NUCLEAR MICROSCOPY OF GAAS/SI HETEROSTRUCTURES

Nuclear microprobe analysis allows PIXE, RBS and channeling analysis of structures as small as a few 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 50 x 50-mu-m2 in size. The epitaxial GaAs layers in the trenches were found to be of reasonable quality, with chi-min 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-mu-m. 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.