Thermodynamics and kinetics of silicon under conditions of strong electronic excitation

We present a detailed analysis of a recently-developed empirical potential to describe silicon under conditions of strong electronic excitation. The parameters of the potential are given as smooth functions of the electronic temperature T-e, with the dependence determined by fitting to finite-temperature density-functional theory calculations. We analyze the thermodynamics of this potential as a function of the electronic temperature T-e and lattice temperature T-ion. The potential predicts phonon spectra in good agreement with finite-temperature density-functional theory, including the previously predicted lattice instability. We predict that the melting temperature T-m decreases strongly as a function of T-e. Electronic excitation has a strong effect on the rate of crystallization from the melt. In particular, high T-e results in very slow kinetics for growing crystal from the melt, due mainly to the fact that diamond becomes much less stable as T-e increases. Finally, we explore annealing amorphous Si (a-Si) below T-m, and find that we cannot observe annealing of a-Si directly at high T-e. We hypothesize that this is also due to the decreased stability of the diamond structure at high T-e. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3554410]