Epitaxial Crystallization

[Summary by Dr. T. Som (IOP,Bhubaneswar)]

Ion-beam-induced epitaxial crystallization (IBIEC) has been shown to take place in silicon and other materials at considerably lower target temperatures than necessary for thermal annealing when performed under irradiation [1,2]. IBIEC has unique characteristics such as low processing temperature, layer-by-layer and selective area crystallization, and dynamic defect annealing. In most of the existing reports, for low- to medium-energy IBIEC, recrystallization has been mainly ascribed to the migration and recombination of defects [at the amorphous/crystalline (a/c) interface] created by the nuclear energy loss (Sn). However, Nakata had pointed out about the possible role of inelastic-scattering processes in IBIEC [3]. Sahoo et al. [4] have shown swift heavy-ion (SHI)-induced recrystallization of Si where inelastic processes play a major role.   

 

In our recent works, we have shown electronic energy loss (Se) dominated IBIEC of an ion beam synthesized, buried Si3N4 layer at lower temperatures by using several ions. These include 100 MeV Ag, 70 MeV Si, and 100 MeV O ions. These ion species lead to very different energy loss values and have wide variant of masses as well. We observe recrystallization of the buried Si3N4 layer at 100°C for O ions, 150°C for Si ions, and 200°C for Ag ions at the fluence of 1×1014 ions cm-2 [5]. These data show an inverse linear relationship between the two and thus justify our argument that the recrystallization temperature decreases with an increasing Se /Sn ratio. SHI induced recrystallization in amorphous Si also shows a similar trend where the higher Se /Sn ratio causes a reduction in the activation energy and a higher regrowth rate for any given temperature. One such representative cross sectional transmission electron microscopy (XTEM) image is shown below which reveals the quality of the recrystallized layer and the nature of the interfaces.

 

In order to check the validity of the above prediction, we performed further experiments on a-Ge samples. However, it was found that exposure to 100 MeV Ag-ion irradiation to the fluence of 1×1014 ions cm-2 led to complete recrystallization of the a-Ge layer at room temperature [10]. On the other hand, 70 MeV Si and 100 MeV O ion irradiation did not lead to any recrystallization of the a-Ge layer. Thus, it may be inferred that SHIBIEC is a material dependent process and a lot needs to be done to have a clear understanding on the role of the Se/Sn ratio. More experiments are underway.

 

References

  1. J. S. Williams, R. G. Elliman, N. L. Brown, and T. E. Seidel, Phys. Rev. Lett. 55 (1985) 1482. 
  2. J. Linnros, B. Svensson, and G. Holmen, Phys. Rev. B 30 (1984) 3629; J. Linnros and G. Holmen, J. Appl. Phys. 59 (1986) 1513. 
  3. J. Nakata, Phys. Rev. B 43 (1991) 14643; J. Nakata, J. Appl. Phys. 79 (1996) 682. 
  4. P. K. Sahoo, T. Som, D. Kanjilal, and V. N. Kulkarni, Nucl. Instrum. Methods Phys. Res. B 240 (2005) 239; P.K. Sahoo, Ph.D. Thesis, IIT Kanpur (2004). 
  5. T. Som, B. Satpati, O. P. Sinha and D. Kanjilal, J. Appl. Phys. 98 (2005) 013532; T. Som, B. Satpati, O. P. Sinha, N. C. Mishra, and D. Kanjilal, Nucl. Instr. Meth. Phys. Res. B 244 (2006) 213; T. Som, B. Satpati, O. P. Sinha, D.K. Avasthi, D. Kanjilal, Nucl. Instr. Meth. Phys. Res. B 245 (2006) 255; T. Som, O. P. Sinha, J. Ghatak, B. Satpati and D. Kanjilal, J. Appl. Phys. 101 (2007) 034912; T. Som, O. P. Sinha, J. Ghatak, B. Satpati and D. Kanjilal, Defense Sci. J. 59 (2009) 351. 
  6. T. Som, J. Ghatak, O. P. Sinha, R. Sivakumar and D. Kanjilal, J. Appl. Phys. 103 (2008) 123532.
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