2008, Vol.18, No.6

Journal of the Korean Crystal Growth and Crystal Technology 2023 KCI Impact Factor : 0.19

pISSN : 1225-1429 / eISSN : 2234-5078
https://journal.kci.go.kr/jkcgct

For an aspect ratio (transport length-to-width) of 5, Pr = 1.13, Le = 1.91, Pe = 4.3, Cv = 1.01, PB = 20 Torr, the effects of addition of inert gas Ne on thermally buoyancy-driven convection (Gr = 2.44 × 10³) are numerically investigated for further understanding and insight into essence of transport phenomena in two dimensional horizontal enclosures. For 10 K ≤ ΔT ≤ 50 K, the crystal growth rate increases from 10 K up to 20 K, and then is slowly decreased until ΔT = 50K, which is likely to be due to the effects of thermo-physical properties stronger than the temperature gradient corresponding to driving force for thermal convection. The dimensional maximum velocity gratitude reflecting the intensity of thermal convection is directly and linearly proportional to the temperature difference between the source and crystal regions. The rate is first order-exponentially decreased for 2 ≤ Ar ≤ 5. This is related to the finding that the effects of side walls tend to stabilize convection in the growth reactor. In addition, the rate is first order exponentially decayed for 10 ≤ PB ≤ 200 Torr.

Recently the shortage of silicon resources especially for poly-silicon of purity higher than 99.9999 % leads to search for the more cheap and quick synthesizing routes for silicon feedstock. In order to solve this situation, we investigated the purification process of metallurgical grade (MG) silicon of purity around 99 % by the acid leaching and following the unidirectional solidification. MG-Si lumps are pulverized with a planetary mill, and then leached with HCl/ HNO₃/HF acid solution. As a result, the concentration of metal impurities including Al, Fe, Ca, Mn, etc. decreased dramatically. This process led to silicon content higher than 99.99 %. The purified silicon powders were compacted and have been melted and uni-directionally solidified with heat exchange method (HEM) furnace. The properties of multicrystalline silicon ingots were specific resistance of 0.3 Ω·cm and minority carrier life time (MCLT) of 3.8 μ·sec.

Hot-press sintering of AlN ceramics were carried out with Y₂O₃as sintering additive at a sintering temperature 1,750~1,850℃. The effect of Y₂O₃addition and sintering time on sintering behavior and thermal conductivity of AlN ceramics was investigated. Y₂O₃added AlN showed noticeably higher densification rate than pure AlN. The thermal conductivity of AlN specimens was promoted by the addition of Y₂O₃in spite of the formation of YAG secondary phase in AlN grain boundaries and grain boundary triple junction because Y₂O₃addition could reduced the oxygen contents in AlN lattice which is primary factor of thermal conductivity. Typically, the thermal conductivity of 5 wt% Y₂O₃added specimen was dramatically improved by the increase of sintering time because the elimination of YAG secondary phases from the grain boundary due to the evaporation, as well as the grain-growth of AlN grains.