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The advances in cross-sectional scanning tunneling microscopy and spectroscopy (XSTM/XSTS) are reviewed with emphasis on the structural and spectroscopic studies of semiconductor heterostructures on an atomic or nanometer scale. The un paralleled chemical and electronic sensitivities as well as spatial resolution of XSTM/XSTS are addressed. Examples shown here include recent results of cation/anion selective imaging, observations of individual impurities, interface roughness and asymmetry, band offset determination, and nanometer-resolution band mapping in prototype (AlGa) As/GaAs low-dimensional multilayered systems. Current developments in use of XSTM/XSTS combined with other techniques for the exploitation of optical properties of semiconductor heterostructures are also discussed.
We have reviewed the recent developments of XSTM/XSTS and some related XSPM/XSPS techniques for the structural, electronic, and optical studies of semiconductor heterostructures.Although most of the examples presented herefocus on the (AlGa) As/GaAs system because of its importance for optoelectronic and quantum device applications, the XSTM/XSTS technique is readily applicable for the investigation of other material systems. Because of its extremely high sensitivities in analyses of structural and electronic properties, XSTM/XSTS has now become a powerful technique both for imaging low-dimensional structures such as quantum wells and quantum wires and for performing spectroscopic investigations on individual quantum structures.

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Usint experimental profiles for the radial beam-plasma parameters and electron impact ionization cross-section data, the neutral-to-ion conversion factors (NICF), α⁰_M are determined for a selection of elements M in a new type of secondary-neutralmass-spectrometer called SNART (Sputtered Neutral Analysis Riken Type). Signal loss due to the curvature of the ion trajectories across the source magnetic field is taken into account. A comparison between the relative NICF's, α⁰_M/α⁰_Fe, and machine measured relative sensitivity factors D⁰_M/ D⁰_Fe is made. Results show the potential for quantitative analysis of insulating materials in SNART.

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