Nondestructive measurement of indium content in semi-insulating GaAs substrates and ingots

We report the use of room-temperature photoluminescence to determine low levels of indium in semi-insulating GaAs intended for use as low dislocation material for substrates of integrated circuits. We have compared this technique with other optical methods such as low-temperature (4.2 K) photoluminescence and Raman scattering and find it more convenient for this application. Room-temperature photoluminescence easily allows measurement of In content in In_xGa_1-xAs in the range of 0.1-2% with a standard deviation of 0.1%, which is sufficient for most practical applications. The technique is nondestructive and rapid. The measurement can be done on polished, sawed, or etched surfaces, or on side surfaces of as-grown ingots without any treatment. To illustrate its use, we have measured variations in the In content of semi-insulating GaAs due to segregation of In in the melt during liquid encapsulated Czochralski growth.