Measurement of the chromium concentration in semi-insulating GaAs using optical absorption

Chromium has been observed to be responsible for a band of absorption in semi-insulating GaAs. The corresponding absorption coefficient has been carefully calibrated using three different chemical analysis methods. It is shown that the spatial distributions of Cr in semi-insulating GaAs ingots can be obtained very easily using optical absorption measurements and that the segregation coefficient of Cr in GaAs is equal to 8.9×10−4. The nature of the optical transitions due to the presence of Cr is discussed in detail and it is shown that they occur mainly on the Cr3+ in semi-insulating material.