Landau-level spectra of conduction electrons at an InAs surface

I report magneto-oscillatory effects in tunneling through InAs-oxide-Pb junctions, which reflect the Landau levels of conduction electrons near the InAs-oxide interface. These oscillatory effects, which have been observed in transverse as well as longitudinal magnetic fields, are understood in terms of a qualitative theoretical picture. From the longitudinal magneto-oscillations, we have obtained that the effective cyclotron mass $\frac{{m_0}^{*}}{m}=0.0215\mathrm{}\pm 0.0005$ at the conduction-band edge and that, at energies within 400 meV above the band edge, it increases linearly with increasing energy at a rate of 1.2×${10}^{-4\mathrm{}}$/meV. This value of ${m_0}^{*}$ is ∼ 7% smaller than that obtained from cyclotron resonance and magneto-phonon experiments on bulk InAs. The transverse magneto-oscillations are identified with Landau levels of electrons whose cyclotron orbits graze the oxide potential barrier. The level broadening $\Gamma$, as deduced from the magnetic field dependence of the oscillation amplitude, corresponds to a relaxation time ∼ ${10}^{-14\mathrm{}}$ sec. Within our experimental uncertainties, $\Gamma$ increases linearly with increasing excitation energy.