Nuclear microscopy of GaAs/Si heterostructures

Nuclear microprobe analysis allows PIXE, RBS and channeling analysis of structure as small as few a micrometres in size. The present work compares results from H+ and He+ microprobes which were used to analyse epitaxial GaAs heterostructures grown in trenches cut through a surface oxide layer on a (001) oriented Si wafer. Conventional broad-beam analysis was not possible because of the scale of the trenches, which had dimensions less than 50x50 μm2 in size. The epitaxial GaAs layers in the trenches were found to be of reasonable quality, with χmin of 27% (for He+ channeling) at the near surface, rising to 77% (for H+ channeling) at the interface with the substrate. The layers were found to be laterally uniform to the probe resolution of 1 μm. The results also indicated that fabrication techniques resulted in a GaAs layer forming over the oxide which was thinner than over the single crystal Si in the trenches and probably contained either interdiffused Si or pinholes. (orig.)