Thermal-conductivity measurements of GaAs/AlAs superlattices using a picosecond optical pump-and-probe technique

We present measurements of the lattice thermal conductivity ${\kappa }_{\perp }$ normal to the interfaces of $(\mathrm{GaAs}{)}_n/(\mathrm{AlAs}{)}_n$ superlattices with n between 1 and 40 monolayers. The conductivity was measured by an optical pump-and-probe technique in the temperature range of 100 to 375 K. In the experiment, an Al film is deposited onto a superlattice sample, and the rate at which this film cools by conduction into the superlattice is determined. We find a general decrease in ${\kappa }_{\perp }$ with a reduction of the superlattice period. At 300 K, ${\kappa }_{\perp }$ of the $(\mathrm{GaAs}{)}_{40}/(\mathrm{AlAs}{)}_{40}$ superlattice is approximately three times less than $\kappa$ of bulk GaAs, and ${\kappa }_{\perp }$ of the $(\mathrm{GaAs}{)}_1/(\mathrm{AlAs}{)}_1$ superlattice is an order of magnitude less than $\kappa$ of bulk GaAs. We discuss the decrease in ${\kappa }_{\perp }$ compared to the bulk constituents in terms of extrinsic and intrinsic scattering mechanisms.