New properties associated with selective substrate removal have been observed in the application of this technique to GaAs thin film compliant substrates. Citric acid- and NH4OH-based etches are used to selectively etch the GaAs substrate and stop on an AlAs layer. The AlAs stop-etch layer is transformed into a layer that is almost twice as thick as the original layer, mismatched to the remaining GaAs epilayer, and has a refractive index around 2.0. Replacement of the single AlAs stop etch layer with multiple thin AlGaAs stop etch layers is proposed to alleviate this problem.