Repeatability of Si concentration measurements in Si-doped GaN films

In high mass resolution secondary ion mass spectrometry Cs+ depth profile measurements of Si in GaN films, the secondary ion intensity ratio of Si-28(-) to the matrix Ga-69(-) signal has been observed to be poorly repeatable from measurement to measurement. In some cases the Ga-69(-) signals from adjacent areas showed different intensity levels even though the Si-28(-) intensities were similar. Variation of the Ga-69(-) matrix signal from run to run creates a large uncertainty in the determination of the Si concentration in a GaN film when a relative. sensitivity factor is used. The changes in Ga-69(-) intensity from repeat measurements have been determined to be affected by the instrument vacuum condition, ion energy distribution, sample charging, and type of sample holder used in the measurement. (C) 1997 American Vacuum Society.