Comparative study of Mn and Fe incorporation into GaN by metalorganic chemical vapor deposition

Wide bandgap diluted magnetic semiconductors (DMS) have been of interest recently due to theoretical predictions of room temperature ferromagnetism in these materials. However, the mechanism of the observed ferromagnetism of the nitrde-based DMS is still controversial, and may originate from a carrier-mediated, defect-related or nanoscale clustering mechanism. In this work, we present a comparative study of the incorporation of various transition metals and their effect on the optical, structural, and magnetic properties of GaN. Metal-organic chemical vapor deposition (MOCVD) has been employed to produce epitaxial films of varying thickness and manganese and iron concentrations using bis-cyclopentyldienyl (magnanese, iron) as the transition metal sources. High-resolution X-ray diffraction reveals no macroscopic secondary phases under optimized growth conditions. Magnetic hysteresis is observed at room temperature in both Ga1-xMnxN and Ga1-xFexN, though the strength of the magnetic ordering is roughly an order of magnitude weaker in the Fe-alloyed samples. Increasing Mn concentrations significantly affects the long-range lattice ordering, and the observation of local vibrational modes (LVMs) supports the formation of nitrogen vacancies, even under optimized MOCVD growth conditions. Such vacancies form shallow donor complexes and thus contribute to self-compensation. Disorder-induced modes at 300 cm(-1) and 7 10 cm(-1) and a LVM due to vacancies at 669 cm(-1) were revealed by Raman spectroscopy. The iron-doped samples also show the disorder-induced modes, but the vacancy-related mode is not observed which is attributed to Fermi level and defect formation energy considerations. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.