The role of Frenkel defect diffusion in dynamic annealing in ion-irradiated Si

Abstract

The formation of stable radiation damage in crystalline solids often proceeds via complex dynamic annealing processes, involving migration and interaction of ballistically-generated point defects. The dominant dynamic annealing processes, however, remain unknown even for crystalline Si. Here, we use a pulsed ion beam method to study defect dynamics in Si bombarded in the temperature range from −20 to 140 °C with 500 keV Ar ions. Results reveal a defect relaxation time constant of ~10–0.2 ms, which decreases monotonically with increasing temperature. The dynamic annealing rate shows an Arrhenius dependence with two well-defined activation energies of 73 ± 5 meV and 420 ± 10 meV, below and above 60 °C, respectively. Rate theory modeling, bench-marked against this data, suggests a crucial role of both vacancy and interstitial diffusion, with the dynamic annealing rate limited by the migration and interaction of vacancies.

Dynamic annealing in Ge studied by pulsed ion beams

“…3 alternate between the two simplest decay process equations: the first order ( n ( t off ) = n ∞ + ( n (0) − n ∞ ) exp (− t off / τ 1 )) and second order decay equations. This finding is in contrast to results of our recent pulsed beam study 19 of Si that has revealed a clear switch from the second to the first order decay at a certain T . However, both first and second order fits for Ge shown in Fig.…”

“…Comparing DA in Ge to that in other semiconductors, we note that our τ values of ~0.3–8 ms in Ge (at 100–160 °C) are similar to those for Si (~0.2–14 ms in a wider T range from −20 to 140 °C), 3 C -SiC ( τ = 3 ms at 100 °C), and 4 H -SiC ( τ of ~1–5 ms at 25–250 °C) recently measured with the pulsed ion beam technique 15 – 19 . Despite such similarity of the range of the τ values measured, the details of defect interaction dynamics are strongly material dependent.…”

“…An example of the first order decay process is the trapping of interstitials or vacancies at sinks, while vacancy–interstitial annihilation and the formation of di-vacancies are examples of the second order kinetic processes. Although it is tempting to associate the best fitting decay curves with some specific defect interaction processes, such assertions will require future modeling work as, for example, in a recent study of ion-bombarded Si 19 .…”

“…Similar to our previous work 15 – 19 , for τ measurements, the total ion fluence was split into a train of equal square pulses, each with an instantaneous dose rate ( F on ) of ~1.5×10 13 cm −2 s −1 and duration ( t on ) of 1 ms. Adjacent pulses in such τ measurements were separated by time t off , which was varied between 0.2 and 50 ms. For L d measurements 17 , 20 , 21 , the total fluence was delivered as a train of pulses with duration ( t on ) varying between 0.2 and 1 ms, each with an instantaneous dose rate ( F on ) of ~4.3×10 13 cm −2 s −1 , separated by a t off of 100 ms, which, as will be shown below, is much greater than the τ values.…”

“…1(a) shows a schematic of the time dependence of the instantaneous dose rate and defines the pulsing parameters ( t on , t off , and F on ). A more detailed description of the experimental arrangement can be found elsewhere 15 – 19 .

Figure 1 Selected depth profiles of relative disorder in Ge bombarded at 110 °C with a pulsed beam of 500 keV Ar ions with F on , t on , and t off given in the legends at total fluences of ( a ) 4.9 × 10 13 cm −2 and ( b ) 7.5 × 10 13 cm −2 .

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