Synthesis of Ge1−x Sn x Alloy Thin Films Using Ion Implantation and Pulsed Laser Melting (II-PLM)

Suppression of ion-implantation induced porosity in germanium by a silicon dioxide capping layer

“…Indeed, the measured step height is reduced to $ À 24 nm below the original Ge surface. On the other hand, on the samples with the capping layer, no volumetric expansion can be detected: the step height shows an almost linear reduction with fluence of $3:1 nm=1 Â10 16 ion cm À2 , consistent with sputter erosion of the cap. Essentially, the thin capping layer appears to be very effective at suppressing Ge pore formation.…”

“…However, Ge readily becomes porous after a moderate fluence implant ($1 Â 10 15 ion cm À2 ) at room temperature, and for heavy ion species such as tin (Sn), holding the target at liquid nitrogen (LN 2 ) temperature suppresses porosity formation only up to a fluence of 2 Â 10 16 ion cm À2 . We show, using stylus profilometry and electron microscopy, that a nanometer scale capping layer of silicon dioxide significantly suppresses the development of the porous structure in Ge during a Sn À implant at a fluence of 4:5 Â 10 16 ion cm À2 at LN 2 temperature. The significant loss of the implanted species through sputtering is also suppressed.…”

“…Recently, there have been several efforts to fabricate the material with a more robust, industrially relevant method using ion implantation in combination with nanosecond pulsed laser melting (PLM). [16][17][18] For example, a good quality Ge-Sn alloy with a Sn concentration greater than 6 at:% has been recently obtained using PLM, 18 demonstrating the potential of this approach. It was shown, however, that achieving Sn concentrations in Ge higher than about 6 at:% through ion implantation is severely hindered by a high sputtering effect in Ge and the onset of ionimplantation induced porosity once the Ge is rendered amorphous (a-Ge).…”

“…The implantation of Sn was conducted with a low energy implanter at energies of 100 À 120 keV at LN 2 temperature and fluences up to 5 Â 10 16 ion cm À2 with an ion flux of 1:4 Â 10 13 ion cm À2 s À1 . According to the Stopping and Range of Ions in Matter simulation (SRIM), the projected range of the Sn ions in Ge is 34:6 nm and the peak concentration of Sn is $14% for an implant of 3 Â 10 16 ion cm À2 at 100 keV, where the density of bulk Ge of 4:41 Â 10 22 atom cm À3 was used to calculate the Sn concentration. Physical characterisation of the as-implanted samples was carried out using a stylus profilometer, Rutherford backscattering spectrometry (RBS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM).…”

Synthesis of Ge1−xSnx alloys by ion implantation and pulsed laser melting: Towards a group IV direct bandgap material

“…Nevertheless, research on Ge 1Àx Sn x by ion-beam synthesis has been so far only marginally successful. Although the first report on this subject 23 presented the incorporation of 2 at: %Sn in Ge, the material quality was poor, having an obvious porous structure on the surface as well as a low degree of crystallisation. An a)…”