Compositional dependence of damage buildup in Ar-ion bombarded AlGaN K. Pągowska 1 , R. Ratajczak 1 , A. Stonert 1 , L

1. Al2O3 GaN bulk ~ 40 nm ~ 1000 nm Compositional dependence of damage buildup in Ar-ion bombarded AlGaN K. Pągowska1, R. Ratajczak1, A. Stonert 1, L. Nowicki1 and A. Turos 1,2 1 Soltan Institute for Nuclear Studies, 05-400 Świerk/Otwock, Poland 2Institute of Electronic Materials Technology,Wólczyńska 133, 01-919 Warsaw, Poland AIM The detailed understanding of defect formation and transformations in AlGaN is of great interest for further material and device improvement. Because of the complexity of processes involved in defect buildup, many important issues are still to be elucidated. SAMPLE PREPARATION GaN, Al0.4Ga0.6N and AlN layers of 1 μm thickness were grown on sapphire substrates using the MOVPE technique. Epitaxial layers were bombarded with 320 keV Ar ions to fluence ranging from 5х1012 to 1х1017/cm2 at RT. EXPERIMENTAL RBS/channeling with 1.70 MeV4He-ions was used for analysis. The Monte Carlo simulationcode McChasy was applied for spectra evaluation. Fig. 1. Random and aligned RBS/channeling spectra for 1 μm thick GaN film bombarded to different fluences of 320 keV Arions. • RESULTS • Fig. 1 shows random and (0001) aligned spectra (Ga peak only) for 1 μm thick GaN epilayers subjected to Ar-ion bombardment to different fluences. Some characteristic features of spectra should be pointed out: • with increasing Ar fluence Ga damage peak increases monotonically due to the progressing damage builup in GaN layer, • for the highest fluence the implanted region was amorphized, • peak in the vicinity of the rear edge is due to the lattice mismatch between the layer and the substrate and is characteristic for heteroepitaxial GaN growth. • Similar spectra were obtained for Ar-ion implanted Al0.4Ga0.6N and AlN layers. Fig. 2. Depth distributions of displaced lattice atoms due to Ar-ion bombardment DISCUSSIONANDCONCLUSIONS Fig. 3 shows the defect buildup curves for studied alloys. The multistep damage accumulation model [1] has been fitted to the data. For comparison results of Ar-ion bombardment at 15 K [2] were also shown. At a given fluence phase transformations in bombarded epilayers occur, which are visualized as steps in calculated curves. Three step process has been assumed. Parameters of corresponding transitions are listed in Table 1. One notes that the critical fluence for the second step is independent of the Al molar quotient. Our preliminary HRXRD data indicate that the driving force for this effect is the strain accumulation in implanted layer. Besides of GaN the amorphization cannot be attained with 320 keV Ar-ion bombardment. Further increase of the ion fluence leads only to enhanced sputtering and cannot produce more damage. Table 1. MSDA model parameters: fdi- level of damage at saturation , σi-cross-section for damage formation (slope), xi- irradiation fluence in dpa, where i – stage number. REFERENCES [1] J. Jagielski et al. NIMB 266 (2008) 2902. [2] E.Wendler et al. NIMB 206 (2003) 1028. Fig. 3. Accumulated damage in GaN, AlGaN and AlN epilayers bombarded with 320 keV Ar ions. Solid lines are fits to RBS/C data using the MSDA model assuming a three-step process ACKNOWLEDGEMENTS This work was supported by the Polish Ministry of Science and Higher Education, Grant No. N 51502931/1104. RBS/channeling analysis has been carried out at the AIM of the Institute of Ion Beam Physics and Materials Research of the Forschungszentrum Dresden-Rossendorf within the framework of the specific research and technological development programme of the European Community "Structuring the European Research Area: Research Infrastructures Transnational Access” (RITA Contract Number 025646).