METAL-INSULATOR-TRANSITION IN HEAVILY DOPED INDIUM-ANTIMONIDE SUBJECTED TO A MAGNETIC-FIELD

A qualitative treatment is given of the metal-insulator transition induced in heavily doped n-type InSb by a magnetic field. The treatment is based on an analysis of the results of galvanomagnetic and acoustic measurements at temperatures 0.05-20 K using magnetic fields up to 60 kOe and ultrasound of frequency 100-200 MHz. The nature of the transition was found to be different in weakly and strongly compensated materials. The transition in a weakly compensated (K < 0.5) n-type InSb was due to the localization of electrons at individual impurity centers (magnetic freezeout effect). The application of a magnetic field to strongly compensated (K = 0.7-0.8) n-type InSb first resulted in localization of electrons in wells of a large-scale potential, associated with fluctuations of the impurity concentration. This gave rise to metallic droplets which were not connected. An increase in the magnetic field fragmented the drops and this was accompanied by the localization of electrons: both inside the drops and at the Fermi level. Finally, in the case of samples with a very high degree of compensation (K > 0.9) the Fermi level was located so low in an allowed band that electrons were localized once more in a small-scale potential, in the same way as in lightly doped strongly compensated samples.