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Scanning tunneling microscopy for semiconductor carrier profiling is simulated in three dimensions. By solving the tunnel currents between a probe tip and a sample consistently with the current continuity equations, current-voltage characteristics in good agreement with measurements are obtained. Critical differences from potential-based calculations are observed under depletion and inversion conditions. By preparing a current-concentration table from samples with uniform concentrations, the carrier profile in p-n junction samples can be extracted by estimating the concentrations at each position. It is revealed that the tunnel current is spread around the depletion region of a p-n junction, which affects the results dramatically. When a proposed simulation is iteratively used with measurements, impurity profile extraction is possible even in the depletion region. [ABSTRACT FROM AUTHOR]

Chalcogenide superlattice (SL) phase-change memory materials are leading candidates for non-volatile, energy-efficient electric memory where the electric conductance switching is caused by the atom repositioning in the constituent layers. Here, we study the time evolution of the electric conductance in [(GeTe)2/(Sb2Te3)1]4 SLs upon the application of an external pulsed electric field by analysing the structural and electrical responses of the SL films with scanning probe microscopy (SPM) and scanning probe lithography (SPL). At a low pulse voltage (1.6-2.3 V), a conductance switching delay of a few seconds was observed in some SL areas, where the switch to the high conductance state (HCS) is accompanied with an SL expansion under the strong electric field of the SPM probe. At a high pulse voltage (2.5-3.0 V), the HCS current was unstable and decayed in a few seconds; this is ascribed to the degradation of the HCS crystal phase under excessive heating. The reversible conductance change under a pulse voltage of opposite polarity emphasised the role of the electric field in the phase-transition mechanism.