Mechanism for heavy Fe doping of epitaxial GaAs/AlGaAs heterostructures

Heterostructures which are maximally doped with iron and which contain bulk layers of GaAs and AlxGa1-xAs, as well as GaAs/AlGaAs superlattices are grown on an EP-1302 molecular-beam epitaxy system. An analysis of secondary-ion mass spectrometry profiles of the iron penetration shows that during growth on substrates oriented in the [100] plane, the maximum concentrations of iron in the GaAs layers, as well as in the GaAs/AlGaAs superlattices, are two orders of magnitude below those for the ternary solution AlGaAs. A radical enhancement in the maximum Fe concentration (up to 5X10(18) cm(-3)) in GaAs/AlGaAs superlattices can be attained by growing them on substrates cut with a 3 degrees deviation from the [100] plane. It is important that at these high doping levels the low-temperature (10 K) absorption and photoluminescence spectra of the superlattices still contain narrow exciton lines. Possible mechanisms for the selective implantation of iron in GaAs/AlGaAs hetrostructures are analyzed. (C) 1999 American Institute of Physics. [S1063-7826(99)01003-0].