Controlled introduction of defects in GaMnAs and GaBeAs thin films by ion-beam irradiation*

The existence of interstitial Mn atoms, and other point defects, significantly modify magnetic and transport properties of Ga$_{\mathrm{1-x}}$Mn$_{\mathrm{x}}$As. This opens a door to manipulate these properties in a controlled way by ion-beam irradiation of thin films. We study how the simultaneous lowering of hole concentration and increasing of disorder, introduced by ion-beam irradiation, affects the magnetization and conductivity of Ga$_{\mathrm{1-x}}$Mn$_{\mathrm{x}}$As samples [1,2]. Highly doped Ga$_{\mathrm{1-x}}$Be$_{\mathrm{x}}$As is a material that can be produced with similar doping levels but that shows no ferromagnetism, acting as an interesting experimental standard for comparison of transport properties of Ga$_{\mathrm{1-x}}$Mn$_{\mathrm{x}}$As. We irradiate Ga$_{\mathrm{1-x}}$Mn$_{\mathrm{x}}$As and Ga$_{\mathrm{1-x}}$Be$_{\mathrm{x}}$As thin films with 2 MeV oxygen ion beams. Samples were grown by molecular beam epitaxy. Sheet resistance of the thin films was measured in situ in the irradiation chamber as a function of the incident dose.\\[4pt] [1] E. H. C. P. Sinnecker et al., Phys. Rev. B. 81, (2010) 245203.\\[0pt] [2] M. M. Sant'Anna, et al., Meth. in Phys. Res. B. 273 (2012) 72.