Stoichiometry and absolute atomic concentration profiles obtained by combinedRutherford backscattering spectroscopy and secondary-ion mass spectroscopy:InAs nanocrystals in Si

Abstract

Rutherford backscattering spectroscopy (RBS) and secondary-ion massspectroscopy (SIMS) were combined to achieve depth profiling calibrated inabsolute atomic concentrations. This method was applied to InAs nanocrystals,grown by molecular beam epitaxy (MBE), buried in a Si matrix. By means ofRBS, with its capability of accessing the buried layers, we determined thedepth-integrated areal densities of As and In. These were used to calibratethe SIMS profiles with their high depth resolution and dynamic range inabsolute atomic concentrations. This allowed us to identify, besides a wellconfined layer of stoichiometric InAs nanocrystals, significant diffusion of Inand As into the Si matrix in despite of their larger atomic radii, and anexcess of As due to its non-reactive deposition on Si from the excess As4flux during the MBE growth. On the basis of these findings, we suggestmeasures to optimize the MBE process for InAs/Si and similar systems.