Storage Conditions for High-Accuracy Composition Standards of AlGaAs

AlGaAs epitaxial films were stored under different environmental conditions and the resulting surface oxidation and contamination variations measured with several analytical techniques. Auger depth profiles confirmed that contamination had been confined to within approximately 10 nm of the surface for all specimens stored in controlled environments for over three years. We also performed an atomic force microscopy study on a multilayer structure, measuring the height of the oxides formed in air. Surface contamination was examined in more detail with time-of-flight secondary ion mass spectrometry and x-ray photoelectron spectroscopy. Surface oxides changed over time, and could be altered by sputtering. Sputtering was particularly effective in removing hydrocarbons. Based on these results, AlGaAs reference films for x<0.4 should remain stable for at least five years if stored in either nitrogen or vacuum environments, with allowance for periodic handling in air.