SPECIFIC-HEAT OF SI(P,B) AT LOW-TEMPERATURES

The specific heat C of Si:(P,B) with carrier concentration N between 0 .8 and 17.8 x 10(18) cm(-3) and compensation ratio varying from 0.25 t o 1 was measured in the temperature range between 0.06 and 3 K and in magnetic fields up to 6 T. Above the critical carrier concentration N, of the metal-insulator transition (MIT), the linear coefficient of C varies as expected for a nearly-free-electron metal and drops rapidly for N < N-c as found previously for uncompensated Si:P. Below 1.5 K an additional contribution Delta C is found that is attributed to locali zed magnetic moments. These persist even on the metallic side of the M IT. In lar er magnetic fields Delta C develops into a Schottky anomaly . Although the overall behavior of Delta C in Si:(P,B) is again simila r to that in Si:P, some quantitative differences, e.g., in the tempera ture dependence of Delta C and the concentration of localized magnetic moments just below N-c, are observed.