THERMAL-DIFFUSIVITY AND CONDUCTIVITY MEASUREMENTS FOR SI-P NEAR THE METAL-INSULATOR-TRANSITION

Silicon doped with phosphorus undergoes a metal-insulator transition ( MIT) at a critical phosphorus concentration. We present here data for the thermal diffusivity D of an insulating sample of Si:P very near th e MIT. We describe briefly our method for measuring the dependence on the magnetic field (H) of D at very low temperatures (T less than or e qual to 100 mK). We present also data for the magnetoresistivity rho(H ) and the thermal conductivity kappa of the same sample, and the calcu lated specific heat C-p = kappa/D. We compare C-p With earlier direct measurements, and we try to explain the behaviour of D, C-p, kappa and rho taking into account the complex situation in Si:P. We show that t he measurement of D at very low temperatures and under a magnetic fiel d can be a fruitful way of extracting information about the physics of doped semiconductors.