Infrared survey of the carrier dynamics in III-V digital ferromagnetic heterostructures

Abstract

We report on the electromagnetic response of digital ferromagnetic heterostructures (DFH): systems with $\ensuremath{\delta}$-doped MnAs layers separated by GaAs spacers of variable thickness $(y)$. The gross features of the infrared conductivity of DFH samples are consistent with the notion that these digital structures are $\mathrm{Ga}\mathrm{As}∕{\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As}$ superlattices. This conclusion is supported by a combination of spectral weight analysis and effective medium theory. The optical properties of DFH also provide insights into the evolution of their critical temperature with GaAs spacing. In DFH a low-lying gap materializes in the energy dependent conductivity, which is interpreted as a mobility gap resulting from Anderson localization.