We have measured infra-red cyclotron resonance in epitaxial thin films of indium arsenide on semi-insulating gallium arsenide and bulk indium arsenide substrates. A novel feature is that the crystal quality and perfection of thin films is found to be better than the best available bulk specimens as indicated by the observation of clear, narrow cyclotron absorptions.
By a study of the magnetic absorption at different temperatures we have separated effects due to cyclotron resonance spin up, spin down and impurity resonance. Theoretical extrapolation of results yields a low field, zero k-vector effective mass for conduction band electrons in InAs of m* = (0·0230±0·0003)m0. Information on the impurity binding energy is presented.
Our two-phonon absorption measurements also provide accurate values of ωTO = 215·5±3 cm−1 ωLO = 241·8±3 cm−1.
Evidence of resonant electron-phonon (polaron) coupling in InAs, of similar nature to that previously reported for InSb, is shown by comparison with theoretically predicted absorption peak positions, effective masses and half widths and has yielded an estimate of Fröhlich coupling constant of α = 0·05±0·01.
The use of such epitaxial layers for optical measurements has been extended to GaAs. Microwave 2 mm cyclotron resonance has been observed in a thin epitaxial film of GaAs yielding an electron effective mass of m* = (0·068±0.002)m0.