Infrared Cyclotron Resonance and Related Experiments in the Conduction Band of InSb

We present a comprehensive study of the conduction band of InSb. Experimental observations of fundamental cyclotron-resonance transitions involving the lowest Landau levels and both spin states are reported over a range of magnetic fields from 5 to 35 kG. Additional transitions involving impurities, phonons, cyclotron-resonance harmonics, and spin flip are also observed. The fundamental cyclotron resonance and the spin-flip cyclotron resonance, together with the spin-resonance results of Isaacson, are analyzed in terms of a nonparabolic band theory involving interactions with the six valence bands and allowing the possibility of interactions with more remote bands. A good fit to the nonparabolic band theory is obtained when one is careful to remove effects due to impurities and the electron-phonon interaction. A band-edge effective mass of $0.0139m$ and a band-edge $g$ factor of -51.3 are obtained. An analysis using these values shows that remote band interactions contribute to the value of either the mass or $g$ factor or both by an amount on the order of 10%. The transition energies for cyclotron-resonance harmonics, spin-flip transitions, phonon-assisted cyclotron resonance, and spin resonance as a function of Fermi level have been calculated and give a good fit to the data. This confirms the identification of these transitions and shows that the nonparabolic theory gives the magnetic energy levels correctly to energies as high as 60 meV. A value of 24.4 meV is found for the LO phonon energy. The existence of the phonon-assisted cyclotron resonance is explained on the basis of the mixing of Landau levels by the electron-phonon interaction. The strength of the cyclotron-resonance harmonics is not satisfactorily explained, although several possible mechanisms are proposed. An $H=0\mathrm{}$ electron-energy dispersion relation and other related band properties are deduced from the magnetic field results and compared with other experiments.