Synchrotron light based spectroscopy of MBE-grown (GaMn)As structures

Doktorsavhandling, 2009

Structures based on the diluted magnetic semiconductor (GaMn)As have been grown by low temperature molecular beam epitaxy and studied using synchrotron radiation based electron spectroscopy. An investigation of modifications due to in situ low temperature annealing under amorphous As capping has been performed. A clear accumulation of Mn is observed. This is ascribed to a reaction between diffusing Mn interstitials and the As capping. The reacted surface is smooth and well ordered with a 1x2 reconstruction. All data indicate that the annealed (GaMn)As is terminated by a monolayer MnAs in zinc-blende structure. The good surface quality of the MnAs-terminated layer allows further epitaxial growth. As an example, it was possible to deposit a 3 ML thick MnBi film layer-by-layer. MnBi is particularly interesting in this context due to its predicted half-metal characteristics The GaAs/(GaMn)As interface has been studied with focus on the electrostatic properties. No band offset between the two systems was observed. The continuous transition is explained as an effect of electronic smearing of the atomically abrupt interface. Annealing induced diffusion of Mn interstitials through GaAs films grown on (GaMn)As during thermal treatment was also studied. It was found that GaAs layers thicker than 8 monolayers effectively hinder all Mn out diffusion. The effect was ascribed to the electrostatic potential barrier due to band bending in the GaAs film. Nanowires catalyzed by MnAs particles were studied using valence band photoemission with photon energies around the Mn2p threshold. It was found that with increasing nanowire length the resonant photoemission eventually dominated over the Auger decay channel. This was ascribed to dilution of Mn in the wires.