Characterization of arsenide/phosphide heterostructure interfaces by scanning tunneling microscopy

We have used cross-sectional scanning tunneling microscopy (STM) to study interface structure in arsenide/phosphide heterostructures grown by gas-source molecular beam epitaxy. High-resolution images of a sample grown at 550°C and consisting of GaAs interrupted at 200 Å intervals with a 40 s P2 flux reveal phosphide interlayers as wide as 30 Å and exhibiting lateral variations in structure over nanometer length scales. A similar sample grown at 450°C exhibits narrower interlayers and a lower level of phosphorus incorporation. Data obtained by STM have been corroborated by data from high-resolution X-ray diffraction (HRXRD) and reflection high-energy electron diffraction (RHEED) studies. Together, these studies provide direct information about nanometer-scale grading and lateral nonuniformity of interfaces that can occur under these growth conditions.