Modification of GaAs by Mn ion implantation towards semiconductor spintronic thin films

Ferromagnetic semiconductors with high Curie temperatures and large coercivity are very promising materials for spintronic applications. An approach to fabricate ferromagnetic GaMnAs is Mn ion implantation into GaAs followed by pulsed laser annealing (PLA) [1]. Magnetic Mn ions which occupy the Ga sublattice sites form acceptor centers and pro-vide free holes for the mediation of the parallel align-ment of the magnetic moments of the Mn ions. For a strong ferromagnetic interaction, activation of the Mn acceptor dopants over their thermodynamic equilib-rium solubility is necessary. Long time, rapid thermal, and also flash lamp annealing processes take too long to realize a large enough free hole concentration by activation of Mn acceptor dopants. From a thermody-namical point of view, the PLA process is beside the more expensive LT-MBE process the best route to fabricate oversaturated ferromagnetic GaMnAs.
We investigated the influence of the implanted Mn concentration and PLA conditions on the structural and magnetic properties of GaMnAs thin films. We per-formed heatflow calculations to visualize the fast tem-peratue quenching during the PLA process [2]. Using SQUID magnetometry, we reveal a strong decrease of the saturation magnetization with increasing number of laser pulses during PLA (Fig. 1). However, the crystal-line quality is improved after several laser pulses. This has been verified by RBS (Fig. 2) and XRD measure-ments. The decrease of saturation magnetization after several laser pulses may be caused by the continuous Mn cluster formation during each PLA cycle.
[1] M. A. Scarpulla. et al. APL 82 (2003) 1251
[2] D. Bürger et al. PRB 81 115202 (2010)