ABSTRACT
Cross-sectional scanning tunneling microscopy is used to map out the potential distribution at GaAs p-n junctions with sub-nanometer resolution and to correlate the potential distribution to a simultaneously obtained dopant distribution. This allows atomic resolution identification of the metallurgical interface, the width of the depletion zone, and the electronic interface defined by the Fermi energy position as well as its pronounced roughness arising from fluctuations in the dopant atom distribution beyond statistical expectations. Furthermore, local scanning tunneling spectroscopy unveils variations in electronic characteristics of local fluctuations of the dopant atom distribution that can be explained by confining potential barriers even at room temperature. Fluctuations always present in the dopant distribution limit the achievable miniaturization of semiconductor devices, by introducing "intrinsic" variations in individual device characteristics. Although this problem is of key importance, it has turned out that a simultaneous direct experimental access to individual dopant atoms and the corresponding potential distributions is a very difficult task.
