Infrared Spectroscopy of Ge:Mn Thick Films Prepared by Ion Implantation and Post-annealing
Obied, Laila Hassan
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An infrared transmission study of Ge:Mn systems is presented in this work. Various Ge:Mn samples have been prepared by both single (Mn2+ ion energy 4.76 MeV, dose 2x10^16 /cm^2) or multiple (dose 1x10^16 /cm^2) into high resistivity (100) Ge substrates. Both conventional and flash lamp annealing procedures have been used to prepare a set of samples that were characterized by X-ray Diffraction (XRD), Secondary Ion Mass Spectrometry (SIMS) and magnetometry as well as infrared transmission spectroscopy (60-8000 cm^-1). After implantation, the Ge:Mn layers are about 3 mm thick and amorphous as revealed by XRD. Samples conventionally annealed at temperatures below 250C maintained their amorphous structure. Samples annealed at temperature above 330C recrystallized into a polycrystalline structure. SIMS measurements show that the diffusion of Mn is greatly affected by the starting distribution and that diffusion is much higher in samples prepared with the lower total Mn dose. The presence of multiple magnetic phases in all the annealed samples was indicated by field and temperature dependent measurements of the total moment. Our diverse preparations suggest that the formation of secondary phases in Ge:Mn system in unavoidable. Magnetic measurements suggest that the maximum volume fraction of metallic Mn5Ge3 inclusions is of the order of 1x10^-3, much lower than the percolation threshold of metallic inclusions in an insulating matrix. Infrared transmission measurements on the same samples show the presence of a low frequency Drude like absorption with high hole concentration (p~10^ 18 /cm^3) which is greater than the critical density for metal-insulator (MI) transition in Ge. This observation suggests Mn has crystallized in substitutional sites to a far greater degree than was achieved with traditional equilibrium crystal growth. The MI transition has been investigated in the Ge:Mn system by studying the temperature dependent transmission between 4K and 300K and comparing to similar measurements on a sample of Ga-doped Ge with p = 1.5x10^16 /cm^3 which is on the insulating side of the MI transition. Finally, absorption was observed that may possibly be attributed to Mn5Ge3 inclusions in the Ge:Mn matrix.