**6. Thermal conductivity predictions for GaAs/AlAs superlattices, impact of rough interfaces**

The GaAs/AlAs superlattices are important materials mainly for their optical properties. Simulations of the thermal conductivity of superlattices as a function of their period exhibit a minimum for period around 8 to 10 monolayers (Daly et al 2002, Imamura et al 2003, Chen 2005b), but this minimum is not observed in experimental measurements (Capinski et al 1999). The quality of the interfaces might be the reason to explain this discrepancy. For perfectly smooth interfaces the minimum exists, while for rough interfaces with a height as small as one monolayer the minimum disappears and the thermal conductivity increases with the periodicity of the superlattice. The works of Daly et al 2002 and Imamura and al 2003 are based on rough interfaces of one atomic layer and with a stochastic distribution of the two types of atoms that compose the superlattice.

Fig. 7. In-plane and cross-plane thermal conductivities for several shapes of the interfaces obtained by EMD and NEMD for superlattices with period 20a0 and with constant height of interfaces 6a0.

the smooth interfaces which displays the maximum anisotropy, with the in-plane thermal conductivity being more than twice larger than the cross-plane thermal conductivity; A second group contains totally random interfaces for which the two thermal conductivities exhibit their minimum values and a third group with periodic rough interfaces of a specific shape (triangular, square or cosine) where the thermal anisotropy is negligible compared to

**6. Thermal conductivity predictions for GaAs/AlAs superlattices, impact** 

The GaAs/AlAs superlattices are important materials mainly for their optical properties. Simulations of the thermal conductivity of superlattices as a function of their period exhibit a minimum for period around 8 to 10 monolayers (Daly et al 2002, Imamura et al 2003, Chen 2005b), but this minimum is not observed in experimental measurements (Capinski et al 1999). The quality of the interfaces might be the reason to explain this discrepancy. For perfectly smooth interfaces the minimum exists, while for rough interfaces with a height as small as one monolayer the minimum disappears and the thermal conductivity increases with the periodicity of the superlattice. The works of Daly et al 2002 and Imamura and al 2003 are based on rough interfaces of one atomic layer and with a stochastic distribution of

Fig. 7. In-plane and cross-plane thermal conductivities for several shapes of the interfaces obtained by EMD and NEMD for superlattices with period 20a0 and with constant height of

the uncertainties of the methods.

the two types of atoms that compose the superlattice.

**of rough interfaces** 

interfaces 6a0.
