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 the 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 equal to 100 mK). We present also data for the magnetoresistivity rho(H) and the thermal conductivity kappa of the same sample, and the calculated 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 the measurement of D at very low temperatures and under a magnetic field can be a fruitful way of extracting information about the physics of doped semiconductors.