Wavelength- and material-dependent absorption in GaAs and AlGaAs   microcavities
  The quality factors of modes in nearly identical GaAs and Al_{0.18}Ga_{0.82}As microdisks are tracked over three wavelength ranges centered at 980 nm, 1460 nm, and 1600 nm, with quality factors measured as high as 6.62x10^5 in the 1600-nm band. After accounting for surface scattering, the remaining loss is due to sub-bandgap absorption in the bulk and on the surfaces. We observe the absorption is, on average, 80 percent greater in AlGaAs than in GaAs and in both materials is 540 percent higher at 980 nm than at 1600nm. 
C. P. Michael, K. Srinivasan, T. J. Johnson, O. Painter, K. H. Lee, K.   Hennessy, H. Kim, E. Hu