Molecular Dynamics Study On The Anisotropic Of Growth Of Silicon Crystal

Casting multicrystalline silicon(mc-Si) solar cell has been developed rapidly and its market share grows steadily due to its low production cost and high photoelectric transformation efficiency. The improvement of the crystal quality has attracted abroad attentions because it can rise transformation efficiency. Crystal preferred orientation affects the formation of crystal defects, thus affects the crystal quality. And it exists in the three methods of casting mc-Si: common directional solidification mc-Si, mono-like mc-Si and high efficiency mc-Si. However, the orientation problem is too difficult to be investigated with experiment method. In this paper, molecular dynamics simulations has been carried out. The anisotropic growth of silicon single crystal at different undercooling or temperature, and preferred growth of double-crystal at different temperature or strain have been investigated. The interatomic force is calculated with the Tersoff potential the results showed that:(1) The sequence of monocrystalline silicon growth velocities along different planes is(100)(110)(112)(111)V >V >V >V, and the sequence of their kinetic coefficients is(100)(110)(112)(111)? >? >? >?, they have the same order. The results of layer density and diffusion coefficient showed that the arrangement and movement of the melting atoms near the solid-liquid interfaces are affected by the crystal orientations, the diffusion coefficients for melting atoms near solid-liquid interfaces is ordered as(100)(110)(112)(111)D >D >D >D, it is agreed well with the diffusion limited growth model. And hence we considered that the diffusion coefficients near the solid-liquid is one of the key factor affecting the anisotropic growth of silicon. Besides, the growth of single crystal silicon along(111) plane is lower than other planes, the reason is that the stacking fault will generate during its growth process, which may reduce its growth velocity.(2) The growth of Si bicrystal at the reduced temperature of 0.80, 0.84, or 0.88 is a competitive growth process, one grain will swallow the other grain. This prferred growth process is dominated by the kinetics factor, the grain which has the fast growth velocity will be the preferred orientation. When the reduced temperature is higher than 0.88, the crystal growth is sufficiently slow. The bicrystal that formed by two single crystals which have the similar crystal growth velocities is easier to produce dislocations. The bicrystals including(112) growth plane or(111) growth plane will generate lots of stacking fault, because these grainl will become faceted crystal growth, and the stacking fault is easier to form.(3) The strain will affect the growth of each grain in bicrystal, and then affect the speed of the preferred growth process. These bicrystals including two growth planes with similar growth velocities might change the preferred orientation under the different strain, for example, during the growth process of the(111)-(112) bicrystal, the preferred plane will change from(112) growth plane to(111) growth plane under compression strain. These bicrystals with(112) growth plane or(111) growth plane will also generate stacking fault, and the total amount of stacking fault will change while the strain changes.(100)-(111) bicrystal and(100)-(112) bicrystal will generate some dislocations penetrate the whole grain...