The Metal-Insulator Transition in Compensated Silicon

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High concentrations of donor or acceptor impurities in silicon, the omnipresent technical material of the computer age, produce a metallic system rather than a semiconductor. The characteristics of the transition from metallic to insulating properties as the impurity concentration is decreased have been of interest for many years but particularly since about 1980 as a result of a confluence of new experiments and new theories. In spite of these advances, a satisfactory description of some unusual electrical transport and magnetic properties of the classic semiconductor system, n-type silicon remains elusive. Samples of doubly-doped ("compensated") silicon are available for these studies. New theories connect a description of the electrical conductivity to unusual magnetic properties which have been observed in samples with electron concentration near the critical concentration for the transition from metal to insulator. By comparing properties of our samples of compensated silicon with those of uncompensated silicon, a test of the validity of current theory is possible. These properties will be measured to make that test.