Investigation of defect levels in semi-insulating materials by modulated and transient photocurrent: comparison of methods

High-resolution photoinduced transient spectroscopy and the modulated photo current technique are compared in terms of possible application to the inve stigation of defect levels in semi-insulating monocrystalline materials. Af ter a description of the theoretical and experimental aspects, the advantag es, drawbacks and limitations of each method are discussed. The two techniq ues complement each other and their potentialities are exemplified by the m easurements of trap parameters in the same samples of semi-insulating Cr-do ped and undoped GaAs. From these results we deduce a possible model for the properties of the Cr defect in GaAs.