Nanoprobing of semiconductor heterointerfaces: quantum dots, alloys and diffusion

Interfaces play a key role in the performance of electronic, optoelectronic and photovoltaic devices. Within epitaxial semiconductor heterostructures, interfaces are commonly characterized using various methods including transmission electron microscopy, secondary ion mass spectroscopy, x-ray diffraction, photoluminescence spectroscopy and capacitance-voltage profiling. The averaging present in these conventional techniques limits their ability to resolve critical atomic-scale features. In addition, many of these methods require detailed modelling in order to determine quantitative interface profiles. Thus, these techniques are often not suitable for obtaining the localized information needed to elucidate the structure and properties of heterointerfaces. Alternatively, nanoprobing of heterointerfaces using cross-sectional scanning tunnelling microscopy (XSTM) has emerged as a powerful method for resolving atomic features at interfaces within heterostructures. In this paper, we describe XSTM and discuss its application to several important issues in semiconductor heterostructure materials, including the formation and ordering of quantum dot arrays, direct measurements of interdiffusion and segregation lengths and investigations of the mechanisms of alloy phase separation. (topical review)