As characteristic dimensions in semiconductor devices continue to shrink and as advanced heterostructure devices increase in prominence, the ability to characterize structure and electronic properties in semiconductor materials and device structures at the atomic to nanometer scales has come to be of outstanding and immediate importance. Phenomena such as atomic-scale roughness of heterojunction interfaces, compositional ordering in semiconductor alloys, discreteness and spatial distribution of dopant atoms, and formation of self-assembled nanoscale structures can exert a profound influence on material properties and device behavior. The relationships between atomic-scale structure, epitaxial growth or processing conditions, and ultimately material properties and device behavior must be understood for realization and effective optimization of a wide range of semiconductor heterostructure and nanoscale devices.
Cross-sectional scanning tunneling microscopy (STM) has emerged as a unique and powerful tool in the study of atomic-scale properties in III-V compound semiconductor heterostructures and of nanometer-scale structure and electronic properties in Si micro-electronic devices, offering unique capabilities for characterization that in conjunction with a variety of other, complementary experimental methods are providing new and important insights into material and device properties at the atomic to nanometer scale. In this article, we describe the basic experimental techniques involved in cross-sectional STM and give a few representative applications from our work that illustrate the ability, using cross-sectional STM in conjunction with other experimental techniques, to probe atomic-scale features in the structure of semiconductor heterojunctions and to correlate these features with epitaxial-growth conditions and device behavior.