| We present investigations of the thermal conductivity of novel semiconductor and insulator thin films. Measurements of the thermal conductivity are carried out by means of an ultrafast optical pump and probe technique. In this technique, the sample is heated by an ultrashort (<200 fs) pump pulse of laser light and is probed by a time delayed probe pulse derived from the same laser source. The heating due to the pump pulse produces a small change in reflectivity Δ R(t), of the sample, which can be monitored as a function of time by the probe pulse. The rate at which ΔR( t) decays with time yields information about the thermal conductivity κ, of the sample. We report measurements of κ of novel “low- k dielectric” materials that are currently of interest to the microprocessor industry. We also report measurements of κ of nitride thin films that have potential applications in high power field effect transistors and solid-state lasers.; In addition to these experimental investigations, we report on molecular dynamics simulations of heat flow in semiconductor superlattices. Superlattices are known to exhibit reduced thermal conductivity when compared with their bulk constituent materials, but theoretical predictions found in the literature underestimate the magnitude of the experimentally observed reduction. We use a simple, classical model of an FCC lattice in order to simulate these structures. A variety of superlattices is studied, and the results of our simulations provide an explanation for the disagreement between current theory and experimental results. |
