Thermodynamics and kinetics of silicon under conditions of strong electronic excitation

Abstract

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 Te, 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 Te and lattice temperature Tion. 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 Tm decreases strongly as a function of Te. Electronic excitation has a strong effect on the rate of crystallization from the melt. In particular, high Te results in very slow kinetics for growing crystal from the melt, due mainly to the fact that diamond becomes much less stable as Te increases. Finally, we explore annealing amorphous Si (a-Si) below Tm, and find that we cannot observe annealing of a-Si directly at high Te. We hypothesize that this is also due to the decreased stability of the diamond structure at high Te.