Quantitative Correlation Study of Dislocation Generation, Strain Relief, and Sn Outdiffusion in Thermally Annealed GeSn Epilayers

Abstract

The instability during the growth and processing of epitaxial GeSn layers with high Sn molar fraction and high compressive strain is still to be fully studied. In this work, the relationship among strain relief, dislocations, and Sn outdiffusion in GeSn layers with a Sn content of ∼9 atom % was studied as a function of pre-existing misfit/threading dislocation (MD/TD) density and annealing time at 300 °C. For a GeSn epilayer strained to a Ge-on-Si virtual substrate (Ge-VS), an increase of strain relief by a factor of ∼2 is observed after 2 h of annealing, without a significant effect on strain relaxation for a more prolonged temperature treatment. This is explained by the limited propagation or elongation of pre-existing MDs at the interface of GeSn/Ge-VS. The onset of Sn outdiffusion and the appearance of segregation spots are observed for the GeSn epilayers with significant strain relaxation (≥50%) before annealing, for which the density of MDs ≥ 2 × 10 5 cm −1 . This is explained by generation of high-density MDs/TDs acting as preferential sites for Sn accumulation during the growth of the GeSn layer. This work explicitly provides an understanding that dislocation engineering is one of the key factors for the stability and performance of GeSn semiconductors.

Atomic Pathways of Solute Segregation in the Vicinity of Nanoscale Defects

“…The difference between this critical temperature and the growth temperature vanishes progressively as the layer's Sn content increases. In partially relaxed layers with pre-existing dislocations, the scenario is quite different, with the layers initially showing further plastic relaxation and the onset of Sn diffusion taking place at much lower temperatures, 26 as it was observed in the highly dislocated regions of the current samples. The Sn atoms in GeSn have a strong tendency to reach the surface from the bulk layers.…”

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

“…The other three samples were subjected to thermal treatments at 300 • C in vacuum for 2, 4, and 8 h, respectively. X-ray diffraction (Panalytical X'pert Pro MRD diffractometer) (Panalytical, Amsterdam, Netherlands)measurements (Figure 1), including reciprocal space maps (RSMs) (Figure 2), coupled with modeling [18], were used to determine the lattice constants, Sn compositions, strain parameters, and misfit dislocations, of the annealed and unannealed samples.…”

“…The simulation of RSM was performed according with the kinematic theory of X-ray diffraction as described in Ref. [18]. Additionally, the structural quality of all samples is compared by measuring the full width at half-maximum (FWHM) of the GeSn (004) rocking curves (see Figure S3 and Table S1 in the Supplementary Material section).…”

“…In fact, the role of strain is made very clear in a comprehensive study of optical transitions in Ge 0.875 Sn 0.125 via PL measurements as a function of temperature, compressive strain and excitation power [17]. Complementing these studies, Stanchu et al [18] recently demonstrated a correlation between strain relief, misfit dislocations, and Sn out-diffusion in thermally annealed GeSn at 300 • C. Together, these studies point out the possible existence of a strong connection between (1) strain, (2) composition, (3) defect density and (4) the performance of GeSn optical devices operating at temperatures, at and above, room temperature.…”

“…Interestingly, the optical properties of GeSn samples, with a composition near the transition point, are very sensitive to changes in composition or strain. On the experimentally side, despite the low-equilibrium solid solubility of Sn in Ge of only 1% [11], growth under compressive strain of high Sn concentrations has been achieved, demonstrating the indirect-to-direct transition [12][13][14] and fabrication of direct bandgap GeSn devices with high optical emission efficiency [15][16][17][18]. However, how much Sn can be achieved in GeSn and how stable GeSn with high Sn content can be at operating temperatures above room temperature, must be investigated.…”