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 ( mK). We present also data for the magnetoresistivity and the thermal conductivity of the same sample, and the calculated specific heat . We compare with earlier direct measurements, and we try to explain the behaviour of D, , and 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.