Specific heat of neutron-compensated heavily doped Si:P near the metal-insulator transition

The specific heat of neutron-irradiated heavily doped Si:P (3.3 . 1018 cm-3 ≤ ND ≤ 7.3 . 1018 cm-3) was measured between 0.07 and 3K and in magnetic fields between 0 and 6T. The compensation ratio was varied systematically by isochronal annealing. Characterization was done by temperature dependent measurements of Hall coefficient and electrical resistivity. The specific heat displays a minimum of the linear coefficient γ at the carrier concentration where the P impurity band is starting to be occupied. The concentration dependence of localized moments inferred from Schottky anomalies can be interpreted in terms of localized magnetic moments arising from the defect structure introduced by the irradiation and from P-derived electrons. As in uncompensated Si:P, local moments survive on the metallic side of the transition. (orig.)