quantum wells

ture of 400◦C. Electrical and structural measurements demonstrate that this elevated temperature reduces As defects while allowing the substitutional incorporation of Mn into Ga sites. From a combination of Hall and secondary ion mass spectroscopy measurements we estimate that at least 70-90% of the Mn incorporates substitutionally in all samples studied. The incorporation behavior shows both a substrate temperature and QW width dependence. The low defect density of these heterostructures, compared to typical lower temperature grown GaMnAs, enables the observation of both polarization-resolved PL and coherent electron spin dynamics, from which the conduction band exchange parameter is extracted. No evidence of long-range Mn spin coupling is observed, whereas negative effective Curie temperatures indicate spin heating due to photoexcitation. Light Mn-doping maximizes the electron spin lifetime indicating the importance of the Dyakonov-Perel de- coherence mechanism in these structures. PL spectra reveal a low energy peak from shallow donors, which because of the paramagnetic behavior of its PL polarization, we ascribe to Mn interstitials.