Diffusion of Mn in GaAs studied by quantitative time-of-flight secondary ion mass spectrometry

摘要

Diffusion coefficients and the activation energy for Mn diffusion in ion-implanted and layered epitaxial structures of Ga_(1-x)Mn_xAs/GaAs are reported from quantitative time-of-flight secondary ion mass spectrometry. Samples are annealed between the growth temperature (as low as 200 ℃) and approximately 400 ℃. This temperature range is reported to improve the Curie temperature, which is important for the spintronic applications of these materials. Quantitative diffusion information is obtained by calibrating the Mn concentration to ion-implanted standards and the depth scale to profilometry measurements. Depth profiles obtained for ion-implanted Mn in GaAs at a dose of 1.35×10~(15) atoms/cm~2 show increased Mn concentration within the top 5 nm of the sample but otherwise reveal no significant differences in the implantation shape after annealing up to 350 ℃. For a higher implantation dose of 8.10×10~(15) Mn atoms/cm~2, diffusion is initiated after annealing at 300 ℃ with more significant diffusion at higher temperatures. The analysis of annealed epitaxial films of even higher concentration (Ga_(0.89)Mn_(0.11)As) exhibits diffusion at all temperatures measured (200-400 ℃) and an activation energy of 0.67 ± 0.09 eV is calculated by fitting the profiles to an error function.