Metal-insulator transition in the compensated semiconductor Si:(P,B)

The results of a continuing investigation of the effects of impurity compensation on the characteristics of the metal-insulator (M-I) transition in Si:P are reported. The system used is Si:(P,B). Most of the information is derived from measurements and analysis of the dc electrical conductivity {σ} in the temperature range 50 mK T4 K. The form of the temperature dependence of {σ} in this range is extensively studied. For samples with electron concentration n near nc, the critical concentration for the M-I transition, the temperature dependence of {σ} departs significantly from the form {σ}={σ}(0)+mT1/2+BT3/4, which describes samples at higher values of n. As K, the ratio of acceptor to donor concentration, is increased from zero, the value of nc first decreases slightly before rising sharply at larger values of K. Measurements of {σ}(0) as a function of n in uncompensated Si:P agree with data in the literature. The applicability of the scaling theory to a description of our measurements of {σ}(0) as a function of n in compensated samples is questioned. Attention is given to establishing the most reliable methods for determining values of impurity concentrations.