We analyze the quantized states of the tip-induced quantum dot appearing in scanning tunneling spectroscopy ͑STS͒ on n-type InAs͑110͒ (N D ϭ2ϫ10 16 cm Ϫ3 ). STS at negative sample bias ͑Ϫ200-0 mV͒ is used to determine the state energies. The analysis of the spectra indicates that the z-quantization leads to one or two quantized states while a ladder of states due to the lateral confinement is observed. The magnetic-field dependence ͑0-6 T͒ shows the expected splitting of the first excited state in quantitative agreement with Hartree calculations. If an ionized dopant is located in the center of the quantum dot, a reduction in energy and a change in intensity of the single-particle ground state is found, which is also in quantitative agreement with Hartree calculations. The analysis of the tip-induced states can be used to reconstruct the shape of the tipinduced band bending. ͓S0163-1829͑99͒03511-0͔
We present a new design of a low-temperature ultrahigh-vacuum (UHV) scanning tunneling microscope setup with a combination of a solenoid and a split-pair magnet. The scanning tunneling microscope can be operated at temperatures down to 8 K and in a rotatable magnetic field of up to 1 T. Magnetic fields of up to 7 T perpendicular and 2 T parallel to the sample surface can be applied. The UHV part of the system allows in situ preparation and low energy electron diffraction/Auger analysis of samples. First topographic and spectroscopic measurements on p-InAs(110) are presented.
Scanning tunneling spectroscopy images on n-InAs(110) exhibit a strong magnetic field dependent contrast on the 50 nm length scale, indicating fluctuations in the density of states of the sample. The contrast is correlated to previously observed Landau oscillations in dI/dV curves. Its origin is a spatial fluctuation of the Landau level energy of 3-4 meV caused by the inhomogeneous distribution of dopant atoms. Besides inducing large-scale fluctuations in the density of states, dopants preserve their ability to scatter electron waves. The resulting wave pattern is found to depend on the magnetic field. It is suggested that the dependence is guided by the condensation of the electronic states on Landau tubes.
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