Compositional dependence of damage buildup in Arion bombarded

Compositional dependence of damage buildup in Ar-ion bombarded Al. Ga. N K. 1 Pągowska , R. 1 Ratajczak , A. 1 Stonert , L. 1 Nowicki and A. Turos 1, 2 Soltan Institute for Nuclear Studies, 05 -400 Świerk/Otwock, Poland 2 Institute of Electronic Materials Technology, Wólczyńska 133, 01 -919 Warsaw, Poland 1 AIM The detailed understanding of defect formation and transformations in Al. Ga. N 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. bulk Nucleation Layer Al 2 O 3 ~ 40 nm Ga. N ~ 1000 nm SAMPLE PREPARATION Ga. N, Al 0. 4 Ga 0. 6 N and Al. N layers of 1 μm thickness were grown on sapphire substrates using the MOVPE technique. Epitaxial layers were bombarded with 320 ke. V Ar ions to fluence ranging from 5 х1012 to 1 х1017/cm 2 at RT. EXPERIMENTAL RBS/channeling with 1. 70 Me. V 4 He-ions was used for analysis. The Monte Carlo simulation code Mc. Chasy was applied for spectra evaluation. Fig. 1. Random and aligned RBS/channeling spectra for 1 μm thick Ga. N film bombarded to different fluences of 320 ke. V Ar ions. RESULTS Fig. 1 shows random and (0001) aligned spectra (Ga peak only) for 1 μm thick Ga. N 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 Ga. N 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 Ga. N growth. Similar spectra were obtained for Ar-ion implanted Al 0. 4 Ga 0. 6 N and Al. N layers. Fig. 2. Depth distributions of displaced lattice atoms due to Ar-ion bombardment DISCUSSION AND CONCLUSIONS 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 Ga. N the amorphization cannot be attained with 320 ke. V Ar-ion bombardment. Further increase of the ion fluence leads only to enhanced sputtering and cannot produce more damage. Table 1. MSDA model parameters: Ga. N Wendler fdi- level of damage at saturation , σi-cross-section for damage formation (slope), xi- irradiation fluence in dpa, where i – stage number. Al 0. 4 Ga 0. 6 N Al. N fd 1 6 7. 5 6 0. 5 σ1 0. 77 2. 15 4. 8 0. 5 fd 2 70 75 42 6. 5 σ2 0. 151 0. 258 0. 16 7. 8 x 2 3 2. 1 0. 7 0. 06 fd 3 100 54 63. 5 σ3 0. 02 0. 079 0. 022 0. 168 x 3 88 14 60 1. 26 REFERENCES [1] J. Jagielski et al. NIMB 266 (2008) 2902. [2] E. Wendler et al. NIMB 206 (2003) 1028. Fig. 3. Accumulated damage in Ga. N, Al. Ga. N and Al. N epilayers bombarded with 320 ke. V 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).