Impact of Long-Term Annealing on Photoluminescence from Ge1−xSnx Alloys

Abstract

We report on the connection between strain, composition, defect density and the photoluminescence observed before and after annealing at 300 °C for GeSn samples with Sn content of 8% to 10%. Results show how the composition and level of strain influenced the separation between the indirect and direct optical transitions, while changes in the level of strain also influenced the density of misfit dislocations and surface roughness. The effect of annealing is observed to lower the level of strain, decreasing the energy separation between the indirect and direct optical transitions, while also simultaneously increasing the density of misfit/threading dislocations and surface roughness. The reduction in energy separation leads to an increase of photoluminescence (PL) emission, while the increase of misfit/threading dislocations density and surface roughness results in a decrease of PL. Consequently, the competition between these factors is observed to determine the impact of annealing on the PL. As a result, annealing increases the collected PL for small (≤40 meV) separation between the indirect to direct optical transitions in the as-grown sample while decreases the PL for larger (≥60 meV) separations. More generally, these numbers have a small dependence on the level of strain in the as-grown samples.

3D Nanoscale Mapping of Short‐Range Order in GeSn Alloys

“…The 3D SRO mapping shows a relatively large fluctuation of Sn-Sn 1NN SRO parameter Sn Sn KNN α − from 0.85 to 1.15. This Sn-Sn 1NN SRO fluctuation in GeSn, together with the theoretical prediction of large band structure variation with SRO, [3] contributes to the bandedge softening compared to pure Ge, as commonly observed in GeSn absorption spectra as well as PL peak width >> k B T thermal broadening even at 10 K. [34][35][36][37] The SRO mapping also indicates more preference toward Sn-Sn clustering near the surface, consistent with the tendency of Sn surface segregation. Furthermore, the SRO mapping shows that compressive strain tends to favor Sn-Sn 1NN, indicating that strain relaxation or tensile strain helps to prevent undesirable Sn-Sn clustering or segregation.…”

“…Our study shows that fluctuates between 0.85 and 1.15 in different regions. This Sn–Sn 1NN SRO fluctuation in GeSn, together with the theoretical prediction of large band structure variation with SRO, contributes to the band edge softening compared to pure Ge, as commonly observed in GeSn absorption spectra as well as photoluminescence (PL) peak width >> k B T thermal broadening even at 10 K. [ 34–37 ] The mean value of decreases from 1.052 ± 0.051 to 1.026 ± 0.045 as the depth increase from 150 to 800 nm under the surface, with eighteen, 10 nm × 10 nm × 10 nm nanocubes examined at each depth. These results indicate more preference toward Sn–Sn clustering near the surface, consistent with the tendency of Sn surface segregation.…”

Auger-limited minority carrier lifetime in GeSn/SiGeSn quantum well

“…Photoluminescence is often used as a qualitative measure of material quality, but its strong dependencies on excitation conditions, optical throughput, and sample geometry largely prevents any widescale comparison of steady-state photoluminescence (SSPL) results between research groups. [6][7][8][9][10] The fundamental driver of photoluminescence output and thus a more quantifiable metric for optoelectronic quality is the minority carrier recombination lifetime of the photogenerated electron-hole pairs, a material property that can be most easily extracted from measurement of the time-resolved photoluminescence (TRPL) decay.…”