Tracks and Voids in Amorphous Ge Induced by Swift Heavy-Ion Irradiation

Ion tracks formed in amorphous Ge by swift heavy-ion irradiation have been identified with experiment and modeling to yield unambiguous evidence of tracks in an amorphous semiconductor. Their underdense core and overdense shell result from quenched-in radially outward material flow. Following a solid-to-liquid phase transformation, the volume contraction necessary to accommodate the high-density molten phase produces voids, potentially the precursors to porosity, along the ion direction. Their bow-tie shape, reproduced by simulation, results from radially inward resolidification.

Figure 1

(a) Background-subtracted SAXS intensity as a function of scattering vector for ion tracks including the detector image recorded with the surface normal at 10° to the x-ray direction (bottom left) and the calculated radial density distribution (top right). (b) Background-subtracted SAXS intensity as a function of scattering vector for voids including the detector image recorded with the surface normal at 5° to the x-ray direction (bottom left). The void geometry used for fitting (top right) was 10.6, 7.4, and 6.6 nm for $L$, $R_1$, and $R_2$, respectively.

Figure 2

XTEM image from $a$-Ge irradiated to a fluence of $6\times {10}^{10}/{\mathrm{cm}}^2$ (left) and MD simulation of the void geometry following resolidification (300 ps) (right).

Figure 3

MD simulation of the time-dependent radial density distribution across an (a) ion track and (b) void. In (a), the reduction in density at $\sim 10\mathrm{nm}$ radial distance for times 100-130 ps is an artifact from changing the potential at 100 ps.