer. To some extent this can be attributed to increased damage from the agitator as higher rotational speeds are needed to keep them in suspension. Sometimes the critical size coincides with the onset of polycrystalline growth which tends to make the crystals friable. Polycrystalline growth, however, may not only render the crystals mechanically weak, but may even make the crystals thermodynamically... 

The stmcture of the polysihcon depends on the dopants, impurities, deposition temperature, and post-deposition heat annealing. Deposition at less than 575°C produces an amorphous stmcture deposition higher than 625°C results in a polycrystalline, columnar stmcture. Heating after deposition induces crystallization and grain growth. Deposition between 600 and 650°C yields a columnar stmcture having reasonable grain size and (llO)-preferred orientation. 

Purified polycrystalline CVD siUcon from this reaction is then melted and a single-crystal boule weighing as much or more than 50 kg, and having a diameter up to 20 cm, is pulled from the melt by C2ochralski growth (8). Metallurgical-grade siUcon is not sufficientiy pure for appHcations in electronics... 

The process of sintering by vapour phase transport is probably important to the growth of single crystals of solids from polycrystalline samples in a closed system, where the vapour species are the transporting gas, which may have the same or different chemical composition from die solid. An example where... 

The obvious application of microfocus Raman spectroscopy is the measurement of individual grains, inclusions, and grain boundary regions in polycrystalline materials. No special surface preparation is needed. Data can be obtained from fresh fracture surfeces, cut and polished surfaces, or natural surfeces. It is also possible to investigate growth zones and phase separated regions if these occur at a scale larger than the 1-2 pm optical focus limitation. 

---