Enhancement of Curie temperature in Ga(1-x)Mn(x)As/Ga(1-y)Al(y)As ferromagnetic heterostructures by Be modulation doping

摘要

The effect of modulation doping by Be on the ferromagnetic properties ofGa(1-x)Mn(x)As is investigated in Ga(1-x)Mn(x)As/Ga(1-y)Al(y)As heterojunctionsand quantum wells. Introducing Be acceptors into the Ga(1-y)Al(y)As barriersleads to an increase of the Curie temperature T_C of Ga(1-x)Mn(x)As, from 70 Kin undoped structures to over 100 K with the modulation doping. This increaseis qualitatively consistent with a multi-band mean field theory simulation ofcarrier-mediated ferromagnetism. An important feature is that the increase ofT_C occurs only in those structures where the modulation doping is introducedafter the deposition of the magnetic layer, but not when the Be-doped layer isgrown first. This behavior is expected from the strong sensitivity of Mninterstitial formation to the value of the Fermi energy during growth.