Molecular Dynamics Simulations On The Crystal Growth Of Silicon

Crystalline silicon solar cells are the mainstreams of photovoltaic industries. Theraw materials, all kinds of silicon crystal, come from silicon melt by crystal growth.With the market requirements of increasing crystal quality and decreasing productioncost, it is necessary to carry out some basic study during crystal growth of silicon, andthen to guide industrial production more accurately. This paper, the moleculardynamics method was applied to study the crystal growth of silicon. At first, thedifferences about melting and growth characteristics of five classical potentials forsilicon were investigated. And then the Tersoff potential was selected to calculate theatomic interactions in Si systems. Secondly, the effects of the temperatures and thecharacteristic growth planes on the crystal growth of silicon were investigated. Theresults are as follows.(1) The five potentials, including SW, MEAM, HOEP, Tersoff and EDIP, werestudied. Due to the abnormal expanded phenomenon during melting process, theEDIP potential is not suit for describing the crystal growth process of silicon; theother four potentials could show some basic laws, for example, melting at hightemperature, absorbing heat and volume shrinking during melting. After comparingthe simulative data with the corresponding experimental data of the thermal meltingpoint, thermal expansion coefficient, latent heat of fusion and surface melting rate at3300K, we found that Tersoff potential is the most suitable to describe the meltingprocess of silicon crystal, MEAM potential secondly, SW potential worse than Tersoffpotential and MEAM potential. And because of contrary to the physical laws ofthermal expansion during the heat process of the solid silicon, HOEP potential is notsuitable to describe the crystal growth process of silicon.(2) The simulation study on crystal growth of silicon at different temperatureshave found that the crystal did not grow up normally when the system temperature at1400K-1700K, grew up at temperature1800K-2400K. The growth rates of siliconincrease first, and then decrease with the temperature increasing, reaches the maximum at2200K. And it melts at2500K because the temperature is above themelting point2480K. In addition, the relationships between temperatures and thecrystal growth rates have been calculated theoretically, the results are keeping wellwith the simulative values.(3) The studies on crystal growth of silicon at different growth planes have foundthat at the same temperature, the different growth planes have different crystal growthrates. The rate in every growth planes reaches the maximum value at differenttemperature. And this result is consistent with theoretical calculation. The simulationstudies on the relationships between undercooling and the crystal growth rates indifferent growth planes of silicon show that effects of undercooling on the crystalgrowth rates varies with growth planes. And the order of the rates at the sameunderercooling is (100)>(112)>(110)>(111).