METALLIC IMPURITY BAND IN THE NARROW-BAND-GAP SEMICONDUCTOR N-TYPE INSB

Magnetotransport and far-infrared laser spectroscopy have been combined to probe the nature of the impurity band in the vicinity of the magnetic-field-induced metal-insulator transition. The spectroscopic results obtained in n-type InSb show the persistence of the impurity cyclotron resonance, (000) --> (110), through the metal-insulator critical field which is determined by the transport measurement. This first observation in the narrow-band-gap semiconductor together with the earlier results of n-type GaAs reported by Romero et al. provides strong evidence for the existence of a metallic impurity band, split off from the conduction band, and this may be a universal feature of the metal-insulator transition occurring in doped semiconductors regardless of their gap properties.