Determination of Mn Acceptor Compensation in MBE-Grown GaMnAs via Magnetic Circular Dichroism (MCD)

In order to investigate the origin of the magnetic circular dichroism (MCD) in Ga_1-xMn_x As, we prepared a series of paramagnetic samples with a very low Mn content (x~0.0005 and 0.0003), grown at different substrate temperatures. The samples grown at low temperatures (< 300 degC) show a sign change in the MCD, while those grown at higher temperatures (>300degC) reveal broad positive MCD spectra similar to those observed in ferromagnetic Ga_1-xMn_xAs. In addition, samples grown at high temperature ( ~600 degC) but with Si co-doping show a behavior typical to samples grown at low substrate temperatures, namely sign changing MCD spectra. Our results indicate that the negative component of the MCD does not originate from the interband transitions but from transitions involving ionized Mn acceptors