TY  - JOUR
AU  - Talut, G.
AU  - Grenzer, J.
AU  - Reuther, H.
AU  - Shalimov, A.
AU  - Baehtz, C.
AU  - Novikov, D.
AU  - Walz, B.
AU  - DESY
TI  - In situ observation of secondary phase formation in Fe implanted GaN annealed in low pressure N<sub>2</sub> atmosphere
JO  - Applied physics letters
VL  - 95
SN  - 0003-6951
CY  - Melville, NY
PB  - American Institute of Physics
M1  - PHPPUBDB-12678
SP  - 232506
PY  - 2009
N1  - © American Institute of Physics 
AB  - The formation of secondary phases in Fe implanted GaN upon annealing in low pressure N<sub>2</sub>-atmosphere was detected by means of in situ x-ray diffraction and confirmed by magnetization measurements. A repeatable phase change from Fe<sub>3</sub>N at room temperature and Fe<sub>3</sub>−<sub>x</sub>N at 1023 K was observed in situ. The phase transformation is explained by the change of lattice site and concentration of nitrogen within nitrides. The diffusion of Fe toward sample surface and oxidation with increasing annealing cycles limits the availability of secondary phase and hence the repeatability. At high temperature GaN dissolves and Ga as well as Fe oxidize due to presence of residual oxygen in the process gas. The ferromagnetism in the samples is related to nanometer sized interacting Fe<sub>3</sub>−<sub>x</sub>Ncrystallites.GaN is a wide band gap semiconductor that has been studied intensively in the last years because of its potential field of applications like in optoelectronics, plasmonics, as well as for high power electronics. By doping with transitional metals like Fe it might also be a diluted magnetic semiconductor (DMS) with a Curie temperature above room temperature (RT) and could then be used for spintronics.1 There are many experimental studies reporting ferromagnetism at RT in Fe doped GaN. In a real DMS, with magnetic atoms randomly substituting cation sites, ferromagnetic coupling is supposed to be due to the indirect exchange coupling between magnetic impurities mediated by holes.1–4 Experimental observation of strong-coupling effects in a DMS Ga<sub>1</sub>−<sub>x</sub>Fe<sub>x</sub>Nwas reported by Pacuski et al.5 Robust ferromagnetism in the region of insulator-to-metal transition was predicted for high hole densities. However, there are also other possible sources of ferromagnetism like spinodal decomposition of Fe or ferromagnetic secondary phases. The detection of those is rather difficult. Bonanni et al.6 prepared GaN:Fe layers by metalorganic chemical vapor deposition (MOCVD) and observed ferromagnetism that was partially accounted to the spinodal decomposition and non-uniform distribution of Fe-rich magnetic nanocrystals. Kuwabara et al.7 reported the formation of nanoclusters and superparamagnetic behavior in GaN:Fe epilayers prepared by rf-plasma-assisted molecular beam epitaxy. In case of ion implantation the reports from different groups are quite controversial. Theodoropoulou et al.8 and Shon et al.9,10 did not relate ferromagnetic response to secondary phases after transition ion implantation into semiconductors. In our experiments, however, the formation of α-Fe nanoclusters, that were responsible for ferromagnetic response, was observed.11 Though the appearance of such precipitates is not desired in a DMS they might be useful for certain applications.12 Li et al.13 detected co-occurrence of α-Fe and ε-Fe<sub>3</sub>Nin MOCVD prepared GaN:Fe films and pointed out the role of nitrogen pressure and structural disorder in the formation of Fe-rich phases. Bonanni et al.14 have shown that the controlled aggregation of magnetic ions in a semiconductor can be affected by the growth rate and doping with shallow impurities.Recently we reported predominant formation of epitaxially oriented α-Fenanoclusters if Fe-doped samples were annealed in a N<sub>2</sub> flow at 1.1 bar pressure.11 In this paper we report the formation of ε-Fe<sub>3</sub>−<sub>x</sub>N with x<1 that builds up during annealing at 1073 K in 0.5 bar N2 and the reversible transformation to ε-Fe<sub>3</sub>Nduring cooling down to RT.P-type (Mg) doped (∼2×10<sup>17</sup>cm<sup>−3</sup>)single crystalline wurtzite GaN(001) films of about 3μm thickness epitaxially grown by metal organic vapor phase epitaxy on sapphire (001) were used. Samples, 7° tilted relative to the ion beam to avoid channeling, were implanted with 195 keV <sup>57</sup>Fe ions with fluence Φ=4×10<sup>16</sup>cm<sup>−2</sup> (peak Fe concentration of 4 at. 
LB  - PUB:(DE-HGF)16
UR  - <Go to ISI:>//WOS:000272627700057
DO  - DOI:10.1063/1.3271828
UR  - https://bib-pubdb1.desy.de/record/88666
ER  -