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

We present measurements of the lattice thermal conductivity ${\ensuremath{\kappa}}_{\ensuremath{\perp}}$ 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 ${\ensuremath{\kappa}}_{\ensuremath{\perp}}$ with a reduction of the superlattice period. At 300 K, ${\ensuremath{\kappa}}_{\ensuremath{\perp}}$ of the $(\mathrm{GaAs}{)}_{40}/(\mathrm{AlAs}{)}_{40}$ superlattice is approximately three times less than $\ensuremath{\kappa}$ of bulk GaAs, and ${\ensuremath{\kappa}}_{\ensuremath{\perp}}$ of the $(\mathrm{GaAs}{)}_{1}/(\mathrm{AlAs}{)}_{1}$ superlattice is an order of magnitude less than $\ensuremath{\kappa}$ of bulk GaAs. We discuss the decrease in ${\ensuremath{\kappa}}_{\ensuremath{\perp}}$ compared to the bulk constituents in terms of extrinsic and intrinsic scattering mechanisms.