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HL: Fachverband Halbleiterphysik

HL 17: Poster I

HL 17.43: Poster

Montag, 25. Februar 2008, 16:30–19:00, Poster D

Post growth annealing behaviour and carrier concentration of Ga_1−xMn_xAs grown on (001), (311) and (110) GaAs substrates — •Michael Hirmer, Ursula Wustbauer, Dieter Schuh, and Werner Wegscheider — Institut für Experimentelle und Angewandte Physik, Universität Regensburg, Germany

We present a detailed study of post-growth annealing experiments of thin Ga_1−xMn_xAs films grown by low temperature molecular beam epitaxy. The films were grown on (001), (311) and (110) semi-insulating GaAs substrates with layer thickness ranging from 5 to 300nm. Since the ferromagnetism of this Zener-like diluted magnetic semiconductor is hole-mediated, the ferromagnetic transition temperature T_C can be increased corresponding to T_C ∝ x_effp^1/3 (x_eff: effective Mn concentration, p: carrier density) by post growth annealing. This reduces the Mn-interstitial lattice defects, which act as double donors and couple antiferromagnetically with substitutional Mn, thereby suppressing the ferromagnetism. As a result, we have increased T_C by annealing at about 200^∘C in air to 167K. To improve the process, we monitored the resistance in situ and identified negative annealing-effects, which were more distinctive with higher As:Ga ratio during growth. The out-diffusion of Mn_I is strongly dependent on growth direction, annealing temperature and the passivation process on the surface. To estimate the Mn_I content and get the enhancement of carrier concentration (p), we calculated p from high magnetic field Hall measurements before and after annealing. The changes in the measurements suggest that the anomalous Hall-effect is not only caused by scattering processes.